forest disturbance: breeding ecology … publications/thesis...forest disturbance: breeding ecology...

FOREST DISTURBANCE: BREEDING ECOLOGY RESPONSE OF SONGBIRDS

by

JILL M. WICK

A THESIS

Submitted in partial fulfillment of the requirements for the degree of Master of Science

in the Department of Natural Resources and Environmental Science in the School of Graduate Studies

Alabama A&M University Normal, AL 35762

May 2008

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Submitted by JILL M WICK in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE specializing in WILDLIFE SCIENCE.

Accepted on behalf of the Faculty of the Graduate School by the Thesis Committee:

____________________________ Major advisor ____________________________ ____________________________ ____________________________

____________________________ Dean of the Graduate School ____________________________ Date

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Copyright by

JILL M. WICK

2008

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This thesis is dedicated to my biggest supporters: my parents, Norm and Diane

Wick; and my siblings, Joel, Jason, and Molly Wick.

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FOREST DISTURBANCE: BREEDING ECOLOGY RESPONSE OF SONGBIRDS

Jill Wick, B.S. University of Wisconsin at Stevens Point, 2002

Thesis Advisor: Yong Wang

Many migratory songbird species have experienced declines over the past four decades,

possibly due to loss of habitat. Forest management practices have the potential to create

suitable avian habitat. My research examined the effect of tree thinning and prescribed

burning on the breeding songbird community structure and avian individual fitness

(breeding success measured by home range size and nesting success) with a replicated

field experiment instead of focusing only on species abundance and richness, as much

past research has. The research was part of a comprehensive ecosystem research project

through collaboration with other researchers at Alabama A&M University and the USDA

Forest Service. I collected field data for one year pre treatment and one year post

treatment on the bird community composition and structure, microhabitat characteristics,

and microclimate conditions. One year after treatment, I collected data on arthropod

availability (avian food source) and home range and habitat selection of two songbird

species, the hooded warbler (Wilsonia citrina Boeddart) and the worm-eating warbler

(Hemithoeros vermivora Gmelin). Thinning had a greater impact on the bird community

than burning, although burning affected the bird community on a smaller scale. There

was an increase of shrub nesting and foliage foraging species on thinned plots, as well as

an increase in interior/edge species that use early successional habitats. However, the

thinning treatment did not displace most of the interior forest birds. The low intensity

prescribed burns had less of an effect on the bird community, however diversity increased

following treatment. Thinning and burning in combination resulted in decreased

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diversity, a decrease in tree and cavity nesting and foliage foraging species. Interior/edge

species decreased and open/edge species increased. It appears that thinning and burning

in combination has more negative effects on the bird community than either treatment

alone. Hooded warbler home ranges ranged from 3.41 ha to 13.05 ha; worm-eating

warbler home ranges ranged from 4.38 ha to 8.81 ha. Core areas ranged from 2.19 ha to

5.84 ha for hooded warblers and 1.88 ha to 3.01 ha for worm-eating warblers. Hooded

warblers selected habitat with high herbaceous ground cover and vertical cover. Worm-

eating warblers selected habitat with an increased presence of slopes and high vertical

cover. It appears that understory forest structure is a key habitat feature for both species.

Keywords: Avian community, bird community, Cumberland Plateau, habitat selection,

hooded warbler, home range, prescribed burning, silviculture, thinning, worm-eating

warbler.

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TABLE OF CONTENTS

CERTIFICATE OF APPROVAL………………………………………………….. ii

ABSTRACT AND KEYWORDS…………………………………………………. v

LIST OF TABLES…………………………………………………………………. vii

LIST OF FIGURES.……………………………………………………………….. x

ACKNOWLEDGEMENTS……………………………………………………….. xvi

CHAPTER 1: INTRODUCTION, OBJECTIVES, HYPOTHESES, AND LITERATURE

REVIEW

Introduction……………………………………………………………………. 1

Hypotheses……………………………………………………………………... 2

Literature Review……………………………………………………………….4

Forest management…………………………………………………..…….. 4

Home range size………………………………………………………......... 8

Importance of the Study………………………………………………….…….. 11

Bibliography…………………………………………………………………… 12

CHAPTER 2: MICROCLIMATE, MICROHABITAT, AND BIRD COMMUNITY

CONDITIONS BEFORE STAND TREATMENT

Introduction…………………………………………………………………….. 16

Study Area and Methods……………………………………………………….. 17

Study Area…………………………………………………………………. 17

Sampling…………………………………………………………………… 19

Microclimate……………………………………………………….. 19

Microhabitat………………………………………………………... 19

Bird sampling………………………………………………………. 20

Data Analysis………………………………………………………………. 20

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Results………………………………………………………………………….. 24

Microclimate……………………………………………………….. 24

Microhabitat………………………………………………………... 26

Bird Community…………………………………………………… 26

Canonical correspondence analysis………………………………... 33

Discussion……………………………………………………………………… 36

Bibliography…………………………………………………………………… 39

CHAPTER 3: MICROCLIMATE, MICROHABITAT, ARTHROPOD AVAILABILITY,

AND BIRD COMMUNITY IN STANDS TREATED WITH THINNING AND

BURNING.

Introduction…………………………………………………………………….. 42

Study Area and Methods……………………………………………………….. 43

Study Area…………………………………………………………………. 43

Sampling…………………………………………………………………… 47

Microclimate………………………………………………………. 47

Microhabitat………………………………………………………... 47

Arthropod Abundance……………………………………………… 48

Bird sampling………………………………………………………. 49

Data Analysis………………………………………………………………. 49

Results………………………………………………………………………….. 54

Microclimate……………………………………………………….. 54

Microhabitat………………………………………………………... 62

Arthropod availability……………………………………………… 67

Bird Community…………………………………………………… 70

Canonical correspondence analysis………………………………... 79

Discussion……………………………………………………………………… 83

Bibliography…………………………………………………………………… 87

CHAPTER 4: HOME RANGE SIZE, HABITAT USE, AND REPRODUCTIVE

SUCCESS OF HOODED WARBLERS AND WORM-EATING WARBLERS IN

THINNED FOREST STANDS

Introduction……………………………………………………………………. 92

Study Area and Methods………………………………………………….... 93

Study Area………………………………………………………………..... 93

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Target Species…………………………………………………………….... 96

Sampling…………………………………………………………………… 96

Radiotelemetry……………………………………………………... 96

Reproductive success…………………………………………......... 97

Microhabitat………………………………………………………... 97

Data Analysis…………………………………………………………......... 98

Home range delineation………………………………………......... 98

Reproductive success…………………………………………......... 99

Microhabitat………………………………………………………... 100

Results………………………………………………………………………….. 100

Home range………………………………………………………… 100

Microhabitat ………………………………………………………. 102

Reproductive success……………………………………………… 106

Discussion……………………………………………………………………… 108

Bibliography…………………………………………………………………… 113

CHAPTER 5: DISCUSSION AND CONCLUSION

Conclusion……………………………………………………………………... 117

Management recommendations………………………………………………... 119

Bibliography…………………………………………………………………… 120

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LIST OF TABLES

Table 2.1 Guild memberships of detected bird species………………………… 22

Table 2.2. Microclimate characteristics………………………………………… 25

Table 2.3. Principle component analysis loadings for microclimate variables….. 27

Table 2.4. Microhabitat characteristics…………………………………………. 28

Table 2.5. Principle component analysis loadings for microhabitat variables…...29

Table 2.6. Significance values and means for pre-treatment bird community

characteristics……............................................................................... 30

Table 2.7. Species of continental importance detected on plots………………… 31

Table 2.8. Morisita’s similarity index for bird community…………………....... 32

Table 3.1. Guild memberships of detected bird species…………………………51

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Table 3.2. Results of two-way analysis of variance for microclimate……………... 55

Table 3.3. Results of two-way analysis of variance for changes in

microclimate………………………………………………………… 57

Table 3.4. Results of one-way analysis of variance for microclimate…………... 59

Table 3.5. Results of one-way analysis of variance for changes

in microclimate…………………………………….………………… 60

Table 3.6. Principle component loadings for microclimate variables………...... 61

Table 3.7. Results of one-way analysis of variance for microhabitat variables… 65

Table 3.8. Results of one-way analysis of variance for changes in

microhabitats………………………………………………………… 66

Table 3.9. Principle component loadings for microhabitat variables…………… 68

Table 3.10. Results of one-way analysis of variance for arthropod index………... 69

Table 3.11. Results of one-way analysis of variance for bird community……….. 74

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Table 3.12. Results of one-way analysis of variance for

changes in bird community………………………………………….. 76

Table 3.13. Species of continental importance detected on plots………………… 77

Table 3.14. Morisitia’s similarity index for bird community one

year after treatment………………………………………………….. 78

Table 3.15. Morisitia’s similarity index for bird community before treatment

and one year after treatment…………………………………………. 78

Table 4.1. Distribution of radio tracked birds among treatments……………….. 101

Table 4.2. Significance values and means of core area

size and home range size…………………………………………….. 103

Table 4.3. Principle component loadings for habitat variables…………………. 105

Table. 4.4. AIC scores for logistic regression models…………………………… 107

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LIST OF FIGURES

Fig. 1.1. Effect of forest disturbance on avian fitness through alteration of available

resources…………………………………………………………….. 2

Fig 2.1. Location of study sites in Bankhead National Forest, Alabama…...... 18

Fig. 2.2. Canonical correspondence analysis of bird species abundance and

microhabitat variables…………………….......................................... 34

Fig. 2.3. Canonical correspondence analysis of nesting guild abundance and

microhabitat variables…………………………………....................... 35

Fig. 2.4. Canonical correspondence analysis of foraging guild abundance and

microhabitat variables……………………………………………….. 37

Fig. 3.1. Location of study sites in Bankhead National Forest, Alabama…….. 45

Fig. 3.2. Experimental design…………………………………………………. 45

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Fig. 3.4. Interaction between burning and thinning in litter depth……………. 63

Fig. 3.5. Interaction between burning and thinning in the change

in forest level 3………………………………………………………. 64

Fig. 3.6. Interaction between burning and thinning in the

change in diversity index……………………………………………. 64

Fig. 3.7. Interaction between burning and thinning in the change in cavity nesting

abundance……………………………………………………………. 71

Fig. 3.8. Interaction between burning and thinning in the change in foliage foraging

abundance……………………………………………………………. 71

Fig. 3.9. Interaction between burning and thinning in the change in resident species

abundance……………………………………………………………. 72

Fig. 3.11. Canonical correspondence analysis of bird species abundance and

microhabitat variables……………………………………………...... 73

Fig. 3.12. Canonical correspondence analysis of nesting guild abundance and

microhabitat variables………………………………………………... 81

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Fig. 3.13. Canonical correspondence analysis of foraging guild abundance and

microhabitat variables. ……………………………………………… 82

Fig. 4.1. Location of study sites in Bankhead National Forest, Alabama……... 94

Fig. 4.2. Experimental design…………………………………………………. 94

Fig. 4.3. Example home range distribution for a hooded warbler and worm-eating

warbler……………………………………………………………….. 104

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ACKNOWLEDGEMENTS

I thank my advisor, Yong Wang, and my committee members, Callie Schweitzer,

William Stone, and Ken Ward for their guidance and advice throughout my course of

study. Zach Felix and Bill Sutton provided invaluable support and advice throughout my

research and for that I thank them. I also thank fellow graduate students, field

technicians, and others who have provided their help in the field and in the office:

Carleen Bailey, Matthew Bolus, Rachel Bru Bolus, John Carpenter, Drew Fowler,

Heather Howell, Lisa Gardner-Barillas, Daryl Lawson, Dawn Lemke, Kimi Sangalang,

Ryan Sisk, Molly Wick, Kelvin Young, and Joel Zak.

This publication “SONGBIRD BREEDING ECOLOGY: RESPONSE TO

FOREST MANAGEMENT” was developed under GRO Research Assistance Agreement

No. MA916706 awarded by the U.S. Environmental Protection Agency. It has not been

formally reviewed by the EPA. The views expressed in this document are solely those of

Jill Wick and the EPA does not endorse any products or commercial services mentioned

in this publication.

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CHAPTER 1

INTRODUCTION, OBJECTIVES, HYPOTHESES, AND LITERATURE REVIEW

Introduction

Many migratory bird species have experienced population declines in the past

four decades, primarily due to loss of suitable habitat from anthropogenic environmental

disturbances (Askins et. al. 1990, Donovan and Flather 2002, Rappole and McDonald

1994). One of the factors contributing to the loss of suitable habitat for many bird

species in the United States is the prevention of disturbances, such as fire, wind throw,

beaver activity, floods, and forest management, which create and sustain early

successional forests (Askins 2001, Trani et al. 2001).

Canopy reduction and prescribed burning have been used to simulate natural

disturbance. Early research shows that such disturbance can affect the abundance and

availability of the resources on which birds rely (Weins 1989) (Fig. 1.1). Disturbance

can trigger changes in microclimate, habitat structure, food and nest-site availability,

predation, and nest-parasitism (Wiens 1989). Such alterations in turn affect the

likelihood of breeding success and fitness (an individual's contribution to the breeding

population in the next generation) of birds.

I studied the effect of forest disturbances, specifically thinning and prescribed

burning, on the avian community. I examined the effects of these disturbances on avian

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species richness and abundance. In addition, I examined the mechanisms (microclimate,

habitat structure and composition, food availability, and brood parasitism) responsible for

changes in avian population demographics. My objectives were to (1) examine

differences in microclimate and microhabitat among disturbance levels, (2) determine

relationships between microhabitat and avian community structure, (3) determine the

effect of forest disturbance on food availability, (4) determine relationships between

forest disturbance and avian territory size, and (5) determine the relationship between

forest disturbance and avian breeding success.

Research Predictions

Microhabitat and microclimate parameters will be affected by changes in

canopy density. Hypothesis 1: (1) Vegetation structure will be more complex in stands

thinned than those burned. (2) Vegetation composition will be more complex in stands

burned than those thinned. (3) Temperature will be indirectly related to the amount of

canopy reduction, whereas moisture will have a direct relationship with canopy

reduction.

Resource Abundance

Resource Availability

Resource Use

Resource Allocation

Individual Performance

“Fitness”

Population Patterns

Community Patterns

Forest environmental disturbance

Foraging Territory Nest site

Productivity Survivalship

Figure 1.1. Effect of forest disturbance on avian fitness

through alteration of available resources. Modified based

on Wiens (1989).

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Avian species richness and relative abundance will vary throughout

treatment types and will be correlated with habitat heterogeneity. Hypothesis 2: (1)

Avian species richness and abundance will be greatest in thinned stands due to increased

understory habitat heterogeneity and complexity (Wiens 1989). (2) Abundance of

canopy nesting and foraging birds will be lower on thinned stands due to decreased

overstory habitat complexity. (3) Abundance of sub-canopy nesting and foraging birds

will be higher on treated stands due to increased understory habitat complexity. (4)

Abundance of ground nesting and foraging birds will be lower on burned stands due to

decreased litter layer.

Food availability will be affected by changes in forest structure. Hypothesis

3: (1) Foliage feeding insect abundance will be directly related to increased leaf growth.

Avian home range size will vary among the treatments and will be correlated

with food availability, and size of individuals. Hypothesis 4: (1) Home range size for

ground nesting birds will be directly related to canopy reduction, due to decreased food

resources with high disturbance (thin*burn). (2) Sub-canopy nesting birds will have

larger home ranges on treated increased due to decreased habitat complexity. (3) Larger

individuals will have larger territories than smaller birds (Fretwell and Lucas 1970).

Nest success will vary among the treatments and will be correlated with food

availability, presence of predators, and presence of brood parasites. Hypothesis 5:

(1) Increased brood parasitism will be seen in thinned stands due to a more open canopy

(Chambers et al. 1999, Evans and Gates 1997). (2) Ground nesting birds will have lower

nesting success in burned stands due to the reduction of nesting substrate and food

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availability. (3) Sub-canopy nesting birds will have lower nesting success on treated

stands due to decreased habitat complexity and food resources.

Literature Review

Forest management

Forest managers have the ability to employ a variety of silvicultural techniques,

depending on their management goal. Intermediate stand treatments are used to enhance

stand composition, structure, growth, health and quality by regulating and controlling tree

growth through adjusting tree density or species composition (Smith et al. 1997). These

treatments do not direct any effort at regeneration. Thinning treatments impact stand

growth, development and structure; and enhances vigorous tree growth of selected trees

through the removal of the competitors (Smith et al. 1997). If sunlight is the main

limiting factor for the desired trees, thinning from above is used to reduce competition for

sunlight (Smith et al. 1997). If water is the main limiting factor for the desired trees,

thinning from below is used to reduce the competition for water in the soil (Smith et al.

1997). Free thinning removes trees to control stand spacing (density) and favor desired

trees without strict regard to crown position (Smith et al.1997).

Prescribed fires that are slow and low-burning are used as a silvicultural tool in

many western systems and in savannah habitats however; in eastern forests; the use of

prescribed fire is less common. In the eastern United States, fire has historically been

used to keep forest open for hunting (by Native Americans) and to clear land for pastures

and grazing (by early farmers). Forest managers use fire to reduce or eliminate fuel loads

and undesirable vegetation, to prepare seedbeds for regeneration of wind-disseminated

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species, to control competing vegetation, and control pests (Smith et al. 1997). Fire also

stimulates herbaceous species and sprouts of woody plants, so it is used to create or

improve wildlife habitat (Smith et al. 1997).

The response of birds to forest management varies by the degree of disturbance

and type of disturbance. Density and productivity of birds that use mature hardwood

forests tend to decline with tree removal, whereas early successional species tend to

experience an increase in density and productivity (Gram et al. 2003). More intensive

cutting results in more dramatic changes in abundance, species richness, and density.

Clearcuts cause species composition to change drastically (Brawn et al. 2001, Chambers

et al. 1999, Harrison and Kilgo 2004), and cause decreased density (Harrison and Kilgo

2004), species richness, (Harrison and Kilgo 2004) and abundance (Chambers et al.

1999). Some birds will use clearcuts for foraging, but do not nest in these areas

(Chambers et al. 1999). Gram et al. (2003) found higher densities of early successional

species after clearcuts, but densities of mature forest species declined. Productivity of

mature forest birds also declined in clearcuts, whereas productivity increased for some

early successional species.

Thinning has the potential to create conditions similar to those caused by natural

disturbance. Thins that retain a greater number of trees will mimic small-scale

disturbance, whereas thins that retain a few trees will mimic large-scale disturbance

(Harrison et al. 2005). In bottomland hardwood habitat, lower levels of tree retention (0

-20%) result in lower species richness and a lower similarity value between pre- and post-

treatment bird communities (Harrison et al. 2005). Birds that are more dependent on

trees and shrubs for nesting or foraging benefit from more residual trees, whereas ground

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dwellers are less affected by how many trees are retained (Tittler et al. 2001). Over time,

ground nesting and foraging birds increase, but these increases are by open-habitat or

generalist species, and not forest dwelling birds, as were present before thinning

(Harrison et al. 2005, Tittler et al. 2001). Lang et al. (2002) found that thinning and

burning to create red-cockaded woodpecker (Picoides borealis Vieillot) habitat did not

affect the daily movements of adult wood thrushes (Hylociclha mustelina Gmelin),

however fledglings on treated areas moved farther from their nest than those on untreated

areas. The habitat preferences of adults altered slightly after treatment; they preferred to

use riparian areas more than upland areas (Lang et al. 2002).

