use of reclaimed surface mine grasslands by northern harriers, short-eared...
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USE OF RECLAIMED SURFACE MINE GRASSLANDS BY NORTHERN
HARRIERS, SHORT-EARED OWLS, AND OTHER RAPTORS:
ABUNDANCE, BEHAVIOR, AND NESTING SUCCESS
Mark Vukovich Bachelor of Science
University of North Carolina at Asheville Asheville, NC
May 2000
Submitted to:
Faculty of the Graduate School of Eastern Kentucky University in partial fulfillment of the requirements for the degree of
Master of Science May 2004
Dedicated to my grandparents, Antonia and Lucas Vukovich, and my brother,
Robert David Vukovich
I
Acknowledgments
I would like to acknowledge my advisor, Dr. Gary Ritchison, for giving me this project.
His encouraging words, guidance, and humor made this project a valuable and
memorable learning experience. I would like to thank the Kentucky Department of Fish
and Wildlife Resources (KDFWR) for funding this study. In addition, special thanks to
the Department of Biological Sciences (Jones Award) at Eastern Kentucky University,
the Kentucky Ornithological Society (Monroe Fund), and the Somerset Bird Club for
providing additional funding. I would like to thank KDFWR personnel, particularly Joy
Fitzgerald, Shawchyi Vorisek, and Doug Wehr, for their assistance. A debt of gratitude
goes to my field assistants, Bradley Davis, Matt Giovanni, Mark Monroe, Jacob Stewart,
and Ben Sutter. I would like to thank my committee members, Dr. Charles Elliott and
Dr. Guenter Schuster. I would also like to acknowledge David Barber, Dr. Keith
Bildstein, Lauren Lawson, Joy O'Keefe, Brainard Palmer-Ball, and Dr. James Petranka
for advice and support before and during the project. I would especially like to thank my
family for their love and support during this project.
II
Abstract
Grasslands are among the most threatened habitats in North America, and, as a
result, populations of many grassland birds, including Short-eared Owls (Asio flammeus)
and Northern Harriers (Circus cyaneus), are declining. Several factors, including the
conversion of grasslands to croplands, disrupted fire regimes, and increased
fragmentation, have likely contributed to these declines. While native grasslands are
disappearing, current procedures for reclaiming surface mines have produced large areas
of ‘reclaimed’ grasslands in the eastern United States. Currently, little is known about the
use of such grasslands by raptors. The objectives of this study were to (1) determine the
relative abundance of Short-eared Owls, Northern Harriers, and other raptors on a
reclaimed surface mine, (2) examine the hunting behavior of Short-eared Owls and
Northern Harriers for comparison to that reported at other locations, and (3) examine the
nesting behavior of Northern Harriers. This study was conducted from January 2002-
July 2003 on reclaimed surface mine grasslands located in the Peabody Wildlife
Management Area in Ohio and Muhlenberg counties, Kentucky. Forty-nine surveys were
conducted along a 51.4 km route. Short-eared Owl and Northern Harrier abundance on
the Peabody WMA was among the highest reported in midwestern United States. Raptor
diversity on the Peabody WMA was impressive during the survey (N = 15 species) and
study (N = 19). Prey availability and weather may affect numbers of non-breeding and
breeding raptors between years on the Peabody WMA. Hunting behavior was observed
from January 2002 - March 2003. Hunting success of Northern Harriers (7%) and Short-
eared Owls (10.9%) on the Peabody WMA was comparable to other studies. Analysis
revealed that Short-eared Owls hunted more often in areas with shorter, less dense
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vegetation. From April - July 2002-03, an effort was made to locate nests. I documented
the greatest number of Northern Harrier nests (N = 46) in Kentucky during this study.
Reproductive success of Northern Harriers on the Peabody WMA (21.7%) was among
the lowest reported in North America. Successful nests were located in taller, denser
vegetation compared to unsuccessful nests. Predators may be more abundant in drier
upland habitats compared to wetter habitats. While these results indicate that reclaimed
surface mine grasslands can provide breeding habitat for Northern Harriers, additional
work is needed to determine if harriers nesting in such areas represent population sources
or sinks.