Group selection cuts are often used to mimic small-scale natural forest

disturbances by creating small gaps in the forest (Jobes et al. 2004). Group selection cuts

increase understory plant production, providing more opportunity for lepidopteron larvae

and creating habitat used by many early successional species (Blake and Hoppes 1986).

Studies report decreased abundance and diversity in group selection cuts compared to

control sites in western coastal forests (Chambers et al. 1999), however in eastern

hardwood forests, densities of early successional species increased (Gram et al. 2003). In

southeastern bottomland forests, worm-eating warbler (Helmitheros vermivorus Gmelin)

densities declined in both group selection cuts and clearcuts, however they rebounded

more quickly in group selection cuts (Harrison and Kilgo 2004). Hooded warblers

(Wilsonia citrina Boddaert) and indigo buntings (Passerina cyanea Linnaeu) had higher

nesting success in group selection cuts than in clearcut hardwood stands (Alterman et al.

2005, Whittam et al. 2002).

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Prescribed burning is used in many different ecosystems and has different effects

in each. In oak savannas, avian density and species richness were lower in unburned than

in frequently burned sites (Davis et al. 2000), whereas density and species richness in

coastal sage scrub and Florida pine scrub were higher in unburned sites (Greenberg et al.

1995, Stanton 1986). Other studies have found no changes in species richness when

comparing burned areas to unburned areas (Artman et al. 2001, White et al. 1999). White

et al. (1999) found burned pine forests to be preferred nesting habitat over unburned sites

for a variety of species; however, productivity rates in these sites were low. In mixed-

oak forests in Ohio, densities of ground and low-shrub nesting birds declined in burned

sites compared to unburned sites (Artman et al. 2001, Blake 2005). In burned sites,

hooded warblers shifted their territories and wood thrushes moved their nests from xeric

and intermediate sites to mesic sites (Artman and Downhower 2003, Artman et al. 2001).

Wood thrushes also placed their nests higher off the ground and in areas where burn

intensity was low. Due to this, nest survival rates did not differ between sites (Artman

and Downhower 2003). Apparently, the birds were able to minimize the affects of

burning by altering their nest placement.

The effect of forest management on nest parasitism rates is inconclusive. Some

studies report that the effects of fragmentation on nest parasitism rates in forested

ecosystems are negligible (Alterman et al. 2005, Artman and Downhower 2003, Harrison

and Kilgo 2004, Stuart-Smith and Hayes 2003), whereas other studies found parasitism

rates to be related to forest edges (Evans and Gates 1997, Moorman et al. 2002). Evans

and Gates (1997) found the highest occurrence of cowbirds at forest-brush and forest-

stream edges, with the probability of parasitism greater nearer to the edge. Cowbird

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occurrence is higher in open-canopy plots than closed-canopy plots (Evans and Gates

1997, Chambers et al. 1999). Areas with high basal area of snags and high total

vegetation volume are also correlated with high cowbird use because they provide

perches from which cowbirds can search for host nests (Evans and Gates 1997).

Nest predation is the major cause of nest failure for passerines (Alterman et al.

2005, Artman and Downhower 2003, Harrison and Kilgo 2004, Stuart-Smith and Hayes

2003, White et al. 1999). Nest predation rates have not been found to be correlated to any

type of forest management (Brawn et al. 2001, King and DeGraaf 2000, King et al. 1998,

Stuart-Smith and Hayes 2003) however; predation rates are higher closer to edge than the

interior forest (King et al. 1998). Because nest predation is related to edge, silvicultural

treatments that produce more edge (i.e., group selection cuts) have the potential for

greater impact on the avian community (King et al. 1998).

Home Range Size

An animal’s home range, as defined by Burt (1943), is “that area traversed by the

individual in its normal activities of food gathering, mating, and caring for young.” A

birds’ territory is the area that he overtly defends from conspecifics (Wilson 1979). The

home range differs from the territory in that it may contain areas that the bird uses, but

does not defend as his own. For birds, breeding home ranges and territories provide

resources for nesting and fledging young. Historically most research has been able to

report on territory size, but due to recent developments in smaller radio transmitters,

analyzing home range has become a viable option.

Home range size varies in differing habitat quality levels, with poor quality

habitat resulting in the need for a larger home range and subsequently in a lower bird

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density at a site (Mazarolle and Hobson 2004). Home range size and quality can be

influenced by a variety of factors, including the availability of nest sites, perch sites, and

foraging areas; food abundance; predator abundance; bird density; competition with

conspecifics; and age and size of the bird (Fretwell and Lucas 1970, Mazarolle and

Hobson 2004, Petit and Petit 1996, Smith and Shugart 1987, Wilson 1979). The role of

these factors in home range and habitat selection has long been a focus in avian ecology.

The ideal dominance model of habitat selection states that dominant individuals

occupy optimal habitat and subordinates are forced to occupy lower quality habitat or to

not defend a territory at all (Fretwell and Lucas 1970). Mazarolle and Hobson (2004)

found that older and larger ovenbirds (Seiurus aurocapillus Linnaeus) had larger

territories than smaller and younger males, thus supporting the model. The older males

also had more exclusive territories with fewer overlaps. Older and larger prothonotary

warblers (Protonotaria citrea Boddaert) occupy higher quality habitats than subordinate

males (Petit and Petit 1996). Older males arrive on the breeding grounds earlier than

younger males, so prime habitat is often ‘claimed’ before younger males arrive (Petit and

Petit 1996). Smith and Moore (2005) found that American redstart (Setophaga ruticilla

Linnaeus) males that arrived on the breeding grounds earlier appeared to settle on higher

quality territories and hatched nestlings earlier, while females began their clutches earlier

and produced heavier nestlings than later arrivals. The model assumes that fitness at high

population levels is lowered by some other mechanism, such as resource abundance or

predation risk. Forest management has the potential to alter the mechanisms which affect

the ideal dominance model.

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The food-value theory states that birds defend territories to have sufficient

resources to raise offspring (Wilson 1979). Many studies concur that territory size is

related to the abundance of prey availability (Marshall and Cooper 2004, Nagy and

Holmes 2005, Petit and Petit 1996, Smith and Shugart 1987). There are three hypotheses

that imply different mechanisms by which territories and prey abundance are related

(Smith and Shugart 1987). The first is the direct-monitoring hypothesis, which states that

individuals directly monitor prey abundance and adjust territory size, thereby insuring

sufficient resources. This hypothesis has been rejected because territory size appears to

be relatively constant during the breeding season, whereas prey abundance is not

(Marshall and Cooper 2004). With the second hypothesis, an individual defends an area

as large as possible, but territory size is limited by intra-specific competition for habitat

(intra-specific competition hypothesis). The third hypothesis, the structural cues

hypothesis, states that territory size is a function of expected prey abundance based on

habitat structure. The latter two hypotheses are consistent with and complement each

other. If the structural cues hypothesis is true, it explains how birds acquire information

about resource abundance within an area, thus explaining the cause of competition

intensity at a site (Smith and Shugart 1987). Marshall and Cooper (2004) found that food

abundance fluctuated unpredictably over the course of the breeding season and among

territories, although territory sizes remained relatively constant. They also found that

territory size of red-eyed vireos (Vireo olivaceus Linnaeus) was correlated with the

foliage density at the time the territory was established. Foliage density was correlated

with food abundance at the nestling stage, demonstrating a link between foliage density,

food abundance, and territory size. This suggests that birds are using foliage density as an

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indicator of food abundance at the most critical point in the nesting cycle (the nestling

stage). Smith and Shugart (1987) also found an inverse relationship between territory size

and expected prey abundance (based on habitat structure). They suggest a habitat quality

gradient that is defined by relationships between habitat structure and prey abundance

which influence variation in territory size. Since forest management affects foliage

density and habitat structure, it is important to understand how management will alter

resources available to birds.

Importance of the study

Much research of avian responses to forest disturbance has focused on avian

species richness and abundance (Blake 2005, Chambers et al. 1999, Davis et al. 2000,

Harrison and Kilgo 2004, Stanton 1986), but richness and abundance are not necessarily

good indicators of habitat quality since they do not necessarily reflect individual fitness

(Van Horne 1989, Vickery et al. 1992a). To understand how and why forest disturbance

affects avian ecology, the mechanisms that cause these changes must be evaluated

(Marzluff et al. 2000). Results from early studies of avian response are often inconsistent

and too simplified because of difficulties in conducting large-scale ecological research in

“true” experimental and replicated fashion (Marzluff et al. 2000).

My research addresses many of these issues because (1) it was a manipulative

experiment so that the treatment conditions were randomly assigned to selected forest

stands within logistical limitations, (2) I collected data before and after treatments so that

treatment effect could me more accurately estimated, (3) each treatment was replicated

three times so that the treatment effects could be relatively precisely estimated, and (4) I

examined both the general bird community structure and responses as well as parameters

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such as home range size, habitat selection, and reproductive success index which are

closely related to individual bird fitness.

Bibliography

Alterman, L.E., J.C. Bednarz, and R.E. Thill. 2005. Use of group-selection and seed-tree

cuts by three early-successional migratory species in Arkansas. Wilson Bulletin

117: 353-363.

Artman, V.L. and J.F. Downhower. 2003. Wood Thrush (Hylocichla mustelina) nesting

ecology in relation to prescribed burning of mixed-oak forest in Ohio. The Auk

120: 874-882.

Artman, V.L., E.K. Sutherland, and J.F. Downhower. 2001. Prescribed burning to

restore mixed-oak communities in southern Ohio: Effects on breeding-bird

populations. Conservation Biology 15: 1423-1434.

Askins, R.A. 2001. Sustaining biological diversity in early successional communities: the

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14

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15

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16

CHAPTER 2

MICROCLIMATE, MICROHABITAT, AND BIRD COMMUNITY CONDITIONS

BEFORE FOREST STAND TREATMENT

Introduction

Forest ecosystems on the Cumberland Plateau provide habitat for a vast number

bird species, some of which have experienced population declines over the last four

decades (Askins et al. 1990, James et al. 1996). The US Department of Agriculture

Forest Service focus has shifted from primarily timber production in the early 1900s to

more focus on ecosystem management, biodiversity, and species viability from the late

1900s to the present (Quigley 2005). More emphasis on managing for healthy

ecosystems has heightened interest in identifying causal relationships between wildlife

and habitat. Understanding these relationships is imperative to understand declines in

bird populations. Recent research on effects of timber harvest on bird populations have

generally been short-term, unreplicated, and correlative (Sallabanks et al. 2000,

Thompson et al. 2000). It has been recommended that to be more useful, future research

should incorporate hypothesis testing, manipulative experiments, data collection on both

pre-and post-treatment conditions, and evaluate the causal relationships underlying

changes in bird communities (Anderson et al. 2001, Brawn et al. 2001, Marzluff et al.

2000, Sallabanks et al. 2000, Thompson et al . 2000). Pretreatment data is especially

17

helpful because it allows the researcher to evaluate the magnitude of change in addition

to differences among treatments.

The objective of this portion of the study was to quantify the bird community,

microhabitat characteristics, and microclimate in eighteen study plots scheduled for

silviculture treatment (treatments scheduled within the following two years). I explored

the relationships between the bird community and microhabitat, and tested the null

hypothesis that there is no difference in any of the collected variables among the eighteen

stands prior to treatment.

Study Area and Methods

Study Area

The study was located in the northern third of William B. Bankhead National

Forest (Fig. 2.1), located in Lawrence and Winston counties, northwestern Alabama.

Bankhead National Forest (BNF) is a 72,800 ha multi-use forest located in the strongly

dissected plateau subregion of the southern Cumberland Plateau (Smalley 1979). Soils

are dominated by Hartsells, Linker, Nectar, Wynnville, Albertville, and Enders soil types.

Slopes are gentle and drainage is good (Smalley 1979). The forests in this region have a

diverse species composition due to a variety of past disturbances – agriculture in the

1800s, heavy cutting and wildfire in the early 1900s, fire suppression in the last decade

and the recent large scale infestations of the southern pine beetle (Dendroctonus frontalis

Zimmerman) (Gaines and Creed 2003). In the 1930’s, abandoned farm land and other

open lands were reestablished with loblolly pine, Pinus taeda Linnaeus (Gaines and

Creed 2003). This has resulted in 31,600 ha of loblolly pine throughout BNF. Once

18

established, intensive pine plantation management was not implemented, and

subsequently, a variety of hardwood species voluntarily invaded the sites. Over the past

decade, southern pine beetle infestations have killed a major portion of loblolly pine,

increasing fuel loads and the risk of wildfires (Gaines and Creed 2003). Bankhead

National Forest has initiated a Forest Health and Restoration Project to promote healthy

forest growth via thinning and fire disturbance. The thinning and fire prescriptions were

administered to return the forest to a mixed oak-pine upland ecosystem. My research was

conducted in conjunction with BNF’s restoration project.

Pretreatment data were collected from eighteen research stands located on upland

sites composed of 20 to 35 year old loblolly pine. Stands were comprised of a minimum

of sixty percent pine (loblolly pine or Virginia pine, P. virginiana Mill.), with the

remainder mainly oak species. Average stand size was 12 ha and stands had similar age

and stand density. Pre-treatment data were collected between April and August 2005.

Figure 2.1. Location of study plots in Bankhead National Forest, AL.

19

Sampling

Microclimate. I used Hobo dataloggers (Onset Corp., Bourne, MA) to collect

microclimate data. One data logger was placed in each stand and recorded ambient

temperature (oFahrenheit) and relative humidity every four hours from May 15 – July 11,

2005. Each data logger was attached to the top of a wooden stake and protected by a 1

liter plastic container with the bottom removed to allow for access and ventilation.

Microhabitat. I performed line transect habitat surveys at the end of the breeding

season (July – August 2005) to assess the microhabitat within each stand. Placement of

three habitat plots was determined by a random compass bearing and distance (30 – 50

m) from a central point in the stand. Two 20 m perpendicular transects placed north-

south and east-west from the center of the habitat plot formed the structure for the survey.

I recorded presence or absence of the following parameters at 0.5 m intervals along each

transect: litter, bare ground, herbaceous cover, and woody cover. I measured litter depth

(to nearest mm) at the center point and at 2 m intervals along each transect. At 5 m

intervals, I recorded percent canopy cover (using a convex spherical densitometer, to

nearest percent) and the presence of each vertical forest layer. Vertical forest layers were

assigned a value of 1-4, with the following designations: 1) ground cover (< 2 m); 2)

understory (> 2 m - < 4 m); 3) mid-story (> 4 m - < 6 m); and 4) overstory (>6 m) (FIA,

1998). Forest level 4 was approximately 14 m high.

Additional forest characteristics (basal area, tree species richness, and tree

abundance) were calculated from data collected by the USDA Forest Service Southern

Research Station (provided by Callie Schweitzer). These data were collected at five 0.08

ha circular plots systematically arranged within each stand. The species and diameter at

20

breast height (DBH) of all trees greater than 14.2 cm DBH were recorded to the nearest

tenth of an inch using a diameter tape.

Bird Sampling. I sampled the bird community using line-transect surveys and

distance sampling methods (Buckland et al. 2001). Line transects were established on

each of the stands and flagged every 25 m. Each transect was 50 m from the edge of the

stand and 100 m wide; the observer slowly walked down the middle of the transect and

recorded all birds heard or seen within 50 m on either side. The observer recorded the

following: species, sex, age, the location of the bird in relation to the transect.

All stands were surveyed three times during the 2005 breeding season (15 May –

30 June) between 530 and 1030 Central Standard Time. Surveys were done in random

order and the transects walked in a different order at each visit. I conducted all surveys to

avoid observer bias.

Data Analysis

Microclimate data collected concurrently from all stands were used for

comparisons. Each 24-hour period was divided into day and night time periods (daytime

= 6:00, 10:00, 14:00; nighttime = 18:00, 22:00, 2:00), and variables included in the

analysis were mean day and night time air temperature and relative humidity. I averaged

microhabitat characteristics for the three habitat plots in each stand for comparison. I

calculated average basal area (BA) for the five tree plots using the equation 2.1. Basal

area was calculated in English measurements and then converted to metric. I inspected all

microclimate and microhabitat variables for normality visually and statistically using a

)144)(4(

2dBA

(Eq. 2.1)

21

Shapiro-Wilks tests. Nighttime May air temperature, nighttime June relative humidity,

canopy cover, forest level four, litter ground cover, herbaceous ground cover, woody

ground cover, and litter depth variables were log transformed to meet normality

assumptions. I used principle components analysis (PCA, SPSS v.15.0) to group the

original variables.

To create a relative bird abundance index, I divided the number of detections by

the transect length for each stand. Stands differed in size and shape and transect lengths

differed among stands as well. I used the greatest number of individuals detected among

the three surveys to estimate the relative abundance of each species. I grouped species

into four guilds based on their migration patterns (Sauer et al. 1996, Imhof 1976), nesting

location (Ehrlich et al. 1986), foraging location (Ehrlich et al. 1986) and habitat

association (Blake and Karr 1987, Freemark and Collins 1992) (Table 2.1). To evaluate

similarity among stands, I calculated Morisita’s similarity index. Morisita’s index is

recommended as the best overall measure of similarity for ecological use (Magurran

1988). The index ranges from 0 to 1, with 0 representing pairs of sites with no species in

common and values of 1 representing complete overlap in species between sites. I used

the Shannon-Weiner diversity index, evenness, and species richness to describe the

community in each stand (Krebs 1998). To standardize species richness because transect

lengths differed among plots, I used rarefaction (Krebs 1998). I inspected all variables

for normality visually and statistically using Shapiro-Wilks tests and log transformed the

following variables to better meet normality assumptions: diversity, cavity nesting guild

abundance, foliage foraging guild abundance, and edge/open guild abundance.

22

Table 2.1. Guild memberships of songbird species detected on eighteen upland pine-hardwood stands in Bankhead National Forest,

AL, classified by: forage guild (A, aerial; F, foliage; G, ground, B, bark) (Ehrlich et al. 1986), nest location (G, ground; S, shrub; T,

tree; C, cavity) (Ehrlich et al. 1986), migratory destination (N, Neotropical migrant; T, temperate migrant; R, resident) (Sauer et al.

1996, Imhof 1976), and habitat association (O/E, open-edge; I/E, interior-edge; I, interior) (Blake and Karr 1987, Freemark and

Collins 1992).

Species Nesting Migration Habitat Forage

Code Common Name Scientific Name Guild Guild Guild Guild

ACFL Acadian Flycatcher Empidonax virescens Vieillot T N I A

BAWW Black-and-White Warbler Mniotilta varia Linnaeus G T I B

BGGN Blue-gray Gnatcatcher Polioptila caerulea Linnaeus T T I/E F

BHCB Brown-headed Cowbird Mothorous ater P R O/E G

BHVI Blue-headed Vireo Vireo solitarius Wilson T N I/E F

BLGR Blue Grosbeak Guiraca caerulea Linnaeus S N O/E G

BLJA Blue Jay Cyanocitta cristata Linnaeus T R I/E G

BRTH Brown Thrasher Toxostoma rufum Linnaeus S T O/E G

BTGW Black-throated Green Warbler Dendroica virens Gmelin T N I F

CACH Carolina Chickadee Poecile carolinensis Audubon C R I/E F

CARW Carolina Wren Tryothorus ludovicianus Latham C R O/E G

DOWO Downy Woodpecker Picoides pubescens Linnaeus C R I/E B

ETTI Eastern Tufted Titmouse Baeolophus bicolor Linnaeus C N I/E F

GCFL Great Crested Flycatcher Myiarchus crinitus Linnaeus C R I/E A

HAWO Hairy Woodpecker Picoides villosus Linnaeus C N I B

HOWA Hooded Warbler Wilsonia citrina Boddaert S N I F

INBU Indigo Bunting Passerina cyanea Linnaeus S N O/E F

KEWA Kentucky Warbler Oporornis formosus Wilson G N I/E G

LOWA Louisiana Waterthrush Seiurus motacilla Vieillot G R I/E G

NOCA Northern Cardinal Cardinalis cardinalis Linnaeus S R I/E G

NOMO Northern Mockingbird Minus polygottos Linnaeus S T E G

NOPA Northern Parula Parula Americana Linnaeus T N I/E F

OVEN Ovenbird Seiurus aurocapillus Linnaeus G R I F

PIWA Pine Warbler Dendroica pinus Wilson T R I/E B

PIWO Pileated Woodpecker Dryocopus pileatus Linnaeus C T I B

22

23

Species Nesting Migration Habitat Forage

Code Common Name Scientific Name Guild Guild Guild Guild

PRWA Prairie Warbler Dendroica discolor Vieillot S N O/E F

RBWO Red-bellied Woodpecker Melanerpes carolinus Linnaeus C R I/E B

REVI Red-eyed Vireo Vireo olivaceus Linnaeus S N I/E F

SCTA Scarlet Tanager Piranga olivacea Gmelin T N I F

SUTA Summer Tanager Piranga ruba Linnaeus T R I/E F

WBNU White-breasted Nuthatch Sitta carolinensis Latham C T I B

WEVI White-eyed Vireo Vireo griseus Boddaert S N O/E F

WEWA Worm-eating Warbler Helmitheros vermivorus Gmelin G N I F

WOTH Wood Thrush Hylocichla mustelina Gmelin T N I/E G

YBCH Yellow-breasted Chat Icteria virens Linnaeus S N O/E F

YBCU Yellow-billed Cuckoo Coccyzus americanus Linnaeus T N I/E F

23

24

I used analysis of variance (ANOVA) with treatment and block as main factors to

test for differences among stands in bird community, microclimate, and microhabitat

PCs. Tukey’s multiple comparisons test was performed based on results of the ANOVA.

All analyses were performed in SPSS (v.15.0) using an alpha level of 0.05.

To investigate variation in abundance of species and guilds as they relate to

microhabitat measures, I used canonical correspondence analysis (CCA, CANOCO

v.4.5). I used only species that had greater than five detections in the analysis so that rare

species would not bias the results. This procedure is a direct gradient analysis technique

that compares community composition directly to environmental variables across a

gradient (Palmer 1993). CCA is appropriate to use when there are no differences among

stands because it evaluates gradients on a different scale; it examines the trends and

variability within stands.

Results

Microclimate. There were no differences in microclimate characteristics among

stands (p > 0.05). Temperature and relative humidity increased over the season on all the

plots (Table 2.2)

The original twelve variables showed low multivariate correlation (Kaiser-Meyer-

Olkin [KMO] Measure of Sampling Adequacy = 0.355) so the three variables with the

lowest multivariate correlation (nighttime July temperature, nighttime July relative

humidity, and nighttime May temperature) were removed from the PCA to increase the

KMO measure of sampling adequacy to 0.55. The remaining 9 variables were grouped

into 3 principle components (PCs), the first representing daytime climate, the second

25

Table 2.2. Mean microclimate and standard error for microclimate characteristics in

upland pine-hardwood stands before treatment in Bankhead National Forest, AL, 2005.

Month and Time Degrees Celsius Relative Humidity

May Day 20.6 ± 0.6 65.1 ± 2.1

May Night 17.9 ± 0.5 73.1 ± 2.5

June Day 23.5 ± 0.5 76.1 ± 2.1

June Night 21.2 ± 0.4 84.1 ± 2.4

July Day 24.2 ± 0.9 80.1 ± 2.7

July Night 22.1 ± 0.8 86.7 ± 1.6

26

representing nighttime climate, and the third representing temperature (Table 2.3). The 3

components retained approximately 92 % of the original variation (Bartlett’s Test of

Sphericity χ2 = 195.209, df = 36, p = 0.000).

Microhabitat. There was no difference in microhabitat among the stands (p > 0.05).

Plots were characterized by high litter ground cover, high percent canopy cover, and a

high presence of forest level four (Table 2.4).

The original twelve variables were grouped into 4 principle components (PCs), the

first representing understory cover and forest structure, the second representing canopy

cover, the third representing BA, and the fourth representing litter depth (Table 2.5). The

4 components retained approximately 79% of the original variation (Bartlett’s Test of

Sphericity χ2 = 103.832, df = 66, p = 0.002).

Bird Community. A total of 1185 birds were detected, representing 35 species (Table

2.1). The most abundant species were the red-eyed vireo (Vireo olivaceus Linnaeus),

comprising 20.9% (249 detections) of total individuals, and the pine warbler (Dendroica

pinus Wilson), comprising 11.6% (138 detections) of total individuals. The majority of

the community comprised bids in the following guilds: shrub nesting, Neotropical

migrant, and interior/edge habitat specialist (Table 2.6). There were significantly more

aerial foraging birds on the plots to be burned than those to be thinned and more

interior/edge. Morisita’s similarity indices indicate that species composition on all stands

were similar to one another (Table 2.8).

The bird community included twelve species that are listed in Partners in Flight’s

(PIF) North American Landbird Conservation Plan as Species of Continental Importance

(Rich et al. 2004, Table 2.7). PIF lists species in two categories; WatchList species are

a.

27

Table 2.3. Principle component analysis loadings, eigenvalues, and percent variance

for microclimate variables on uplandpine-hardwood stands in Bankhead National Forest,

AL, 2005.

PC1 PC2 PC3

Daytime May Temperature 0.907

Daytime June Temperature 0.923

Daytime July Temperature 0.604 0.727

Daytime May RelHumdity -0.838 0.372 0.332

Daytime June RelHumdity -0.662 0.592 0.339

Daytime July RelHumdity -0.904

Nighttime June Temperature -0.603 0.754

Nighttime May RelHumdity 0.946

Nighttime June RelHumdity 0.346 0.921

Eigenvalue 4.18 2.66 1.43

% Variance 46.49 29.56 15.87

28

Table 2.4. Means for microhabitat characteristics on upland pine-hardwood stands in

Bankhead National Forest, AL, 2005.

Microhabitat Characteristic Mean ± SE

Ground cover: Percent litter 99.4 ± 0.7

Ground cover: Percent herbaceous plants 16.9 ± 13.2

Ground cover: percent woody plants 11.0 ± 7.6

Litter depth (cm) 6.3 ± 1.0

Percent canopy cover 82.5 ± 6.8

Forest level 1 present 20.7 ± 5.8




29

Table 2.5. Principle component analysis loadings, eigenvalues, and percent

variance for microhabitat variables on upland pine-hardwood stands in

Bankheand National Forest, AL, 2005.

PC1 PC2 PC3 PC4

Herb Cover 0.885

Woody cover 0.857 0.337

Canopy Cover 0.663 -0.617

Litter Cover 0.788

Litter Depth -0.379 -0.381 0.688

Forest Level 1 0.819

Forest Level 2 0.528 0.539

Forest Level 3 -0.376 -0.772 0.336

Forest Level 4 0.406 0.780

Basal Area -0.439 -0.743

Tree Species Richness 0.760 0.380

Tree Abundance -0.859

Eigenvalue 4.50 2.25 1.51 1.18

% Variance 37.50 18.73 12.62 9.86

30

Table 2.6. Significance value, mean, and standard error by proposed treatment for bird

community on upland pine-hardwood stands in Bankhead National Forest, AL, 2005.

Superscript letters indicate differences among means in the same row (Tukey test p

<0.05).

Means by treatment

Community

Variable p Control

To be

burned

To be

thinned

To be

thinned/burned

Species rich. 0.24 12.45±0.39 12.39±1.66 13.30±0.63 14.54±0.56

Relative

abundance 0.24 99.57±3.16 99.08±13.28 106.38±5.05 116.34±4.47

Div. index 0.32 2.45±0.53 2.39±0.23 2.55±0.04 2.64±0.05

Evenness 0.06 0.90±0.02 0.87±0.03 0.95±0.10 0.92±0.01

Nesting Guild

Tree 0.06 11.29±2.73 11.85±1.64 11.13±1.65 17.41±1.43

Shrub 0.31 10.65±3.19 13.73±2.90 16.04±2.81 17.51±2.34

Ground 0.82 5.91±2.15 5.26±2.44 7.81±1.95 6.30±1.42

Parasite 0.29 0±0 0±0 0.17±0.17 0.50±0.22

Cavity 0.07 6.85±1.33 5.05±1.58 7.32±1.07 12.22±2.49

Foraging Guild

Foliage 0.05 24.35±3.43 22.78±3.75 27.05±4.83 36.87±5.05

Aerial 0.02 1.82±0.57ab

2.16±1.38a 0.75±0.15

b 2.90±0.20

ab

Ground 0.45 3.11±0.89 4.38±1.73 4.36±0.98 5.79±0.73

Bark 0.65 6.80±2.17 6.57±1.33 8.17±1.18 8.72±1.38

Migration Guild

Neotropical 0.07 19.80±2.60 21.49±4.34 24.78±3.99 31.07±2.78

Temperate 0.95 3.95±0.91 3.10±1.58 3.26±0.71 19.83±2.09

Resident 0.06 12.05±2.64 11.30±2.13 14.41±1.96 19.83±2.09

Habitat Guild

Interior 0.55 12.33±3.15 9.30±3.70 15.03±4.34 16.10±2.28

Interior/edge 0.03 17.74±2.84a 23.80±3.38

ab 22.34±2.25

ab 30.72±2.44

b

Edge/open 0.24 2.83±1.26 2.84±1.14 4.47±0.64 6.90±2.21

31

Table 2.7. Species of Continental Importance, as listed by the Partners in Flight

Landbird Conservation Plan (Rich et al. 2004), detected on eighteen upland pine-

hardwood stands in Bankhead National Forest, AL, 2005. See Table 2.1 for scientific

names.

Species PIF Listing* Individuals Plots

Acadian Flycatcher S 7 8

Brown Thrasher S 1 1

Carolina Wren S 15 11

Hooded Warbler S 52 13

Indigo Bunting S 38 16

Kentucky Warbler W 6 6

Louisiana Waterthrush S 1 1

Pine Warbler S 80 18

Prairie Warbler W 5 5

White-eyed Vireo S 5 4

Worm-eating Warbler W 53 15

Wood Thrush W 2 1

* S = Stewardship Species, W = WatchList Species (Rich et al. 2004)

32

Table 2.8. Morisita’s similarity index for the breeding bird community on eighteen

upland pine-hardwood stands in Bankhead National Forest, AL, 2005.

treatment control

To be

burned

To be

thinned

To be

thinned/burned

Control -- 0.97 1.04 1.06

To be Burned 0.97 -- 1 1

To be thinned 1.04 1 -- 1.04

To be thinned/burned 1.06 1 1.04 --

33

species that have multiple reasons (restricted distribution, low population size,

widespread population declines, high threats to habitat, etc.) for conservation concern the

variation in the first three axes. Axis one explained 33.1% (Eigenvalue = 0.023), the

second axis 20.1% (Eigenvalue = 0.014), and the third 14.8% (Eigenvalue = 0.010).

The CCA of microhabitat characteristics and species abundance revealed a gradient

of microhabitat characteristics evident by the position of variables along the axes of the

ordination plots (Fig. 2.2). On one end of the gradient is canopy cover and tree

abundance, on the other is percent woody ground cover, percent herbaceous ground

cover, presence of forest level one, and tree species richness. The Kentucky warbler

(Oporornis formosus Wilson), hooded warbler (Wilsonia citrina Boddaert), worm-eating

warbler (Helmitheros vermivorus Gmelin) were strongly associated with the presence of

woody and herbaceous ground cover (Fig. 2.2). The blue jay (Cyanocitta cristata

Linnaeus) was associated with tree abundance (Fig. 2.2), the white-eyed vireo (Vireo

griseus Boddaert) with the presence of forest level one (Fig. 2.2), and the Carolina wren

(Tryothorus ladovicianus Latham) with litter depth (Fig. 2.2).

The CCA of microhabitat characteristics and nesting guild associations revealed a

similar gradient, ranging from canopy cover and presence of forest level three on one end

of the gradient to herbaceous ground cover, woody ground cover and presence of forest

level one on the other (Fig. 2.3). A second gradient was also evident, one end with basal

area, litter depth, and presence of forest level four and at the other end, presence of forest

level two (Fig. 2.3). The nesting guilds were evenly distributed across the ordination.

The shrub nesting guild was associated with the presence of forest level one and two, and

a high percentage of woody and herbaceous ground cover (Fig. 2.3). Ground nesting

34

.

Figure 2.2. First and second canonical correspondence axes for bird species and

microhabitat variables, Bankhead National Forest, AL. See table 2.1 for species code

explanations

35

.

Figure 2.3. First and second canonical correspondence axes for nesting guild associations and

microhabitat variables, Bankhead National Forest, AL, 2005

36

species were also associated with a high percentage of woody and herbaceous ground

cover, and the presence of forest level two (Fig. 2.3). Tree nesting species were

associated with high canopy cover and the presence of forest level three (Fig. 2.3).

Cavity nesting species appear to be associated with basal area and litter depth (Fig. 2.3).

The CCA of microhabitat characteristics and foraging guild associations revealed a

gradient from understory to overstory cover. On one end of the gradient was the presence

of forest level one, two, and four, tree species richness, and woody and herbaceous

ground cover; on the other end was canopy cover, litter ground cover, litter depth, and the

presence of forest level three (Fig. 2.4). In the center of the plot was foliage foraging

species, indicating that they are more generalist species. On the far edge of the plot was

aerial feeding species, associated with BA (Fig. 2.4). Bark foraging species showed an

association with the presence of forest level three and ground foraging species showed an

association with canopy cover and litter ground cover (Fig. 2.4).

Discussion

The overall structure of the bird and forest community before treatment appears to

be a mid-successional forest. Forest structure was defined by high percentage of canopy

cover and also a high presence of understory vegetation. The bird community consisted

of a majority of shrub nesting species and interior/edge dwelling species. Optimal habitat

for these guilds was created by the presence of wildlife openings, roads, and southern

pine beetle damaged areas within many of the plots, which create small pockets of open

areas and increase the amount of edge. All stands were similar to one another in terms of

microhabitat and microclimate characteristics, although there were differences in some

37

Figure 2.4. First and second canonical correspondence axes for foraging guild associations and

microhabitat variables, Bankhead National Forest, AL, 2005.

38

aspects of the bird community among the stands. Knowing these differences will give

insight when evaluating post-treatment data.

The bird community included no federally listed species; however twelve species

of continental importance were detected on the stands, including four species listed on the

PIF WatchList. These are relatively abundant species that have multiple reasons for

conservation concern (Rich et al. 2004). Many of the species of concern found on the

stamds are disturbance-dependent shrub- or ground-nesting species (brown thrasher

[Toxostoma rufum Linnaeus], hooded warbler, indigo bunting [Passerina cyanea

Linnaeus], Kentucky warbler, prairie warbler [Dendroica virens Vieillot], and white-eyed

vireo), which represents the major habitat type of conservation concern in the eastern US

(Rich et al. 2004).

Bird abundance and nesting guild abundance were related to the gradient of

microhabitat characteristics occurring on the plots. The distribution of birds along this

gradient corresponds with what is known about the natural history of the animals.

Species that forage and nest in the understory (Kentucky warbler, hooded warbler, worm-

eating warbler) were strongly associated with the presence of woody and herbaceous

ground cover. The presence of ground cover would provide both cover and nesting

habitat for theses species. The white-eyed vireo, an edge-associated species, was

associated with the presence of forest level one. Forest level one was part of the gradient

from high canopy cover percentage to low canopy cover percentage, so an indication of

the presence of forest level one also indicates a lower amount of canopy cover. The

ordination plot shows an association between blue jays and tree abundance, which may

just be a random occurrence due to the low number of detections (n=9).

39

The distribution of nesting guild abundance along the gradients indicates a

distinct separation of habitat suitable for each guild. Ground and shrub nesting species

were associated with high percent of ground cover and the presence of forest level two,

which would be the primary source of cover and nesting habitat for these species. Tree

nesting species were associated with high canopy cover and the presence of forest level

three, again this would be the primary source of cover and nesting habitat for these

species. The association between cavity nesting species and litter depth and basal area

does not make sense. Cavity nesting guild species are made up of both primary (i.e.,

woodpeckers) and secondary (i.e., eastern tufted titmouse [Baeolophous bicolor

Linnaeus], Carolina wren) cavity nesters. There could be a relationship between the

volume of trees (basal area) and the number of snags present or the number of cavities

available for secondary nesting species; however none of the microhabitat characteristics

that we measured appears to explain the variation in the abundance of cavity nesting

species.

Bibliography

Anderson, D.R., W.A. Link, D.H. Johnson, K.P. Burnham. 2001. Suggestions for

presenting the results of data analyses. Journal of Wildlife Management 65: 373-

378.

Askins, R.A., J.F. Lynch, and R. Greenberg. 1990. Population declines in migratory

birds in eastern North America. Current Ornithology 7:1-57.

Blake, J.G. and J.R. Karr. 1987. Breeding birds of isolated woodlots: area and habitat

relationships. Ecology 68:1724-1734.


the ecology and conservation of birds. Annual Review of Ecological Systems 32:

251-276.

40

Buckland, S. T., D. R. Anderson, K. P. Burnham, J. L. Laake, D. L. Borchers, and L.

Thomas. 2001. Introduction to distance sampling. Oxford University Press,

Oxford.

Ehrlich, P.R., D.S. Dobkin, and D. Wheye. 1988. The birder’s handbook: a field guide

to the natural history of North American birds. Simon and Schuster, New York,

NY. 785 pp.

FIA. 1998. Field instructions for southern forest inventory. Remeasurement of prism

plots. Southern Research Station, Forest Service, U.S. Department of Agriculture.

Item 26 version of manual.

Freemark, K. and B. Collins. 1992. Landscape ecology of birds breeding in temperate

forest fragments. Pp. 443-454 in Ecology and Conservation of Neotropical Migrant

Landbirds (J.M. Hagen III and D.W. Johnston, eds.). Smithsonian Institution Press,

Washington, D.C.

Gaines, G.D. and J.W. Creed. 2003. Forest health and restoration project. National

forests in Alabama, Bankhead National Forest Franklin, Lawrence and Winston

Counties, Alabama. Final environmental impact statement. Management Bulletin

R8-MB 110B.

Imhof, T.A. 1976. Alabama birds. The University of Alabama Press, University, AL.

445 pp.

James, F.C., C.E. McCullough, and D.A. Wiedenfeld. 1996. New approaches to the

analysis of population trends in land birds. Ecology 77: 13-27.

Krebs, C.J. 1998. Ecological methodology. Addison Wesley Longman, Menlo Park,

CA. 620 pp.

Magurran, A.E. 1988. Ecological diversity and its measurement. Princeton University

Press, Princeton, NJ. 179pp.

Marzluff, J.M., M.G. Raphael, and R. Sallabanks. 2000. Understanding the effects of

forest management on avian species. Wildlife Society Bulletin 28: 1132-1143.

Palmer, M.W. 1993. Putting things in even better order: the advantages of canonical

correspondence analysis. Ecology 74: 2215-2230.

Quigley, T.M. 2005. Evolving views of public land values and management of natural

resources. Rangelands 27: 37-44.

Rich, T. D., C. J. Beardmore, H. Berlanga, P. J. Blancher, M. S. W. Bradstreet, G. S.

Butcher, D. W. Demarest, E. H. Dunn, W. C. Hunter, E. E. Iñigo-Elias, J. A.

41

Kennedy, A. M. Martell, A. O. Panjabi, D. N. Pashley, K. V. Rosenberg, C. M.

Rustay, J. S. Wendt, T. C. Will. 2004. Partners in Flight North American Landbird

Conservation Plan. Cornell Lab of Ornithology. Ithaca, NY.

Sallabanks, R., E.B. Arnett, and J.M. Marzluff. 2000. An evaluation of research on the

effects of timber harvest on bird populations. Wildlife Society Bulletin 28: 1144-

1155.

Sauer, J.R., S. Schwartz, and B. Hoover. 1996. The Christmas Bird Count Home Page.

Version 95.1, http://www.mbr-pwrc.usgs.gov/bbs/cbc.html. USGS Patuxent

Wildlife Research Center, Laurel, MD.

Smalley, G.W. 1979. Classification and evaluation of forest sites on the Southern

Cumberland Plateau: U.S. Department of Agriculture, Forest Service, Southern

Forest Experiment Station, general technical report SO-23.

Thompson, F.R., III, J.D. Brawn, S. Robinson, J. Faaborg, R.L. Clawson. 2000.

Approaches to investigate effects of forest management on birds in eastern

deciduous forests: How reliable is our knowledge? Wildlife Society Bulletin 28:

1111-1122.

42

CHAPTER 3

MICROHABITAT, MICROCLIMATE, ARTHROPOD AVAILABILITY, AND BIRD

COMMUNITY IN FOREST STANDS TREATED WITH BURNING AND THINNING

Introduction

The decline of Neotropical migratory songbirds in eastern North America has

been a subject of much discussion among ornithologists over the past two decades

(Askins et al. 1990, Finch 1991, James et al. 1996, Rappole and McDonald 1994,

Robbins et al. 1989). Although some evidence of declines is conflicting, it is generally

accepted that due to general trends of habitat loss or degradation, and their importance to

the ecosystems, giving priority conservation status to Neotropical songbirds is justified.

In recent studies, the decline of birds associated with early successional breeding habitat

has been noted (Askins et al. 1990, Hunter et al. 2001, Litvaitis et al. 1999). Trani et al.

(2001) reported that, according to Forest Inventory and Analysis (FIA) data, young forest

habitats are declining due to forest maturation and the absence of timber removal on

much public land. Tree removal creates early successional habitat by removing trees to

create an environment favorable for tree growth or regeneration (Smith et al. 1997). As

forest management evolves to employ multiple silvicultural tools to meet a myriad of

objectives, it is important to understand how such management affects the bird

community and if quality early successional wildlife habitat is produced.

43

Prescribed burning has garnered heightened awareness on public lands as a

silvicultural technique since fire suppression in eastern forests has been questioned

(Brose et al. 2001, Van Lear and Waldrop 1989). Although the effect of silviculture and

fire on birds has been studied individually in eastern forests, there is little research

assessing the effect of thinning and prescribed burning (Greenberg et al. 1995, Greenberg

et al. 2007) and only one study reports the effects when tree reduction and burning are

combined (Wilson et al. 1995). It is important to understand how these treatments will

affect the bird community when compared to other silvicultural techniques.

The objective of this portion of the study was to quantify the bird community,

microhabitat characteristics, microclimate, and arthropod availability on six silvicultural

treatments in the William B. Bankhead National Forest. I examined the change in

microhabitat and microclimate features after implementation of the silvicultural

treatments, explored the relationships between the bird community; and the structure and

features of microhabitat, microclimate, and arthropod availability and tested the null

hypothesis that there is no difference in any of the collected variables among the

treatments.


Study Area


Forest (Fig 3.1), located in Lawrence and Winston counties, northwestern Alabama.

Bankhead National Forest (BNF) is a 72,800 ha multi-use forest located in the Strongly

Dissected Plateau subregion of the southern Cumberland Plateau (Smalley 1979). Soils

44

are dominated by Hartsells, Linker, Nectar, Wynnville, Albertville, and Enders soil types.

Slopes are gentle and drainage is good (Smalley 1979). The forests in this region have a

diverse species composition due to a variety of past disturbances – agriculture in the

1800s, heavy cutting and wildfire in the early 1900s, fire suppression in the last decade

and the recent infestation of the southern pine beetle (Dendroctonus frontalis

Zimmerman) (Gaines and Creed 2003). In the 1930’s, abandoned farm land and other

open lands were reestablished with loblolly pine, Pinus taeda Linnaeus (Gaines and

Creed 2003). This has resulted in 31,600 ha of loblolly pine throughout BNF. Once

established, intensive pine plantation management was not implemented, and

subsequently, a variety of hardwood species voluntarily invaded these sites. Over the

past decade, southern pine beetle infestations have killed a major portion of loblolly pine,

increasing fuel loads and the risk of wildfires (Gaines and Creed 2003). Bankhead

National Forest has initiated a Forest Health and Restoration Project to promote healthy

forest growth via thinning and fire disturbance. The thinning and fire prescriptions were

administered to return the forest to a more healthy state and to promote regeneration of

native species. My research was conducted in conjunction with BNF’s restoration

project.

The study design consisted of a randomized complete block design with two

factors – three thinning levels (no thin, 11 m2 ha

-1 residual basal area, and 17 m

2 ha

-1

residual basal area) and two burn treatments (no burn and burn). Each treatment was

replicated three times and blocked by year. Treatments were assigned randomly to

45

Figure 3.1. Location of study plots in Bankhead National

Forest, Alabama.

Burning treatment

Burn No Burn

Control 3 3

Thin 6 6

Figure 3.2. Experimental design: two-factor, randomized

complete block design. Treatments include two burn

treatments and two thinning levels.

46

delineated stands. After the treatments were completed, I collapsed the thinned treatments

together because there was no difference in basal area between the two thinning levels (F

= 0.07, df = 1, p = 0.8). Although this was not the response variable I was studying, the

variability within individual treatment levels was uneven, with some stands within the

same treatment level having greater BA than the target and others having lower BA than

the target. This variation was too large to detect any difference between the thinning

levels. This created three replicates each of the control and burn, and six replicates each

of the thin and the thin/burn (Fig. 3.2). The research stands were located on upland sites

composed of 20 to 35 year old loblolly pine. Stands were comprised of a minimum of

sixty percent pine (loblolly pine or Virginia pine, P. virginiana Mill.), with the remainder

mainly oak species (Quercus spp.). Average stand size was 12 ha and plots had similar

age and stand density. Thinning favored the retention of hardwood species and was done

before fire prescriptions. Prescribed burning was completed in the dormant season

(January – March) with low-burning surface fires. Treatments on block one were

completed between August 2005 and 1 February 2006; blocks two and three were treated

between April 2006 and March 2007. Post- treatment data was collected from block one

between April and August 2006, and from blocks two and three between April and

August 2007. Post treatment data was collected in two different years, but because

treatments were blocked by year, any differences in year would be detected in the block

factor.

Sampling

47

Microclimate. Microclimate data were collected with Hobo dataloggers (Onset

Corp., Bourne, MA). One data logger was placed in each stand and recorded ambient

temperature (to tenth of a degree Centigrade [C]) and relative humidity every four hours

from May 15 – June 13. Each data logger was attached to the top of a wooden stake and

covered by a 1 liter plastic container with the bottom removed to allow for access and

ventilation.

Microhabitat. I performed line transect habitat surveys at the end of the breeding

season (July – August) to assess the microhabitat within each stand. Placement of three

habitat plots was determined during pre-treatment data collection by a random compass

bearing and distance (30 – 50 m) from a central point in the stand. The central point was

marked with a metal stake during pre-treatment data collection and the same distance and

compass bearing were used to locate post-treatment habitat plots. Two 20 m

perpendicular transects placed north-south and east-west from the center of the habitat

plot formed the structure for the survey. I recorded presence or absence of the following

parameters at 0.5 m intervals along each transect: litter, bare ground, herbaceous cover,

and woody cover. I measured litter depth (to nearest mm) at the center point and at 2 m

intervals along each transect. At 5 m intervals, I recorded percent canopy cover (using a

convex spherical densitometer, to nearest percent) and the presence of each vertical forest

layer. I assigned vertical forest layers a value of 1-4, with the following designations: 1)

ground cover (< 2 m); 2) understory (> 2 m - < 4 m); 3) mid-story (> 4 m - < 6 m); and 4)

overstory (>6 m) (FIA, 1998). I also recorded basal area (BA) at the center of each

habitat plot using a 10 factor basal area prism.

48

I calculated additional forest characteristics (basal area, tree species richness, and

tree abundance) from data collected by the USDA Forest Service Southern Research

Station (provided by Callie Schweitzer). These data were collected at five 0.08 ha

circular plots systematically arranged within each stand. The species and diameter at

breast height (DBH) of all trees greater than 14.2 cm DBH were recorded to the nearest

tenth of an inch using a diameter tape. All plots were marked with PVC pipe and trees

number tagged during pre- treatment data collection. The same plots and trees were re-

sampled post-treatment.

Arthropod availability. To sample the arthropod abundance in each stand, I used

the branch clipping method (Johnson 2000). Samples were collected at 50 m intervals

along each bird transect survey. A branch clip (approximately 25 cm), included the

terminal leaf cluster and was collected from either an oak or red maple (Quercus spp. and

Acer rubrum), alternating species at each sampling point. These two species were

selected because they are common hardwood species in the stand and commonly used for

foraging by songbirds. Each branch was randomly clipped from either 0-3 m or 3-6 m.

Each branch clip was collected using pruning sheers and collected in a white plastic

garbage bag. Once inside the bag, the leaves were sprayed with an insecticide to kill all

insects. After a minimum of 5 h, the leaves were removed from the bag, all arthropods

extracted, identified to Order, and lengths were measured to the nearest 0.05 cm. Each

branch was de-leafed, the leaves were air dried in paper bags, and the dry weight

recorded. Each stand was sampled monthly throughout the breeding season (April - July)

between 1200 h and 1600 h.

49

Bird Sampling. I sampled the bird community using line-transect surveys and

distance sampling methods (Buckland et al. 2001). Line transects were established on

each of the stands and flagged every 25 m. Each transect was 50 m from the edge of the

stand and 100 m wide; the observer slowly walked down the middle of the transect and

recorded all birds heard or seen within 50 m on either side. The observer recorded the

following: species, sex, age, the location of the bird in relation to the transect.

All stands were surveyed three times during the breeding season (15 May – 30 June)

between 530 and 1030 Central Daylight Savings Time. Surveys were done in random

order and the transects walked in a different order at each visit. I conducted all surveys to

avoid observer bias.

Data Analysis

Microclimate data collected concurrently from all stands were used for comparisons.

Each 24-hour period was divided into day and night time periods (daytime = 6:00, 10:00,

14:00; nighttime = 18:00, 22:00, 2:00), and variables included in the analysis were mean

day and night time air temperature and relative humidity. Data was lost (due to computer

crash) from three stands in block one. In these cases, the average from the remaining two

blocks was substituted for the lost data. I averaged microhabitat characteristics for the

three habitat plots in each stand for comparison. I calculated an average basal area for the

five tree plots using equation 3.1. Basal area was calculated in English measurements and

then converted to metric. I inspected all microclimate and microhabitat variables for

)144)(4(

2dBA

(Eq.3.1)

50

normality visually and statistically using a Shapiro-Wilks test. Daytime May relative

humidity and bare ground cover were square root transformed, litter cover was arcsine

transformed, and nighttime June temperature and tree species richness were log

transformed to meet normality assumptions. I used principle components analysis (PCA,

SPSS v. 15.0) to group the original variables.

Arthropod biomass was estimated based on length using regression models (SPSS v.

15.0) (Ganihar 1997, Sample et al. 1993). Ganihar (1997) calculated beta coefficients for

each arthropod Order; I used these coefficients as well as the recommended model to

predict total biomass per sample (by stand and month). I calculated relative biomass

index by dividing the total biomass by dry leaf weight.

To create a relative bird abundance index, I divided the number of detections by the

transect length for each stand. Stands differed in size and shape and transect lengths

differed among stands as well. I used the greatest number of individuals detected among

the three surveys to estimate the relative abundance of each species. I grouped species

into four guilds based on their migration patterns (Sauer et al. 1996, Imhof 1976), nesting

location (Ehrlich et al. 1986), foraging location (Ehrlich et al. 1986), and habitat

51

Table 3.1. Guild memberships of all songbird species detected on eighteen upland pine-hardwood plots one year after forest treatment

in Bankhead National Forest, AL, classified by: forage guild (A, aerial; F, foliage; G, ground; N, nectar; B, bark) (Ehrlich et al. 1986),

nest location (G, ground; S, shrub; T, tree; C, cavity) (Ehrlich et al. 1986), migratory destination (N, Neotropical migrant; T, temperate

migrant; R, resident) (Sauer et al. 1996, Imhof 1976), and habitat association (O/E, open-edge; I/E, interior-edge; I, interior) (Blake

and Karr 1987, Freemark and Collins 1992).

Species

Code

Common Name Scientific Name Forage

Guild

Nest

Guild

Migration

Guild

Habitat

Guild ACFL Acadian Flycatcher Empidonax virescens Vieillot A T N I

BAWW Black-and-White Warbler Mniotilta varia Linnaeus B G T I

BGGN Blue-gray Gnatcatcher Polioptila caerulea Linnaeus F T T I/E

BHCB Brown-headed Cowbird Molothrus ater Boddaert G P R O/E

BHNU Brown-headed Nuthatch Sitta pusilla Latham B C R I

BHVI Blue-headed Vireo Vireo solitarius Wilson F T N I/E

BLJA Blue Jay Cyanocitta cristata Linnaeus F T R I/E

BRTH Brown Thrasher Toxostoma rufum Linnaeus G S T O/E

BTGW Black-throated Green Warbler Dendroica virens Gmelin F T N I

CACH Carolina Chickadee Poecile carolinensis Audubon F C R I/E

CARW Carolina Wren Tryothorus ludovicianus Latham G C R O/E

DOWO Downy Woodpecker Picoides pubescens Linnaeus B C R I/E

EAPH Eastern Phoebe Sayornis phoebe Latham C C R I/E

EATO Eastern Towhee Pipilo erythrophthalmus Linnaeus G G N I/E

EAWP Eastern Wood-pewee Contopus virens Linnaeus A T R I/E

ETTI Eastern Tufted Titmouse Baeolophus bicolor Linnaeus F C N I/E

GCFL Great Crested Flycatcher Myiarchus crinitus Linnaeus A C R I/E

HAWO Hairy Woodpecker Picoides villosus Linnaeus B C N I

HOWA Hooded Warbler Wilsonia citrina Boddaert F S N I

INBU Indigo Bunting Passerina cyanea Linnaeus F S N O/E

KEWA Kentucky Warbler Oporornis formosus Wilson G G NR I/E

LOWA Louisiana Waterthrush Seiurus motacilla Vieillot G G R I/E

51

52

Species

Code

Common Name Scientific Name Forage

Guild

Nest

Guild

Migration

Guild

Habitat

Guild MODO Mourning Dove Lenaida macroura Linnaeus G T N O/E

NOCA Northern Cardinal Cardinalis cardinalis Linnaeus G S R I/E

NOPA Northern Parula Parula Americana Linnaeus F T N I/E

OVEN Ovenbird Seiurus aurocapillus Linnaeus F G R I

PIWA Pine Warbler Dendroica pinus Wilson B T R I/E

PIWO Pileated Woodpecker Dryocopus pileatus Linnaeus B C T I

PRWA Prairie Warbler Dendroica discolor Vieillot F S N O/E

REVI Red-eyed Vireo Vireo olivaceus Linnaeus F S N I/E

RTHU Ruby-throated Hummingbird Archilochus coulbris Linnaeus N T N O/E

SCTA Scarlet Tanager Piranga olivacea Gmelin F T N I

SUTA Summer Tanager Piranga ruba Linnaeus F T R I/E

WBNU White-breasted Nuthatch Sitta carolinensis Latham B C T I

WEVI White-eyed Vireo Vireo griseus Boddaert F S N O/E

WEWA Worm-eating Warbler Helmitheros vermivorus Gmelin F G N I

WOTH Wood Thrush Hylocichla mustelina Gmelin G T N I/E

YBCH Yellow-breasted Chat Icteria virens Linnaeus F S N O/E

YBCU Yellow-billed Cuckoo Coccyzus americanus Linnaeus F T N I/E

YTVI Yellow-throated Vireo Vireo flavifrons Vieillot F T N I/E

49 5

2

53

association (Blake and Karr 1987, Freemark and Collins 1992) (Table 3.1). To evaluate

similarity among the stands and across years, I calculated Morisita’s similarity index

(Magurran 1988). Morisita’s index is recommended as the best overall measure of

similarity for ecological use (Magurran 1988). The index ranges from 0 to 1, with 0

representing pairs of sites with no species in common and values of 1 representing

complete overlap in sites. I used the Shannon-Weiner diversity index, evenness, and

species richness to describe the community in each stand (Krebs 1998). To standardize

species richness because transect lengths differed among plots, I used rarefaction (Krebs

1998). I inspected all variables for normality visually and statistically using Shapiro-

Wilks tests and all variables met assumptions.

I used two-way analysis of variance (ANOVA) with thin, burn, and block as

factors to test for differences among treatments in the post-treatment bird community,

microclimate, microhabitat, and arthropod availability. I also calculated the differences

between pre- and post-treatment for bird community, microclimate principle components,

and microhabitat principle components and tested these differences using a two-way

ANOVA with thin, burn, and block as main factors. Tukey’s multiple comparisons test

was preformed based on the results of the ANOVA. All analyses were performed in

SPSS (v.15.0) using an alpha level of 0.05.

To investigate variation in abundance of species and guilds as they relate to

microhabitat measures and arthropod availability, I used canonical correspondence

analysis (CCA, CANOCO v. 4.5). I eliminated variables with high correlation (Pearson

correlation > 0.7) to avoid redundancy and over-fitting the model and used only species

that had greater than five detections in the analysis. CCA is a direct gradient analysis

54

technique that compares community composition directly to environmental variables

across a gradient (Palmer 1993). This procedure is a type of ordination, and therefore not

a hypothesis testing technique. CCA is appropriate to use when there are no differences

among stands because it evaluates gradients on a different scale; it examines the trends

and variability within stands.

Results

Microclimate. There were no interactions between burning and thinning for

microclimate one year after treatment (Table 3.2) or for changes following treatment

(Table 3.3). Daytime May relative humidity differed among the treatments (Table 3.4).

Daytime May humidity was higher on burned stands than on burned/thinned stands. The

change in daytime May and June temperature following the treatment was significant

(Table 3.4). The change in daytime temperature was greater on thinned/burned stands

than burned stands in both May and June.

The original eight microhabitat difference variables showed low multivariate

correlation (Kaiser-Meyer-Olkin [KMO] Measure of Sampling Adequacy = 0.423) so I

removed the variable with the lowest multivariate correlation (nighttime May relative

humidity) from the principle component analysis to increase the KMO measure of

sampling adequacy to 0.55. The remaining seven variables were condensed to 2 principle

components (PCs), the first representing daytime climate and the second representing

nighttime climate (Table 3.6). All components with eigen values greater than 1 were

retained. The 2 components retained approximately 84% of the original variation

55

Table 3.2. Results of two-way analysis of variance (ANOVA) on microclimate,

microhabitat, and bird community variables one year after silvicultural treatments in

Bankhead National Forest, 2006-2007.

Burn Thin Thin*Burn

Variable F P F P F P

Microclimate

Daytime May Temp 0.03 0.86 7.61 0.02 2.52 0.14

Daytime June Temp 0.02 0.88 9.36 0.01 0.75 0.40

Daytime May RH 0.34 0.57 7.26 0.02 3.48 0.09

Daytime June RH 0.18 0.68 6.10 0.03 1.22 0.29

Nighttime May Temp 0.10 0.76 0.34 0.57 0.08 0.79

Nighttime June Temp 0.12 0.73 1.09 0.32 0.88 0.37

Nighttime May RH 0.24 0.63 1.56 0.24 0.04 0.84

Nighttime June RH 0.12 0.73 1.53 0.24 0.37 0.56

Microhabitat

Herbaceous ground cover 0.10 0.75 3.86 0.07 0.17 0.68

Woody ground cover 0.01 0.92 11.57 0.01 0.50 0.49

Litter ground cover 8.75 0.01 8.81 0.01 0.09 0.77

Bare ground cover 12.32 0.00 1.63 0.23 3.50 0.09

Litter depth 14.73 0.00 4.14 0.06 8.17 0.01

Canopy cover 0.25 0.63 24.66 0.00 0.17 0.69

Forest level 1 0.34 0.57 1.55 0.24 1.17 0.30

Forest level 2 0.65 0.44 30.94 0.00 0.90 0.36

Forest level 3 7.16 0.02 34.21 0.00 9.79 0.01

Forest level 4 5.35 0.04 11.62 0.01 6.22 0.03

Total basal area 0.01 0.92 20.51 0.00 0.09 0.77

Hardwood basal area 0.15 0.71 11.49 0.01 0.15 0.71

Pine basal area 0.00 0.99 12.72 0.00 1.14 0.31

Snag basal area 3.42 0.09 8.79 0.01 2.15 0.17

Bird Community

Species richness 1.25 0.29 3.51 0.09 0.25 0.63

Relative abundance 1.25 0.29 3.51 0.09 0.25 0.63

Shannon-Weiner Diversity

index 0.10 0.75 3.14 0.10 6.67 0.02

Evenness 0.55 0.47 2.01 0.18 0.06 0.80

Tree nesting abundance 1.62 0.23 11.12 0.01 0.49 0.50

Shrub nesting abundance 0.71 0.42 3.70 0.08 0.08 0.78

Cavity nesting abundance 0.76 0.40 2.33 0.15 1.93 0.19

Ground nesting abundance 0.46 0.51 2.34 0.15 0.05 0.83

Parasite nesting abundance 1.41 0.26 9.95 0.01 1.41 0.26

Bark foraging abundance 0.00 0.98 4.11 0.07 0.45 0.52

Aerial foraging abundance 1.99 0.18 0.87 0.37 0.44 0.52

Ground foraging abundance 1.99 0.18 0.87 0.37 0.44 0.52

Foliage foraging abundance 0.32 0.58 4.93 0.05 0.45 0.52

Neotropical migrant 0.41 0.53 1.32 0.27 0.52 0.48

56

Burn Thin Thin*Burn


abundance

Temperate migrant abundance 0.03 0.87 2.82 0.12 1.89 0.19

Resident abundance 0.01 0.93 8.76 0.01 0.65 0.44

Interior species abundance 0.89 0.36 0.49 0.50 0.00 0.95

Interior/edge species

abundance 0.03 0.86 4.56 0.05 1.57 0.23

Edge/open species abundance 0.14 0.71 39.31 0.00 2.28 0.16

57

Table 3.3. Results of two-way analysis of variance (ANOVA) on differences in

microclimate, microhabitat, and bird community variables before and after silvicultural

treatments in Bankhead National Forest, 2005-2007.

Burn Thin Thin*Burn


Microclimate

Daytime May Temp 0.06 0.81 8.14 0.01 3.41 0.09

Daytime June Temp 0.07 0.79 8.04 0.02 0.84 0.38

Daytime May RH 0.29 0.60 3.82 0.07 2.89 0.12

Daytime June RH 0.18 0.68 4.76 0.05 0.70 0.42

Nighttime May Temp 0.05 0.83 0.19 0.67 0.34 0.57

Nighttime June Temp 0.46 0.51 1.37 0.26 0.72 0.41

Nighttime May RH 0.01 0.91 1.44 0.25 0.07 0.80

Nighttime June RH 0.01 0.91 1.40 0.26 1.16 0.30

Microhabitat

Herbaceous ground cover 0.43 0.53 0.02 0.90 0.65 0.44

Woody ground cover 0.04 0.84 0.66 0.43 0.06 0.81

Litter ground cover 5.36 0.04 4.33 0.06 1.78 0.21

Bare ground cover 10.46 0.01 6.79 0.02 0.34 0.57

Litter depth 6.27 0.03 4.73 0.05 1.14 0.31

Canopy cover 0.13 0.72 15.88 0.00 0.04 0.84

Forest level 1 0.87 0.37 0.64 0.44 0.87 0.37

Forest level 2 0.57 0.46 23.98 0.00 0.04 0.85

Forest level 3 0.01 0.94 28.95 0.00 5.76 0.03

Forest level 4 1.30 0.28 12.83 0.00 0.66 0.43

Bird Community

Species richness 0.00 0.99 0.33 0.58 0.95 0.35

Relative abundance 0.00 0.99 0.33 0.58 0.95 0.35

Shannon-Weiner Diversity

index 0.02 0.89 0.03 0.88 5.66 0.03

Evenness 0.22 0.65 1.13 0.31 1.91 0.19

Tree nesting abundance 7.78 0.02 4.17 0.06 1.18 0.30

Shrub nesting abundance 2.70 0.13 0.44 0.52 0.00 0.97

Cavity nesting abundance 0.00 0.97 1.09 0.32 26.37 0.00

Ground nesting abundance 0.01 0.91 2.32 0.15 0.01 0.94

Parasite nesting abundance 0.05 0.83 1.69 0.22 0.05 0.83

Bark foraging abundance 0.00 0.95 0.73 0.41 0.61 0.45

Aerial foraging abundance 0.48 0.50 0.97 0.34 0.63 0.44

Ground foraging abundance 0.96 0.35 0.32 0.58 0.33 0.58

Foliage foraging abundance 2.67 0.13 0.34 0.57 7.12 0.02

Neotropical migrant

abundance 2.43 0.14 1.01 0.34 0.00 0.98

Temperate migrant abundance 0.10 0.76 3.56 0.08 4.00 0.07

Resident abundance 1.37 0.27 1.38 0.26 5.69 0.03

Interior species abundance 0.03 0.86 2.43 0.14 0.25 0.63

58

Burn Thin Thin*Burn


Interior/edge species

abundance 7.75 0.02 0.16 0.70 2.05 0.18

Edge/open species abundance 0.24 0.64 9.88 0.01 1.75 0.21

59

Table 3.4 Results of one-way analysis of variance (ANOVA) for microclimate variables among four silvicultural treatments in

Bankhead National Forest, AL, one year after treatment, 2006-2007. Means within a row with different superscript numbers differ

(Tukey P<0.05).

ANOVA Mean ± SE by treatment

Climate Variable P F df Control Burn Thin Thin/Burn

Daytime

May Temperature 0.053 3.423 3 23.09±0.98 21.25±0.81 24.31±1.02 25.78±0.63

June Temperature 0.052 3.444 3 24.85±1.35 23.94±0.52 27.65±0.80 28.94±1.28

May Relative Humidity 0.047 3.58 3 52.61±8.72ab

60.37±4.93b 49.99±1.54

ab 45.93±1.80

a

June Relative Humidity 0.115 2.442 3 59.82±6.25 64.77±1.51 5.41±1.92 53.23±2.51

Nighttime

May Temperature 0.894 0.201 3 18.82±1.19 18.79±0.32 19.60±0.90 19.06±0.74


May Relative Humidity 0.626 0.602 3 63.44±7.35 66.58±7.05 58.77±4.73 60.05±1.43

June Relative Humidity 0.545 0.746 3 71.87±4.18 70.89±4.94 64.67±3.73 68.42±2.26

59

60

Table 3.5 Results of one-way analysis of variance (ANOVA) of changes in microclimate variables following four silvicultural

treatments in Bankhead National Forest, AL, 2006-2007. Means within a row with different superscript numbers differ

(Tukey P < 0.05).


Variable P F df Control Burn Thin Thin/Burn

Daytime

May Temperature 0.04 3.90 3 2.66±1.07ab

0.72±1.07a 3.59±0.76

ab 5.08±0.76

b


May Relative Humidity 0.14 2.23 3 -12.82±7.64 -5.27±6.89 -15.64±1.42 -18.29±1.96

June Relative Humidity 0.20 1.83 3 -16.59±3.58 -12.70±3.58 20.77±2.53 -22.06±2.53

Nighttime

May Temperature 0.91 0.18 3 0.61±1.06 1.36±1.06 1.54±0.75 1.21±0.75

June Temperature 0.54 0.76 3 -0.50±0.62 0.45±0.75 1.37±1.10 0.46±0.27

May Relative Humidity 0.68 0.52 3 -8.10±4.87 -8.70±4.87 -14.27±3.44 -12.66±3.44

June Relative Humidity 0.45 0.94 3 -11.36±4.19 -17.82±4.19 -19.56±2.96 -15.22±2.96

Principle Components

PC 1 (daytime climate) 0.05 3.47 3 0.43±0.47 1.13±0.47 -0.16±0.33 -0.62±0.33

PC 2 (nighttime climate) 0.55 0.74 3 0.71±0.63 0.23±0.63 -0.38±0.44 -0.09±0.44

60

61

Table 3.6. Principle component analysis loadings, eigenvalues, and percent variance for

the change in microclimate variables following silvicultural treatment in Bankheand

National Forest, AL, 2005-2007.

PC1 PC2

Day May Temp -0.874 -0.241

Day June Temp -0.637 -0.608

Day June Relative Humdity 0.889 0.406

Night May Temperature 0.737 -0.267

Night May Relative Humdity -0.380 0.779

Night June Relative Humdity -0.522 0.807

Night June Temperature 0.556 -0.753

Day May Relative Humidity 0.715 0.523

Eigenvalue 3.741 46.770

% Variance 2.76 34.55

60

62

(Bartlett’s Test of Sphericity χ2 = 117.765, df = 21, p = 0.000). Neither microclimate PC

was significantly different among treatments (Table 3.5).

Microhabitat. There was an interaction between burning and thinning for litter

depth and presence of forest level three and four one year after treatment (Table 3.2).

Thinning reduces the amount of litter depth and the presence of forest levels three and

four regardless of whether they were burned or not (Fig 3.3, 3.4, 3.5). However, when

burning is not combined with thinning, it results in a less litter depth and lower presence

of forest levels three and four (Fig 3.3, 3.4, 3.5). There was an interaction between

burning and thinning in the change in forest level three presence following treatment

(Table 3.3). Burning resulted in a decreased presence of forest level three when

combined with thinning, but when only burning was performed, the presence of forest

level three increased (Fig. 3.6). One year after treatment, all microhabitat variables

except percent herbaceous cover and presence of forest level one differed among the

treatments (Table 3.7). Thinned and thinned/burned stands had higher percentage of

woody ground cover (17% and 19%, respectively) than the untreated or burned stands

(7% and 9% respectively). Litter cover was highest on untreated stands (99%), whereas

bare ground was highest on thinned/burned stands (6%). As expected, canopy cover and

BA were lowest on stands that had been thinned (63% and 67 ft2/acre). The BA of pines

and snags was higher on the control (119 ft2/acre and 9 ft

2/acre, respectively) than on the

thinned stands (97 ft2/acre and 4 ft

2/acre, respectively). Presence of forest level two was

greatest on the control and the burn. Burned stands had the greatest presence of forest

level three (22 %).

63

Figure 3.3. Litter depth interaction between burning

and thinning in the Bankhead National Forest, AL,

2006-2007.

Figure 3.4. Presence of forest level 3 interaction between

burning and thinning in the Bankhead National Forest, AL,

2006-2007.

64

Figure 3.5. Interaction between burning and thinning of

presence of forest level 4 in the Bankhead National Forest,

AL, 2006-2007.

Figure 3.6. Interaction between burning and thinning in the

change in presence of forest level 3 following silvicultural

treatment in the Bankhead National Forest, AL, 2006-2007.

65

Table 3.7 Results of one-way analysis of variance (ANOVA) of habitat variables among four silvicultural treatments in Bankhead

National Forest, AL, one year after treatment, 2006-2007. Means within a row with different superscript numbers differ (Tukey P <

0.05).


Habitat Variable P F df Control Burn Thin Thin/Burn

Ground cover: % herbaceous plants 0.30 1.36 3 11.25±4.83 14.58±5.02 22.01±3.93 21.58±2.83

Ground cover: % woody plants 0.03 4.07 3 6.81±1.14 8.61±3.62 19.10±3.14 16.67±2.63

Ground cover: % litter 0.01 6.04 3 99.44±0.28a 97.5±1.05

ab 97.92±0.55

ab 91.81±2.06

b

Ground cover: % bare ground 0.00 8.12 3 0a 1.53±0.77

ab 0.76±0.25

a 6.11±1.62

b

Litter depth (cm) 0.01 7.23 3 7.7±0.3b 3.7±0.8

a 4.8±0.3

a 4.2±0.8

a

Canopy cover 0.00 8.43 3 91.03±1.01b 90.44±2.22

b 63.29±1.63

a 60.39±6.88

a

Forest level 1 present 0.46 0.92 3 11.33±3.38 8.00±1.15 11.67±1.63 12.67±1.33

Forest level 2 present 0.00 11.08 3 22.00±1.53b 23.00±2.65

b 7.33±0.95

a 5.67±1.73

a

Forest level 3 present 0.00 15.66 3 11.67±1.20a 22.33±2.19

b 6.67±0.92

a 5.83±2.01

a

Forest level 4 present 0.01 6.77 3 25.67±1.33a 20.33±4.26

b 18.83±2.71

b 19.33±2.76

b

Basal Area: Total (ft2/acre) 0.01 6.81 3 162.22±12.81

b 156.67±13.88

b 66.67±7.79

a 77.78±19.71

a

Basal Area: Hardwoods (ft2/acre) 0.04 3.98 3 44.44±24.44 44.44±25.02 25.00±3.15 20.00±17.33

Basal Area: Pines (ft2/acre) 0.02 4.67 3 118.89±11.28

b 96.67±4.84

ab 39.44±5.76

a 57.78±3.44

ab

Basal Area: Snags (ft2/acre) 0.03 4.34 3 8.89±1.11

b 4.44±2.94

ab 3.33±2.11

a 2.22±1.11

a

65

66

Table 3.8 Results of analysis of variance (ANOVA) of changes in microhabitat variables following four silvicultural treatments in

Bankhead National Forest, AL, 2006-2007. Means within a row with different superscript numbers differ (Tukey P<0.05).


Variable P F df Control Burn Thin Thin/Burn

Ground cover: % herbaceous plants 0.66 0.54 3 1.94±6.25 1.11±6.25 -1.74±4.42 6.16±4.42

Ground cover: % woody plants 0.84 0.84 3 1.67±4.00 1.53±4.00 3.61±2.82 5.21±2.82

Ground cover: % litter 0.01 0.19 3 0.42±0.64b -1.95±1.01

ab -1.39±0.65

ab -7.78±1.92

a

Ground cover: % bare ground 0.02 6.79 3 0a 1.53±0.77

ab 0.76±0.25

ab 6.11±1.62

b

Litter depth 0.04 0.04 3 3.01±0.85b 0.37±0.85

ab 0.62±0.60

ab -0.44±0.60

a

Canopy cover 0.01 5.38 3 4.79±6.68b 3.88±6.68

ab -17.04±4.72

ab -20.38±4.72

a

Forest level 1 present 0.60 0.65 3 -8.33±2.89 -13.00±2.89 -8.67±2.05 -8.67±2.05

Forest level 2 present 0.00 8.26 3 1.67±3.44c 1.55E-15±3.40

bc -12.33±2.43

ab -15.17±2.43

a

Forest level 3 present 0.00 11.77 3 -2.67±2.33bc

2.33±2.33c -8.67±1.64

ab -13.33±1.54

a

Forest level 4 present 0.02 4.78 3 -1.00±2.36ab

3.00±2.36b -6.67±1.67

a -6.00±1.67

a

PC 1 (Ground cover) 0.00 14.96 3 0.98±0.17b 1.35±0.10

b -0.61+0.20

a -0.56±0.29

a

PC 2 (Understory cover) 0.03 4.24 3 0.77±0.20b -0.16±0.3

ab 0.46±0.11

ab -0.76±0.55

a

PC 3 (Midstory cover) 0.88 0.22 3 -0.21±0.21 -0.24±0.08 -0.03±0.39 0.26±0.62

PC 4 (Overstory cover) 0.19 1.84 3 0.35±0.34 0.50±0.68 -0.47±0.37 0.05±0.48

66

67

The change in percent litter cover, percent bare ground, litter depth, canopy cover,

and presence of forest levels two and four were different across treatments (Table 3.8).

The change in litter ground cover and bare ground cover was greatest on the

thinned/burned stands. Litter depth decreased on the thinned/burned stands and increased

slightly on burned, thinned, and untreated stands. As expected, the change in canopy

cover was greatest on the stands that had been thinned. The presence of forest level two

decreased on all treated stands; the greatest decrease was on thinned and thinned/burned

stands. The presence of forest level four decreased on the untreated, thinned, and

thinned/burned stands, and increased on the burned stands.

I grouped the original thirteen difference variables into 4 principle components (PCs),

the first representing ground cover, the second representing understory cover, the third

representing midstory cover, and the fourth representing overstory cover (Table 3.9). All

components with an eigen value greater than 1 were retained. The 4 components retained

approximately 85% of the original variation (Bartlett’s Test of Sphericity χ2 = 194.022, df

= 78, p = 0.000). PC1 (ground cover) and PC2 (understory cover) differed among the

treatments (Table 3.8). PC1 (ground cover) decreased on the thinned and thinned/burned

stands and it increased on the untreated and burned stands (Table 3.8). The increase in

PC2 understory cover) was greater on control stands than on the thinned/burned stands

(Table 3.8).

Arthropod availability. There were no differences in arthropod biomass index among

treatments (Table 3.10), nor were there any interactions between the treatments (Table

3.2).

68

Table 3.9. Principle component analysis loadings, eigenvalues, and percent variance for

the change in microhabitat variables following silvicultural treatment in Bankhead

National Forest, AL, 2005-2007.

PC1 PC2 PC3 PC4

Herb Cover 0.099 0.795 -0.062 0.383

Woody Cover 0.003 0.925 0.073 -0.192

Litter depth 0.702 0.013 -0.408 0.504

Canopy Cover 0.561 -0.557 0.371 0.141

Forest Level 1 0.198 0.616 -0.446 0.401

Forest Level 2 0.361 -0.461 0.604 0.233

Forest Level 3 0.233 0.020 0.916 0.163

Forest Level 4 0.060 0.044 0.296 0.914

Bare Cover -0.939 0.025 -0.195 -0.111

Litter Cover 0.911 0.172 0.262 -0.072

Eigenvalue 3.56 2.70 1.26 1.13

% Variance 35.58 29.96 12.57 11.29

69

Table 3.10. Results of one-way analysis of variance (ANOVA) of arthropod biomass index among four silvicultural treatments in

Bankhead National Forest, AL, one year after treatment, 2006-2007.


Arthropod Variable P F df Control Burn Thin Thin/Burn

April Biomass (g/10g dry leaves) 0.435 0.978 3 49.98±10.93 35.29±6.23 58.61±15.77 120.21±53.85

May Biomass (g/10g dry leaves) 0.069 3.061 3 133.99±29.23 44.94±22.48 60.23±25.18 41.90±9.38

June Biomass (g/10g dry leaves) 0.163 2.031 3 126.69±61.84 33.97±14.69 68.17±22.06 54.76±25.22

69

70

Bird community. A total of 983 birds were detected one year after treatment,

representing 40 species (Table3.1). The most abundant species were the red-eyed vireo

(Vireo olivaceus Linnaeus), comprising 16.5% (162 detections) of total individuals, and

the pine warbler (Dendroica pinus Wilson), comprising 14.0% (138 detections) of total

individuals. Species detected post treatment that were not detected before treatment were

the brown-headed nuthatch (Sitta pusilla Latham), eastern phoebe (Sayornis phoebe

Latham), eastern towhee (Pipilo erythrophthalmus Linnaeus), eastern wood-pewee

(Contopus virens Linnaeus), mourning dove (Zenaida macroura Linnaeus), ruby-throated

hummingbird (Archilochus coulbris Linnaeus), and yellow-throated vireo (Vireo

flavifrons Vieillot). Two species (blue grosbeak [Guiraca caerulea Linnaeus] and red-

bellied woodpecker [Melanerpes carolinus Linnaeus]) detected before treatments were

not detected post-treatment.

There was an interaction in Shannon-Weiner diversity index between burning and

thinning one year after treatment (Table 3.2). When combined with thinning, burning

results in lower diversity, but burning alone results in higher bird diversity (Fig. 3.7).

There was an interaction between the two treatments in changes in Shannon-Weiner

diversity index, cavity nesting species abundance, foliage foraging species abundance,

and resident species abundance following the treatment (Table 3.3). For all four

variables, when thinning is combined with burning the result is a smaller change in the

variable (Fig. 3.8, 3.9, 3.10, 3.11). However, when burning is done alone, there is a

larger change in the variable.

Parasite nesting species abundance (i.e. brown-headed cowbirds), and edge/open

habitat species abundance differed among the treatments (Table 3.11). Parasite nesting

71


Shannon-Weiner Diversity Index following silvicultural treatment

in the Bankhead National Forest, AL, 2006-2007.


change in Shannon-Weiner Diversity Index following

silvicultural treatment in the Bankhead National Forest, AL,

2006-2007.

72


change in cavity nesting bird abundance following silvicultural



change in foliage foraging bird abundance following silvicultural


73

Figure 3.11. Interaction between burning and thinning in

the change in resident bird abundance following

silvicultural treatment in the Bankhead National Forest,

AL, 2006-2007.

74

Table 3.11. Results of analysis of variance (ANOVA) of bird community variables among silvicultural treatments in Bankhead

National Forest, AL, one year after treatment, 2006-2007. Means within a row with different superscript letters differ (Tukey p<0.05).


Community Variable p F df Control Burn Thin Thin/Burn

Species richness 0.24 1.59 3 9.99±0.22 10.82±0.51 11.21±0.23 11.53±0.57

Relative abund (detections per

100m) 0.24 1.59 3 79.89±1.77 86.58±4.10 89.71±1.84 92.28±4.52

Shannon-Weiner diversity index 0.05 3.38 3 2.36±0.10a 2.6±0.04

ab 2.72±0.08

b 2.53±0.07

ab

Evenness 0.85 0.49 3 0.90±0.01 0.91±0.02 0.93±0.01 0.93±0.02

Nesting Guild Abundance

Tree 0.03 4.28 3 7.62±0.98ab

5.24±0.59a 12.85±1.68

b 12.44±2.71

ab

Shrub 0.24 1.60 3 9.05±0.84 8.32±1.43 15.85±4.11 13.69±4.25

Cavity 0.27 1.48 3 4.80±1.55 8.71±1.36 9.86±1.44 8.96±1.60

Ground 0.42 1.01 3 5.09±1.49 4.53±1.78 3.50±1.05 2.42±0.84

Parasite 0.02 4.73 3 0 a 0

a 0.62±0.30

ab 1.37±0.44

b

Foraging Guild Abundance

Bark 0.26 1.54 3 3.86±1.10 5.02±1.05 8.41±0.51 7.32±2.40

Aerial 0.28 1.43 3 1.63±1.00 2.04±0.59 1.78±0.38 2.91±0.42

Ground 0.28 1.43 3 13.02±8.03 16.29±4.74 14.20±3.02 23.27±3.39

Foliage 0.16 2.02 3 16.12±1.48 17.10±4.02 25.96±3.18 23.17±5.38

Migratory Guild Abundance

Neotropical 0.58 0.67 3 17.27±2.62 13.99±1.25 19.02±2.98 20.52±5.14

Temperate 0.22 1.71 3 1.17±0.58 3.07±1.58 5.10±1.65 2.97±1.00

Resident 0.06 3.18 3 7.82±0.47 9.76±1.85 18.04±0.89 15.61±3.50

Habitat Guild Abundance

Interior 0.70 0.49 3 10.06±2.37 8.24±2.58 8.68±1.32 7.10±1.29

Interior/edge 0.14 2.18 3 14.85±0.76 17.22±1.77 22.29±1.71 19.15±2.56

Edge/open 0.00 14.16 3 1.64±0.50a 3.00±1.81

a 12.28±2.84

b 8.55±4.85

b

74

75

species abundance was highest on thinned and thinned/burned stands, and edge/open

habitat species abundance was higher on thinned and thinned/burned stands than

untreated or burned stands.

Following silviculture treatment, the change in abundance of tree and cavity nesting

species, interior/edge species, and edge/open species differed among the treatments

(Table 3.12). The greatest decrease in tree nesting species was on burned stands, whereas

there was an increase on thinned stands. Cavity nesting species increased on burned and

thinned stands and decreased on untreated and thinned/burned stands. Foliage foraging

species decreased on all stands, but the greatest change was on thinned/burned stands.

Interior edge species decreased on all stands; the biggest decrease was on burned and

thinned/burned stands. Edge/open species increased the most on thinned and

thinned/burned stands.

The post treatment bird community included fifteen species listed in Partners in

Flight’s (PIF) North American Landbird Conservation Plan as Species of Continental

Importance (Rich et al. 2004, Table 3.13). Three new species of concern were detected

after treatment (Table 3.13). PIF lists species in two categories; WatchList species are

species that have multiple reasons (restricted distribution, low population size,

widespread population declines, high threats to habitat, etc.) for conservation concern

across their entire range (Rich et al. 2004). Stewardship species are species which have a

high percentage of their global population within a single North American biome (Rich et

al. 2004).

Morisita’s similarity indices indicate that species composition on the untreated stands

is most similar to the burned stands and least similar to the thinned stands (Table 3.14).

76

Table 3.12. Results of one-way analysis of variance (ANOVA) of changes in bird community variables following four silvicultural

treatments in Bankhead National Forest, AL, 2006-2007. Means within a row with different superscript numbers differ (Tukey

P<0.05).

ANOVA Mean ±SE by treatment

Variable p F df Control Burn Thin Thin/Burn

Species richness 0.71 0.47 3 2.46±1.08 -1.45±1.08 -2.08±0.76 -3.01±0.76

Relative abundance 0.71 0.47 3 -19.68±8.64 -12.50±8.64 -16.7±6.11 -24.07±6.11

Shannon-Weiner diversity 0.16 2.05 3 -0.11±0.15 0.21±0.15 0.17±0.10 -0.11±0.10

Evenness 0.42 1.01 3 0.00±0.03 0.04±0.03 0.01±0.02 -0.01±0.02

Nesting Guild Abundance

Tree 0.01 5.51 3 -3.68±1.99ab

-6.61±1.99a 1.72±1.41

b -4.97±1.41

ab

Shrub 0.37 1.14 3 -1.60±2.61 -5.40±2.61 -0.02±1.85 -3.83±1.85

Cavity 0.00 10.3 3 -2.05±1.30ab

3.67±1.30c 2.54±0.9

bc -3.26±0.92

a

Ground 0.53 0.78 3 -0.82±2.53 -0.73±2.53 -4.32±1.79 -3.89±1.79

Parasite 0.62 0.61 3 0 0 0.47±0.21 0.67±0.68

Foraging Guild Abundance

Bark 0.70 0.49 3 -2.95±2.25 -1.55±2.25 0.24±1.59 -1.40±1.59

Aerial 0.48 0.86 3 -0.19±0.79 -0.12±0.79 1.03±0.56 0.01±0.56

Ground 0.55 0.73 3 9.09±5.67 11.91±5.67 9.84±4.01 17.49±4.01

Foliage 0.02 4.87 3 -8.23±2.85ab

-5.68±2.85ab

-3.1±2.02b -13.70±2.02

a

Migratory Guild Abundance

Neotropical 0.34 1.24 3 -2.53±3.60 -7.50±3.60 -5.76±2.56 -10.56±2.56

Temperate 0.10 2.57 3 -2.78±1.38 -0.03±1.38 1.85±0.97 -0.16±0.97

Resident 0.04 3.80 3 -4.23±2.55 -1.55±2.55 3.63±1.80 -4.22±1.80

Habitat Guild Abundance

Interior 0.45 0.94 3 -2.27±4.46 -1.05±4.46 -6.35±3.15 -8.99±3.15

Interior/edge 0.02 4.72 3 -2.89±3.12ab

-6.58±3.12ab

-0.1±2.23b -11.57±2.23

a

Edge/open 0.03 4.20 3 -1.19±2.33a 0.49±2.33

ab 7.81±1.65

b 4.16±1.65

ab

76

77

Table 3.13. Species of Continental Importance, as listed by the Partners in

Flight Landbird Conservation Plan (Rich et al. 2004), detected on upland

pine-hardwood plots before and after silvicultural treatments in Bankhead

National Forest, AL, 2005-2007. See table 2.1 for scientific names.

PIF Pre-treatment Post-treatment

Species Listing* Individuals Plots Individuals Plots

Acadian Flycatcher S 7 8 5 5

Brown-headed Nuthatch W 0 0 1 1

Brown Thrasher S 1 1 1 1

Carolina Wren S 15 11 21 9

Eastern Towhee S 0 0 1 1

Hooded Warbler S 52 13 20 12

Indigo Bunting S 38 16 47 14

Kentucky Warbler W 6 6 12 8

Louisiana Waterthrush S 1 1 2 2

Pine Warbler S 80 18 68 18

Prairie Warbler W 5 5 28 10

White-eyed Vireo S 5 4 4 4

Worm-eating Warbler W 53 15 28 16

Wood Thrush W 2 1 4 4

Yellow-throated Vireo S 0 0 2 2

*S = Stewardship Species; W = WatchList Species (Rich et al. 2004)

78

Table 3.14. Morisita’s similarity index for the breeding

bird community one year after silvicultural treatment in

Bankhead National Forest, AL, 2006-2007.

Control Burn Thin Thin/Burn

Control - 0.99 0.74 0.91

Burn 0.99 - 0.85 0.91

Thin 0.74 0.85 - 1.01

Thin/Burn 0.91 0.91 1.01 -

Table 3.15. Morisita’s similarity index for the breeding bird

community before and one year after silvicultural treatment in


Post treatment

Control Burn Thin Thin/Burn

Pre

trea

tmen

t Control 1.01 1 0.89 0.95

Burn 0.94 0.9 0.84 0.89

Thin 0.98 0.94 0.94 0.97

Thin/Burn 0.99 0.99 0.92 1.02

79

Species composition was similar before and after treatment on all stands, with a small

change on the burned and thinned stands (Table 3.15).

Canonical correspondence analysis. The CCA of microhabitat characteristics,

arthropod availability, and species abundance explained 48.8 % (total inertia = 0.847) of

the variation in the first three axes. Axis one explained 21.1% of the variation

(Eigenvalue = 0.178), the second axis 15.3% (Eigenvalue = 0.130), and the third axis

12.4% (Eigenvalue = 0.104). Based on the CCA of microhabitat characteristics,

arthropod availability, and nesting guild abundance, the first three axes explained 74.9%

(total inertia = 0.119) of the variation in guild abundance. The first axis explained 39.9%

(Eigenvalue = 0.048) of the variation, the second 21.9% (Eigenvalue = 0.026), and the

third 13.1% (Eigenvalue = 0.016). The CCA of the microhabitat characteristics,

arthropod availability and foraging guild abundance explained 90.9% (total inertia =

0.069) of the variation in the first three axes. Axis one explained 37.2% (Eigenvalue =

0.026), the second axis 31.5% (Eigenvalue = 0.022), and the third 22.2% (Eigenvalue =

0.015).

The CCA of microhabitat characteristics, arthropod availability, and species

abundance revealed a gradient in microhabitat characteristics apparent in the position of

variables along the axes of the ordination plots (Fig. 3.12). On one end of the gradient is

canopy cover and presence of forest level four, on the other is woody and herbaceous

ground cover and presence of forest level one. Another gradient from tree species

richness, basal area, and presence of forest level three to a blank area on the ordination

indicates that open areas were not represented by any of the habitat variables collected.

Open habitat species (yellow-breasted chat [Icteria vierns Linnaeus], eastern wood-

80

pewee, and morning dove) and generalist species (eastern tufted titmouse [Baeolophous

bicolor Linnaeus], Carolina chickadee [Poecile carolinensis Audubon], and summer

tanager [Piranga rubra Linnaeus]) are found in this area of the ordination plot (Figure

3.12). Early successional species (Kentucky warbler [Oporornis formosus Wilson],

indigo bunting [Passerina cyanea Linnaeus], and prairie warbler[Dendroica discolor

Vieillot]) were associated with herbaceous and woody ground cover and presence of

forest level one, whereas more interior species (worm-eating warbler [Helmitheros

vermivorus Gmelin], acadian flycatcher [Empidonax virescens Vieillot], and black-

throated green warbler [Dendroica virens Gmelin]) were on the other end of the gradient,

associated with the presence of forest level three, basal area, basal area of hardwoods and

snags, and litter depth (Fig. 3.12)

A similar gradient was revealed in the CCA of habitat characteristics, arthropod

availability and nesting guild associations. The ordination plot revealed a gradient from

basal area and presence of forest level four to herbaceous and woody ground cover and

presence of forest level one, and also a gradient from canopy cover and presence of forest

level three to litter depth, litter ground cover, and tree species richness (Fig. 3.13).

Parasite nesting guild was on the edge of the plot, indicating that there were no strong

associations with the environmental variables. Ground nesting species were associated

with high litter ground cover; cavity nesting species were associated with basal

area of snags and presence of forest level four; and tree nesting species were associated

with presence of forest level three and canopy cover (Fig. 3.13).

The CCA of microhabitat characteristics, arthropod availability, and foraging guild

associations revealed a gradient that was different from the first two analyses. On

81

Figure 3.12. First and second canonical correspondence axes for microhabitat

characteristics, arthropod availability, and bird species abundance one year after

silvicultural treatments, Bankhead National Forest, AL, 2006-2007. See table 3.1 for

species codes.

82


characteristics, arthropod availability, and nesting guild abundance one year after

silvicultural treatments, Bankhead National Forest, AL, 2006-2007.

83

one end of the gradient was the presence of forest level one and four, tree species

richness, basal area, and woody and herbaceous ground cover; on the other end was

canopy cover, basal area of snags, litter ground cover, litter depth, and the presence of

species was associated with litter cover, snag BA, and hardwoods BA (Fig 3.13).

forest level three (Fig. 3.14). In the center of the plot was foliage foraging species,

indicating that they are more generalist species, and on the far edges of the plot, opposite

one another, were aerial feeding species, and ground foraging species (Fig. 3.14). Bark

foraging

Discussion

One year after treatment there is a treatment affect on some aspects of the bird

community; it is likely a result of changes in microhabitat among treatments. Thinning

had a greater impact on the bird community than burning, although burning affected the

bird community on a smaller scale. Treated stands had a higher diversity than untreated

stands. This is a common effect of any forest disturbance where a more heterogenic

habitat is created (Roth 1976). Thinning resulted in a decrease in canopy cover, vertical

structure, and the lowest basal area of all stands. However, one year after the treatment

there was much shrubs and herbaceous plant regeneration. As a result of this

regeneration, thinned stands had a high abundance of tree nesting species. This

corroborates other studies that have found that may tree and shrub nesting birds use

regenerating stands shortly after cutting (Gram et al. 2003, Harrison et al. 2005, Heltzel

84


characteristics, arthropod availability, and foraging guild abundance one year after

silvicultural treatments, Bankhead National Forest, AL, 2006-2007.

85

and Leberg 2006, Holmes and Pitt 2007). No difference was found in arthropod biomass

however; leaf samples were taken at every sampling location regardless of tree Arthropod

availability. Since I indexed arthropod abundance by branch clippings that did not reflect

the relative availability of leaves in different treatments (i.e., control and burn only stands

had more trees than thinned and thinned/burned stands), there could be a difference that

was not detected by my methods. Biomass in April appears to have affected the

abundance of foliage foraging species. Canonical correspondence analysis shows a strong

relationship between foliage foraging species and arthropod biomass in April, when they

arrived on the breeding grounds. Thinned stands created habitat for edge/open habitat

species, but still maintained many of the interior species. Many other studies have found

that when some trees are retained, as in shelterwood and selection cuts, edge and open

habitat bird species use the habitat for a short time and many mature forest birds remain

(Campbell et al. 2007, Greenberg et al. 2007, Holmes and Pitt 2007, Lanham et al. 2002,

Vanderwel et al. 2007, Weakland et al. 2002). Silvicultural treatments that leave trees

appear to be viable options for creating habitat for early-successional birds if clear cutting

is not an option or if retaining mature forest birds is also a management goal. However,

Costello et al. (2000) suggested that there may be a minimum opening size requirement

for some species associated with early successional habitat. Treatments that retain some

trees may not create openings large enough to support all species that use early

successional habitat for breeding.

Low intensity burns used in this study resulted in a decrease in the presence of the

shrub layer, a decrease in litter depth, and an increase in bare ground. Diversity increased

86

in the stands, indicating that the increased heterogeneity created by the fire’s patchiness

created more diverse habitat than was available before the treatment. Previous studies

found that patchiness created with low-intensity fire results in diverse habitats which are

attractive to a large variety of birds (Greenberg 2007, Blake 2005, Lanham et al. 2002,

Stribling and Barron 1995).

My results suggest that burning and thinning in combination has a more negative

effect on certain bird groups than either treatment by itself one year after treatment.

Burned/thinned plots had a lower diversity than the other treatments, tree and cavity

nesting guilds decreased and foliage foraging birds decreased, likely a result of a decrease

in foliage in the stands. Edge/open habitat species increased while interior/edge habitat

species decreased. Only one study has looked at the effect of combined burning and

thinning (Wilson et al. 1995), but their results differed from mine. They found higher

densities in stands that had been thinned and burned than stands that had only been

thinned.

Large increase in prairie warblers in thinned stands indicates that treatments are

providing habitat for this species of concern, while the constant number in burned stands

indicates that burning is not detrimental to them. Abundance increased the most (from 1

to 19) on thinned stands, which suggests that thinning may provide their preferred

habitat. Gram et al. (2003) found higher prairie warbler abundance in clearcut stands

when 10-15 percent of the trees were left standing, similar to a seed tree cut. They

preferred this habitat to small group selection cuts, single tree selection cuts, or uncut

stands. It appears that they are attracted to treatments that promote understory growth

and remove a large portion of overstory trees.

87

There is no single management system that will provide habitat for all species of

forest birds. Some species respond positively and other respond negatively to any given

management system. Bird responses are often scale dependent and landscape level

effects are also important. My results suggest that ‘free’ thinning, and to a lesser extent,

low intensity prescribed burning, provides habitat for early successional birds while

retaining many mature forest birds one year after treatment. Regenerating forests provide

only temporary habitat for early successional species, so it would be appropriate to time

rotations and burning so that there is consistent availability of early successional breeding

habitat across the landscape, if that is the goal of the management program.

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CHAPTER 4

HOME RANGE SIZE, HABITAT USE, AND REPRODUCTIVE SUCCESS OF

HOODED WARBLERS AND WORM-EATING WARBLERS IN THINNED AND

BURNED FOREST STANDS

Introduction

Avian community parameters such as abundance and species richness provide

information about how silvicultural treatments affect bird community composition and

structure; however these measurements are not necessarily indications of reproductive

success and fitness (Vickery et al. 1992a). For a more thorough understanding of how

the silvicultural treatments affect the fitness of individual birds, a more detailed

examination of bird behavior and reproduction has been recommended (Thompson et al.

2000). Observations of space use by monitoring and estimating home range and core

area are indirect approaches to examine factors that affect individual fitness. Observing

nesting behavior and estimating nest success provides a more direct measure of

individual bird fitness.

Home range has been defined as “that area traversed by the individual in its normal

activities of food gathering, mating, and caring for young” (Burt 1943). For birds, as

most species, home range size is a function of many factors including food availability,

cover and protection from predators, nest site availability, availability of singing perches,

bird density, competition, and the age and size of the bird (Fretwell and Lucas 1970,

93

Mazarolle and Hobson 2004, Petit and Petit 1996, Smith and Shugart 1987, Wilson

1979). Home range size varies in differing quality habitats, with poor quality habitat

resulting in the need for larger territory size and thus, lower bird density at a site

(Mazarolle and Hobson 2004).

The objectives of this portion of the study were to test for differences in home

range, habitat use, and nesting success of two focal songbird species among different

silvicultural treatments used to reduce tree basal area in Bankhead National Forest,

Alabama.


Study Area


Forest (Fig. 4.1), located in Lawrence and Winston counties, northwestern Alabama.

Bankhead National Forest (BNF) is a 72,800 ha multi-use forest located in the southern

Cumberland Plateau (Gaines and Creed 2003). The physiography of this region consists

of flat plateaus dissected by small valleys. The forests in this region have a diverse

species composition due to a variety of past disturbances – agriculture in the 1800s,

heavy cutting and wildfire in the early 1900s, fire suppression in the last decade and the

recent infestation of the southern pine beetle (Dendroctonus frontalis Zimmerman)

(Gaines and Creed 2003). In the 1930’s, abandoned farm land and other open lands were

reestablished with loblolly pine, Pinus taeda Linnaeus (Gaines and Creed 2003). This

94

has resulted in 31,600 ha of loblolly pine throughout BNF. Once established, intensive

pine plantation management was not implemented, and subsequently, a variety of

hardwood species voluntarily invaded these sites. Over the past decade, southern pine

beetle infestations have killed a major portion of loblolly pine, increasing fuel loads and

the risk of wildfires (Gaines and Creed 2003). Bankhead National Forest has initiated a

Forest Health and Restoration Project to promote healthy forest growth via thinning and

fire disturbance. The thinning and fire prescriptions were administered to return the

forest to a mixed oak-pine upland ecosystem. My research was conducted in conjunction

with Bankhead National Forest’s restoration project.

Figure 4.1. Location of study plots in Bankhead National Forest, AL.

Burning treatment

Burn No Burn

Control 3 3

Thin 6 6

Figure 4.2. Experimental design: two-factor, randomized

complete block design. Treatments include two burn

treatments and two thinning levels.

95

The study design consisted of a randomized complete block design with two

factors – three thinning levels (no thin, 11 m2 ha-1 residual basal area, and 17 m2 ha-1

residual basal area) and two burn treatments (no burn and burn). Each treatment was

replicated three times and were blocked by year. Treatments were assigned randomly to

delineated stands. After the treatments were completed, I decided to collapse the thinned

treatments together because there was no difference in basal area between the two

thinning levels (analysis of variance, F = 0.066, df = 1, p = 0.8). Although this was not

the response variable I was studying, the variability within the individual treatment levels

was uneven, with some stands within the same treatment level having greater BA than the

target and others having lower BA than the target. This variation was too large to detect

any difference between the thinning levels. This resulted in three replicates each of the

control and burn, and six replicates each of the thin and the thin/burn (Fig. 4.2). The

research stands were located on upland sites composed of 20 to 35 year old loblolly pine.

Stands were comprised of a minimum of sixty percent pine (loblolly pine or Virginia

pine, P. virginiana Mill.), with the remainder mainly oak species (Quercus spp.).

Average stand size was 12 ha and plots had similar age and stand density. Thinning

favored the retention of hardwood species and was done before fire prescriptions.

Prescribed burning was completed in the dormant season (January – March) with low-

burning surface fires.

Treatments on block one were completed between August 2005 and February

2006; blocks two and three were treated between April 2006 and March 2007. Post-

treatment data were collected from block one between April and August 2006, and from

blocks two and three between April and August 2007.

96

Target Species

I selected the hooded warbler (Wilsonia citrina Boddaert) and the worm-eating

warbler (Helmitheros vermivorus Gmelin) as target species. These two species were

relatively common in the stands before treatment (see Chapter 2), are insectivorous, and

their nests are relatively easy to find. Hooded warblers are small (11 g) forest-interior

birds that inhabit mixed hardwood forests and cypress-gum swamps (Evans-Ogden and

Stutchbury 1994). They use small clearings and a shrub understory for nesting and often

place nests at the forest edge or in tree fall gaps (Evans-Ogden and Stutchbury 1994).

Worm-eating warblers are also small (12-14 g) forest-interior birds that inhabit

deciduous and mixed forests (Hanners and Patton 1998). The primary factor in their

presence in an area is the availability of slopes for nesting (Hanners and Patton 1998).

Sampling

Radiotelemetry. I captured males of each target species using song playback to

attract them into mistnets. I banded each captured bird with a U.S. Fish and Wildlife

Service aluminum band and plastic color bands to aid in individual identification. I also

attached a radio transmitter (model BD-2, 0.065 g [4-5% of body mass], battery life:

approx. 21 days, Holohil Systems, ltd.) to the back of selected males using a figure-8

harness made with cotton thread (Rappole and Tipton 1991) and secured with glue

(Krazy Glue, Columbus, OH). I released all birds immediately after processing and

waited 24 h to track them to allow for adjustment to leg bands and radio transmitters.

I used burst sampling methods (Barg et al. 2005) when tracking birds, recording

bird locations at 60 second intervals for a total of 30 points per session. If the bird was

lost during the session, I temporarily stopped recording until the bird could be relocated.

97

Each session lasted between 30 and 80 minutes. I tracked each bird every three to four

days, performed as many sessions as possible before the transmitter battery died. Each

location was recorded using a handheld global positioning system (GPS) (eTrex Vista,

Garmin Ltd.) and was downloaded into ArcGIS v. 9.1 (ESRI) for analysis.

Reproductive success. I searched for nests and watched for indications of

reproductive success while radio tracking. When a nest was found, I recorded its location

using GPS and marked the nest with flagging at least 3m away. I monitored nests based

on the standard protocol of Ralph et al. (1993). Nests were checked every 3-4 days and

more often when fledging was expected. At each nest check, I recorded the activity of

the adult, contents of nest, and age of young, as well as any indications of predation or

nest parasitism. To reduce the risk of increasing predation and nest parasitism, I took

precautions detailed in Martin and Geupel (1993) and Ralph et al. (1993).

Microhabitat. I measured microhabitat variables at the end of each breeding

season at 11.3 m radius (0.04 ha) circular plots, using methods based on James and

Shugart (1970). I completed three habitat plots at random points within each territory

and outside of each territory (Smith and Shugart 1987). Random points were determined

using Hawth’s tools random point generator. I also completed a habitat plot at each nest

location. At each plot I recorded the species, size class (7.6-33 cm, 33.1-58.4 cm, 58.5-

83.8, >83.9 cm diameter at breast height [DBH]). At a smaller plot (5 m radius) within

the larger plot I tallied the number of woody and herbaceous stems. Within a 1 m radius

circle within the 5 m circle I recorded percent ground cover. I recorded aspect, percent

slope (using a percent scale clinometer, to nearest percent), percent canopy cover (using a

convex spherical densitometer, to nearest percent) and litter depth (to nearest mm) at the

98

center point of the plot. At the four cardinal directions 5 m from the plot center I

measured percent canopy cover (using a convex spherical densitometer, to nearest

percent) and percent vertical cover from ground level to 3 m (using a checkered drop

cloth, to nearest percent).

Data analysis

Home range delineation. I only used birds that had greater than three observation

sessions and 70 individual observation points for the home range analyses to ensure an

adequate sample size. For each bird, I selected the home range model that had the most

support from the data based on likelihood cross-validation (Horne and Garton 2006)

using Animal Space Use v.1.2 (Horne and Garton 2007). The “best” model was defined

as the model with the smallest Kullback-Leibler distance (i.e., difference between actual

and estimated distributions). This approach allows information-theoretic model selection

to assist in deciding which approximating model is closest to the underlying distribution

of the individual, using the data collected from that individual (Horne and Garton 2006).

The home ranges models I used in the selection process were the exponential power

model, one mode bivariate normal, two mode bivariate circular, two mode bivariate

normal, fixed kernel density, and adaptive kernel density. The exponential power model

is a simple model that is circular in shape and flat on top. It is the most economical home

range, where the animal uses the habitat within the home range uniformly (Horne and

Garton 2006). For the bivariate circular model, the center of activity is first calculated

using the means of all locations. The radius (r) is then calculated from this center of

activity. This model assumes observations decline in density from the center to the edge

of the distribution (Calhoun and Casby 1958). An improvement on this method is the

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bivariate normal model which applies an elliptical approximation. This model is based on

the assumption of an underlying normal, or bell-shaped, distribution (Jennrich and Turner

1969). Kernel density estimators are equitable to the histogram, the oldest density

estimator. Kernels or ‘bumps’ are calculated based on number of observations in a given

location; the more observations, the ‘higher’ the bump will be and the greater the

probability of the animal occurring in that location (Worton 1989). Animal Space Use

v.2.1 (Horne and Garton 2007) was used to create the home ranges after I chose the

model. Core areas were defined as the area within the 95% home range boundary with

the probability of use greater than that expected from a uniform distribution of use

(Samuel et al. 1985). This was the location where the difference between the actual

home range and the expected uniform home range was the greatest. To test for home

range and core area size differences among treatments I used a Kruskall-Wallace test

(SPSS v.15.0)

Reproductive success. Sample size was too small to evaluate nesting success

using the Mayfield index (Mayfield 1961). I instead used the method developed by

Vickery et al. (1992b) to create a reproductive index based on behaviors indicative of

different stages of the breeding cycle. Behaviors were ranked as follows: (1) territorial

male present > 4 weeks or a nest parasitized by a brown-headed cowbird, (2) territorial

male and female present > 4 weeks, (3) evidence of a nest, and (4) evidence of fledging

success. Nest success was defined as fledging at least one young. This method requires

that sampling efforts are equal among individuals to avoid bias (Vickery et al. 1992b). I

was unable to do so because of manpower limitation, so the presented results should be

100

regarded as coarse estimates. I tested for differences in reproductive index among

treatments with a Kruskall-Wallace test (SPSS v.15.0).

Microhabitat. I averaged all variables across three habitat plots for each bird

territory and paired random locations. To reduce the number of variables in the model

and avoid multicollinearity, I use principle components analysis (PCA, SPSS v.15.0).

From each component, I chose one variable to represent that component in the analysis. I

used these variables instead of the principle components so that the results would be

easier to interpret. I inspected variables for multicollinearity using Pearson’s correlation

matrix and for multivariate outliers using Mahalanobis distance. I then used pairwise

logistic regression (PROC LOGISTIC, SAS v. 9.1) to create a set of habitat models for

each species. To assess the relative degree of fit for each model, I used Akaike’s

Information Criteria (Burnham and Anderson 1998). The best model was selected by

judging the degree of support as indicated by delta AIC and normalized Akaike weights.

Models with delta AIC < 2 were considered to have substantial support (Burnham and

Anderson 1998).

Results

Home range. Over the two years, 23 birds were tracked (13 hooded warblers and

10 worm-eating warblers). The treatment with the most individuals of either species was

the thinned stands, and I was not able to track any birds on the burned stands because of

the low occurrence of the species on the burned stands (Table 4.1). The average number

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Treatment HOWA WEWA Total

Control 2 2 4

Burn 0 0 0

Thin 8 4 12

Thin/Burn 3 4 7

Total 13 10 23

Table 4.1. Distribution of radio-tracked hooded warblers (HOWA) and

worm-eating warblers (WEWA) among silvicultural treatments in

Bankhead National Forest, AL, one year post-treatment, 2006-2007.

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of observation points of each bird was 128, from an average of 5.6 observation sessions

per bird. The exponential power model was the ‘best’ model for 15 birds (nine hooded

warblers and six worm-eating warblers), bivariate normal model for seven birds (three

hooded warblers and four worm-eating warblers), and the two mode bivariate circular

model for one bird (hooded warbler). Neither home range nor core area differed among

treatments for either species (Table 4.2). Home ranges for hooded warblers ranged from

3.4 ha to 13.1 ha and from 4.3 ha to 8.8 ha for worm-eating warblers (Table 4.2). Home

ranges overlapped; however core areas did not overlap in the same species. All core

areas were located off the treated stands but in some cases, parts of the home range were

located on the stand (Fig. 4.3).

Microhabitat. The original 18 variables showed low multivariate correlation

(Kaiser-Meyer-Olkin [KMO] Measure of Sampling Adequacy = 0.226) so I removed the

two variables with the lowest multivariate correlation (log cover and rock cover) from the

principle component analysis to increase the KMO measure of sampling adequacy to

0.552. The principle component analysis on the remaining sixteen habitat variables

generated seven principle components (PCs) with eigen values greater than one. The first

was represented by litter cover, the second by number of woody stems, the third by

herbaceous cover, the fourth by litter depth, the fifth by bare ground cover, the sixth by

vertical cover, and the seventh by tree abundance (Table 4.3). All retained components

had an eigen value greater than 1. The seven components retained approximately 73% of

the original variation (Bartlett’s Test of Sphericity χ2 = 405.657, df = 120, p < 0.001).

Log cover showed high multicollinearity, so it was eliminated from the analysis and rock

cover was used to represent ground debris. The variables included in the analyses were

103

Kruskall-Wallace test Mean by treatment

Variable χ2 df p Control Thin Thin/Burn

Hooded Warbler

Home Range 0.92 2 0.63 5.44±.5.44 13.05±6.16 3.41±3.01

Core Area 0.66 2 0.72 2.19±2.08 5.84±2.75 2.60±2.41

Worm-eating Warbler

Home Range 1.32 2 0.52 4.38±0.53 4.53±2.61 8.81±8.81

Core Area 0.94 2 0.62 1.88±0.34 2.15±1.19 3.01±1.21

Table 4.2. Significance values, mean, and standard error among silvicultural treatment

for home range and core area (ha) of hooded warblers (HOWA) and worm-eating

warblers (WEWA) in Bankhead National Forest, AL, 2006-2007.

104

Figure 4.3. Example of 95% probability home range locations in relation to treatment plot

for hooded warbler (HOWA) and worm-eating warbler (WEWA). Inner darker portion

of home range is the bird’s core area. Small circles are individual bird locations.

105

PC1 PC2 PC3 PC4 PC5 PC6 PC7

Tree abundance 0.205 0.669 0.153 0.160 0.057 0.353 0.165

Tree spp. Richness 0.643 -0.450 0.148 0.057 0.280 -0.090 -0.026

# snags 0.166 -0.054 -0.223 0.172 -0.285 -0.672 0.388

# woody stems 0.011 0.645 -0.494 0.025 -0.019 -0.032 -0.201

# herb stems -0.398 0.220 0.686 -0.028 -0.065 -0.017 -0.072

Bare ground -0.464 0.137 -0.225 0.333 0.629 -0.056 0.211

Litter cover 0.818 -0.026 -0.138 0.066 -0.315 0.033 -0.043

Rock cover 0.082 -0.148 0.034 0.407 0.037 -0.255 -0.440

Log cover -0.373 -0.396 -0.232 -0.192 -0.246 0.308 0.024

Herb cover -0.392 0.002 0.750 -0.071 -0.018 -0.249 -0.082

Fern cover -0.039 0.048 0.179 0.307 -0.418 0.340 0.519

Woody cover -0.034 0.645 -0.093 -0.467 -0.057 0.002 -0.242

Tree cover 0.301 -0.089 0.035 -0.458 0.347 0.027 0.297

Slope 0.399 0.071 0.080 0.223 -0.256 0.052 -0.330

litter depth 0.468 -0.277 0.062 -0.609 -0.008 0.043 -0.015

Basal area 0.684 0.203 0.143 0.111 0.360 0.063 0.049

Canopy cover 0.755 0.194 0.303 0.193 0.038 0.067 0.052

Vertical cover -0.115 -0.497 -0.074 0.283 0.128 0.460 -0.233

Eigenvalue 3.35 2.15 1.67 1.46 1.24 1.15 1.06

% Variance 18.60 11.94 9.26 8.09 6.86 6.41 5.87

Table 4.3. Principle component analysis loadings, eigenvalues, and percent

variance for microclimate variables following silvicultural treatment in

Bankheand National Forest, AL, 2006-2007.

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the above seven variables (which represented the corresponding principle component)

and rock cover. I used the following six logistic regression models in the AIC analysis:

(1) full model (all variables); (2) all variables except rock cover; (3) foliage ground

cover: woody stems and herbaceous cover; (4) ground cover: litter depth, litter cover,

bare ground; and (5) structure: vertical cover and tree abundance. I included a sixth

model (slope) for worm-eating warblers because slope is known to be an important

component for nesting (Evans-Ogden and Stutchbury 1994). When rock cover was

included in the model with all the variables, there appeared to be high multicollinearity

with the other variables (indicated by high confidence intervals). The best fitting models

for the worm-eating warbler was the structure model (model # 1), containing vertical

cover and tree abundance variables and the slope model (model # 2) (Table 4.4). The

models containing (1) all variables and (2) all variables except rock cover were the best

fitting models for the hooded warbler (Table 4.4). The model without rock cover was

slightly better than the model with all variables (Table 4.4).

Reproductive success. Fourteen nests were found over the two years; 11 worm-

eating warbler nests and three hooded warbler nests. Only five of the nests were located

in treated stands, the others were located adjacent to stands, but in areas that were not

treated. The two worm-eating warbler nests on the burned stands were successful and the

two nests on the thinned stands fledged only brown-headed cowbirds. The one nest

found on the control failed. Of the nests that were located adjacent to the stands, three

fledged young, five failed, and the outcome of one was unknown. For the 14 nests we

monitored, nest success rate was 36%.

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Model

P-value AIC

Delta

AIC

Akaike

weight

Worm-eating Warbler

1 Structure (tree abundance, vertical cover) 0.01 15.65 0.00 0.90

2 Slope (slope) 0.01 16.45 0.80 0.38

3

All variables (tree abundance, woody stems, bare ground cover, litter ground

cover, rock ground cover, herbaceous ground cover, litter depth, vertical cover)

0.03 20.94 5.29 0.06

4 All variables except rocks 0.09 23.73 8.08 0.02

5 Foliage ground cover (woody stems, herbaceous ground cover) 0.32 23.90 8.25 0.01

6 Ground cover (bare ground cover, litter ground cover, litter depth) 0.65 26.53 10.88 0.00

Hooded Warbler

1 All variables except rocks <0.01 14.07 0.00 0.68

2

All variables(tree abundance, woody stems, bare ground cover, litter ground

cover, rock ground cover, herbaceous ground cover, litter depth, vertical cover)

<0.01 16.05 1.98 0.25

3 Structure (tree abundance, vertical cover) 0.03 19.11 5.05 0.05

4 Foliage ground cover (woody stems, herbaceous ground cover) 0.12 21.93 7.86 0.01

5 Ground cover (bare ground cover, litter ground cover, litter depth) 0.99 28.10 14.03 0.00

Table 4.4. AIC scores for five logistic regression models of habitat preferences of hooded warblers and worm-eating warblers in


107

108

I used the behavior of thirty-nine birds (21 worm-eating warblers and 18 hooded

warblers) to calculate reproductive indices. Reproductive index was not different among

treatments for either species (χ2=0.67, df =2, P = 0.72 for worm eating warblers; χ

2=5.10,

df =2, P = 0.08 for hooded warblers).

Discussion

Hooded and worm-eating warblers appear to prefer habitat that is adjacent to the

treated stands in this study. No bird’s home range was entirely located in any of the

treated stands, although some birds had territories that were partially located on the

treated stands. None of the birds’ core areas were located in the stands, indicating that

the stands do not provide habitat crucial for either species. The majority of the home

ranges for both species were located in the small ravines and gullies that surround all of

the stands. These were areas within the boundaries of the treatment that were not treated,

or areas adjacent to the treatment. There was no difference in home range size or core

area among treatments for either species; however it may not be appropriate to make

comparisons among the treatments since the majority of the home ranges were not

located in treated stands.

The three probability distributions (exponential power, one mode bivariate

normal, and one mode bivariate circular) that were the best fit for the two warbler species

describe distributions of animals inhabitating homogeneous habitats (Van Winkle 1975).

This indicates birds are using habitat within their home range in a spatially uniform

manner. The bivariate normal model is characterized by a distribution that is elliptical,

where occurrence probability varies in direction from the home range center (Van Winkle

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1975). The exponential power and bivariate circular models are described by the

probability of occurrence at distances from the home range center, without regard to

direction (Horne and Garton 2006, Koeppl et al. 1975). Thus, habitat use by these two

species is relatively uniform within the home range and there are not multiple areas of

concentrated use.

Our home range size estimations for hooded warblers were larger than territory

sizes previously reported. There are no studies that report home range size estimates for

hooded warblers. In Pennsylvania, average territory size was 0.88 ha (Howlett and

Stutchbury 1997). They estimated territory size by recording locations of singing males

but failed to describe the method used for delineating territories. Since they estimated

territories based on singing birds, it is expected that their estimates would be smaller than

the home range estimates in this study. Norris and Stutchbury (2001) recorded extra-

territorial movements by male hooded warblers and found that they will travel up to 465

m, usually to attain extra-pair copulations with neighboring females. Roughly combining

this distance with their previous estimates of singing territory size (the two studies were

in the same location) provides insight into the home range size of birds in their study

area. These approximations are close to the home range size estimates in this study (3–13

ha).

Hooded warblers are socially monogamous birds, however extra-pair matings

(revealed via DNA fingerprinting) are a common and important component of their

mating system (Evans-Ogden and Stutchbury 1994). When hooded warbler densities are

low, as they are in our study area, it is expected that home range size would increase due

to males traveling farther in search of extra pair copulations.

110

Worm-eating warbler home ranges were larger than territory size previously

reported in the literature. Hanners and Patton (1998) reported a mean territory size of

1.72 ha in Connecticut, although they did not indicate how the data were collected or how

territories were delineated. If it was based on the bird’s singing territory, I would expect

it to be slightly smaller than the bird’s home range. Their measure may coincide more

appropriately with the core areas delineated in my study.

Home range size and quality can be influenced by a variety of factors, including

food abundance; predator abundance; bird density; and availability of nest sites

(Mazarolle and Hobson 2004, Marshall and Cooper 2004, Petit and Petit 1996, Smith and

Shugart 1987). Generally, poor quality habitat results in the need for a larger home range

(Mazarolle and Hobson 2004). Since there is little information available about home

range size for these two species, it is difficult to make assumptions about the quality of

their habitat. Based on rough estimates, it appears that home ranges coincide with other

studies.

Hooded warblers are considered forest interior species, but also have

requirements associated with forest openings and canopy gaps (Evans-Ogden and

Stutchbury 1994, Kilgo et al. 1996, Moorman et al. 2002, Whittam et al. 2002). It

appears that hooded warblers are choosing habitat based on many variables in this study.

Their probability of occurrence increases when herbaceous ground cover and vertical

cover increases. Other studies have reported an association of hooded warblers with

dense understory vegetation (Mooreman et al. 2002, Whittam et al. 2002). Kilgo et al.

(1996) reported that hooded warblers in South Carolina preferred shrubs with thicket-

forming properties that provide protection from weather and predators. It is likely that as

111

shrub recovery advances and provides more resources, hooded warbler densities will

increase.

Habitat structure in the forest understory and slope appear to be important in

predicting the presence of worm-eating warblers. In Missouri, worm-eating warblers

preferred large forests with dense understory (Wenny et al. 1993). Watts and Wilson

(2005) concluded that dense shrub cover was more important for worm-eating warbler

habitat than plant composition or any other factor, including slope. Slope is considered to

be an important factor in the presence of worm-eating warblers because they only place

their nests on slopes (Gale et al. 1997, Hanners and Patton 1998, Wenny et al. 1993).

The nests I found were all located on some sort of slope, but not necessarily a long slope.

We found nests on the slopes along side logging roads and on slopes created by up-rooted

trees, as well as hillside slopes. In coastal North Carolina, a very flat terrain, worm-

eating warblers are present in very high densities (Watts and Wilson 2005). It appears

that dense shrub cover is an important habitat feature for worm-eating warblers and the

presence of slope is secondarily important.

Reproductive estimates for both species were low; however, small sample size

and deviation from standard protocols (i.e., not spending equal amounts of time

observing each bird) may have biased these results. For the 14 nests I found, nest success

rate was 36%, considerably lower than nest success reported in other studies. Reported

nest success rates are around 50% for hooded warblers (Howlett and Stutchbury 1997,

Moorman et al. 2002, Whittam et al. 2002) and 76% for worm-eating warblers (Gale et

al. 1997). Of the five nests found in the stands (all worm-eating warbler nests), only two

nests fledged young. Both of these nests were in burned stands. The nests on the thinned

112

stands fledged only cowbirds and the nest found on the control failed due to predation.

After the nest failed, the pair could not be located in the stand and appeared to have left

the area completely.

Average reproductive index shows that there were limited observations of

reproductive behavior, especially in hooded warblers. Evidence of hooded warbler

reproduction was seen only on and adjacent to thinned stands. I never observed any

reproductive evidence other than the presence of territories for birds on or adjacent to the

untreated or thinned/burned stands. Evidence of worm-eating warbler reproduction was

seen on or adjacent to all treated stands, indicating that they may be more flexible in their

choice of nesting habitat than hooded warblers. Neither species were seen with fledglings

in the treated stands, only adjacent to them, so again, it may not be appropriate to make

comparisons among the treatments.

Stuart-Smith and Hayes (2003) found that increased density of residual trees

increased the odds of predation of artificial nests. Other studies have also suggested that

greater structural diversity in regenerating plots may provide habitat for a greater number

of avian nest predators (Barber et al. 2001). There was greater structural diversity in

thinned stands in our study as well, so this may have resulted in the same effect. More

nest predators would naturally lead to lower nest success rates. High structural diversity

also creates more perching sites for use by brown-headed cowbirds (Molothrus ater

Boddaert). Cowbirds use perches in above an open forest canopy to watch and locate

nests to parasitize (Brittingham and Temple 1996, Evans and Gates 1997). Most female

cowbirds travel less than three km between their agricultural feeding grounds and

breeding areas, although some will travel farther (Goguen and Mathews 1999). This

113

results in higher cowbird densities in fragmented landscapes. Although cowbird

abundance increased slightly in the stands after thinning, density is still relatively low. In

this study, stands are located within a large contiguous forest which may minimize the

presence of cowbirds, however if more areas are thinned and more edges are created, it is

likely the cowbird density will increase (Evans and Gates 1997).

Bankhead National Forest is a large contiguous forest; the treatments examined in

this study created relatively small openings and were not the dominant landscape feature.

The landscape mosaic created by cutting small portions of forest may provide hooded

warblers and worm-eating warblers with the types of habitat they require in the short

term. By staggering treatments over time and space, continuous habitat would be

provided for these species.

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CHAPTER 5

CONCLUSION AND MANAGEMENT RECOMMENDATIONS

No forest management practice can be generalized as either detrimental or

beneficial; some species respond positively and other respond negatively. Change in the

bird community will continue as forest succession progresses. The results from my

study suggest that early-successional, interior/edge habitat specialist responded positively

to thinning treatments in the short term. To a lesser extent, burning treatments also

resulted in a positive response by early successional, interior/edge species. While

interior/edge species responded positively, neither interior nor open/edge species

responded negatively. The change in habitat available to the bird community was not so

drastic that interior species were no longer able to use the habitat.

Pre-treatment characteristics consisted of thick pine stands with gaps and edges

created by SPB damage, power line throughways, roads, and fields. These conditions

provided habitat for many forest interior and interior/edge bird species. One year after

thinning, stands were more open and provided habitat for interior/edge and edge/open

species. Thinned stands were characterized by an understory that provided habitat for

many shrub nesting species. Prescribed burning had a smaller effect on the habitat and

bird community. Burned stands were similar in habitat and bird community to the

untreated plots. Because all trees were retained in these stands, the bird community

remained fairly consistent between pre and post treatment. Thinning and burning in

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combination created a habitat that was quite similar to the thinned stands, except that

burned/thinned stands had a greater loss of litter cover. There was an increase in edge

and open habitat species in thinned and burned stands and a decrease in foliage foraging

species. Thinned/burned stands were similar to thinned stands in habitat and bird

community. Burning only affected the litter layer, decreasing the amount of litter ground

cover and the litter depth. Neither of theses habitat characteristics were highly correlated

with the bird community in this study, so there was a limited impact on the bird.

Greenberg et al. (2007) and Stribling and Barron (1995) found that understory fuel

reduction treatments (low intensity fire and understory removal) have few detectable

effects on breeding birds. Shrub nesters were most common on light intensity burns in

other studies (Greenberg et al. 1995, Stribling and Barron 1995, Wilson et al. 1995). It

appears that thinning has a greater impact on the bird community than does low-intensity

burning. My results suggest that, one year after treatment, thinning creates habitat for

interior/edge species (species that use early-successional habitat) without displacing

many of the interior forest birds. Other studies have also come to this conclusion

(Campbell et al. 2007, Costello et al. 2000, Holmes and Pitt 2007, Vanderwel et al.

2007).

Individual use of the plots by hooded warblers and worm-eating warblers indicate

that, one year after treatment, the thinned stands create habitat that is used marginally by

these species, but is not causing either species to leave. Most of the home ranges were

located in the small ravines and gullies that surround the stands with only a small portion

of the bird’s home range in the treated stand. It appears that the habitat available in these

areas provide more suitable habitat than what is available in the treated stands. Habitat

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that hooded warblers are using is characterized by high herbaceous ground cover and

vertical cover. Worm-eating warbler habitat is characterized by dense understory

vegetation and the presence of slopes. Since there are no previous studies examining

home range size of either species, I cannot make comparisons.

Management Recommendations

Management recommendations made as a result of this research are limited in

their scope. This research was conducted in a large contiguous forest on the southern

Cumberland Plateau; the treatments examined in this study created relatively small

openings and were not the dominant landscape feature. It is uncertain what effect the

treatments would have in a smaller, fragmented landscape; if the treatments were applied

over larger or smaller stands; or of the treatments were used outside of this ecoregion.

Although this is a well designed experimental study, the nature of wildlife studies

limits replication. Limited replication in this study may be a limiting factor in detecting

response to ecological processes (Marzluff et al. 2000).

I collected one year post treatment data for this study, and although I detected

some changes in the bird community, it will change over time as shrubs recover and other

habitat attributes continue to change. Long term data needs to be collected to examine

trends in the bird community as the plots recover from disturbance. There are few long-

term studies of the effects of forest management on birds, and understanding long term

trends is as important as understanding short term trends (Marzluff et al. 2000, Thompson

et al. 2000). As succession progresses, the resources available to birds will differ, and

this will alter the bird community (Greenberg et al. 2007, Harrison et al. 2005, Holmes

120

and Pitt 2007, Jobes et al. 2004, Yahner 1997). Some studies suggest there is a lag time

between treatment implementation and changes in the bird community, so one year of

data can sometimes be misleading (Greenberg et al. 2007, Jobes et al. 2004).

With those caveats in mind, I recommend tree thinning as a viable option for

creating habitat for early-successional bird species. It is a particularly attractive method

if clear cutting is not an option and/or retaining interior forest birds is included a

management goal. However, thinned forests create early-successional habitat that is

ephemeral, so I recommend that thinning be used at different intervals across the

landscape to provide early successional habitat throughout the forest. The landscape

mosaic created by cutting small portions of forest may provide early successional species

with the types of habitat they require in the short term while also retaining many of the

interior forest birds. By staggering treatments over time and space, continuous habitat

would be provided for these species.

Bibiography

Campbell, S.P., J.W. Witham, M.L. Hunter, Jr. 2007. Long-term effects of group-

selection timber harvesting on abundance of forest birds. Conservation Biology 21:

1218-1229.

Costello, C.A., M. Yamaski, P.J. Pekins, W.B. Leak, C.D. Neefus. 2000. Songbird

response to group selection harvests and clearcuts in a New Hampshire northern

hardwood forest. Forest Ecology and Management 127: 41-54.

Greenberg, C.H., L.D. Harris, D.G. Neary. 1995. A comparison of bird communities in

burned and salvaged-logged, clearcut, and forested Florida sand pine scrub. Wilson

Bulletin 107: 40-45.

Greenberg, C.H., A.L. Tomcho, J.D. Lanham, T.A. Waldrop, J. Tomcho, R.J. Phillips, D.

Simon. 2007. Short term effects of fire and other fuel reduction treatments on

121

breeding birds in a Southern Appalachian upland hardwood forest. Journal of Wildlife


Harrison, R.B., F.K.A. Schmiegelow, R. Naidoo. 2005. Stand-level response of breeding

forest songbirds to multiple levels of partial-cut harvest in four boreal forest types.

Canadian Journal of Forest Resources 35: 1553-1567.

Holmes, S.B. and D.G. Pitt. 2007. Response of bird communities to selection harvesting

in a northern tolerant hardwood forest. Forest Ecology and Management 238: 280-

292.

Jobes, A.P., E. Nol, D.R. Voigt. 2004. Effects of selection cutting on bird communities in

contiguous eastern hardwood forests. Journal of Wildlife Management 68: 57-60.

Marzluff, J.M., M.G. Raphael, R. Sallabanks. 2000. Understanding the effects of forest

management practices on avian species. Wildlife Society Bulletin 28: 1132-1143.

Stribling, H.L., M.G. Barron. 1995. Short-term effects of cool and hot prescribed burning

on breeding songbird populations in the Alabama Piedmont. Southern Journal of

Applied Forestry 19: 18-22.

Thompson, F.R. III, J.D. Brawn, S. Robinson, J. Faaborg, R.L. Clawson. 2000.

Approaches to investigate effects of forest management on birds in eastern deciduous

forests: How reliable is our knowledge? Wildlife Society Bulletin 28: 1111-1122.

Vanderwel, M.C., J.R. Malcom, S.C. Mills. 2007. A meta-analysis of bird responses to

uniform partial harvesting across North America. Conservation Biology 21: 1230-

1240.

Wilson, C.W., R.E. Masters, G.A. Bukenhofer. 1995. Breeding bird response to pine-

grassland community restoration for red-cockaded woodpeckers. Journal of Wildlife


Yahner, R.H. 1997. Long term dynamics of bird communities in a managed forested

landscape. Wilson Bulletin 109: 595-613.

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VITA

Jill Wick, daughter of Norm and Diane Wick, was born May 11th

1979 in Two

Rivers, Wisconsin. She attended University of Wisconsin at Stevens Point for her

undergraduate education in the Wildlife Biology department and earned her BS in 2002.

She moved to Alabama in 2005 to begin her avian research and will graduate in May of

2008. She has since secured a position in Albuquerque New Mexico at an environmental

consulting firm.

forest disturbance: breeding ecology … publications/thesis...forest disturbance: breeding ecology...

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