IV
Table of Contents
Introduction....................................................................................................................... 9
Study site ................................................................................................................. 11
Chapter 1. Populations of Raptors on the Peabody Wildlife Management Area –
Road Surveys................................................................................................................... 13
Methods........................................................................................................................ 13
Data Analysis .......................................................................................................... 15
Results .......................................................................................................................... 18
Survey results .......................................................................................................... 18
Habitat use .............................................................................................................. 22
Behavior .................................................................................................................. 23
Discussion .................................................................................................................... 24
Survey results .......................................................................................................... 24
Habitat Use and Foraging Behavior....................................................................... 28
Other Raptors Observed During Road Surveys ........................................................... 29
Mississippi Kite ....................................................................................................... 29
Swallow-tailed Kite ................................................................................................. 30
Sharp-shinned Hawk ............................................................................................... 30
Cooper’s Hawk........................................................................................................ 30
Red-shouldered Hawk ............................................................................................. 31
Broad-winged Hawk................................................................................................ 31
Rough-legged Hawk ................................................................................................ 32
Golden Eagle........................................................................................................... 32
Bald Eagle ............................................................................................................... 32
Osprey ..................................................................................................................... 33
Merlin ...................................................................................................................... 33
Prairie Falcon ......................................................................................................... 34
Long-eared Owl....................................................................................................... 34
Great Horned Owl................................................................................................... 34
Barred Owl.............................................................................................................. 35
Chapter 2. Hunting Behavior of, and Habitat Use, by Northern Harriers and Short-
eared Owls ....................................................................................................................... 36
Methods........................................................................................................................ 36
Data Analysis .......................................................................................................... 39
Results .......................................................................................................................... 39
Discussion .................................................................................................................... 44
Chapter 3. Nest site selection and reproductive success of Northern Harriers ....... 49
Methods........................................................................................................................ 49
Data Analysis .......................................................................................................... 51
Results .......................................................................................................................... 52
Discussion .................................................................................................................... 57
Chapter 4. Management Implications........................................................................... 67
Literature Cited .............................................................................................................. 69
Appendix A. Tables......................................................................................................... 78
Appendix B. Figures. ...................................................................................................... 90
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Appendix C. Detailed Description of the Road Survey Route. ................................. 112
Appendix D. General Life History Observations....................................................... 115
3
List of Tables
Table 1. Length of the survey route in or adjacent to various units of the Peabody Wildlife Management Area and off the area..................................................................... 79 Table 2. Species of raptors (N = 19) observed on the various units of the Peabody WMA, 2002 - 2003 (X = observed). ............................................................................................. 79 Table 3. Total number of raptors observed during road surveys, 1 January 2002 - 25 July 2003. ................................................................................................................................. 80 Table 4. Total number of raptors observed during road surveys on various units of the Peabody Wildlife Management Area, 2002 – 2003.......................................................... 81 Table 5. Total number of raptors observed during surveys on the Peabody Wildlife Management Area during the winters (January – March) of 2002 (10 surveys) and 2003 (7 surveys)......................................................................................................................... 82 Table 6. Number of Northern Harriers of different sex and age classes observed on the Peabody Wildlife Management Area during the winter (Jan – Mar), 2002 - 2003. ......... 82 Table 7. Proportion of dominant habitats (N = 96 points) found along the survey route through Ohio and Muhlenberg counties, KY, 2002-2003. ............................................... 83 Table 8. Habitats in which raptors were observed during road surveys on the Peabody Wildlife Management Area, 2002 - 2003. ........................................................................ 83 Table 9. Percentage of habitat types used during the non-breeding and breeding season on the Peabody Wildlife Management Area, 2002-2003.................................................. 84 Table 10. Behavior of raptors observed during road surveys on the Peabody Wildlife Management Area, 2002 - 2003........................................................................................ 84 Table 11. Vegetation parameters measured within circular plots in areas used by foraging Short-eared Owls and nesting Northern Harriers, and at randomly-selected unused sites............................................................................................................................................ 85 Table 12. Variables permitting best discrimination between foraging areas of Short-eared Owls and randomly-selected, unused areas on a reclaimed surface mine grassland in west-central Kentucky. ..................................................................................................... 86 Table 13. Number of Northern Harrier nests located on and off the Peabody Wildlife Management Area during the 2003 and 2003 breeding seasons and the fate of those nests............................................................................................................................................ 87
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Table 14. Variables permitting best discrimination between successful and predated nests of Northern Harriers on a reclaimed surface mine grassland in west-central Kentucky. . 88 Table 15. Variables permitting best discrimination between nest sites of Northern Harriers and randomly-selected, unused sites on a reclaimed surface mine grassland in west-central Kentucky. ..................................................................................................... 89 Table 16. Estimated area of potential habitat (open grasslands) for Northern Harriers and the density of Northern Harrier nests (km2) on various units of the Peabody Wildlife Management Area............................................................................................................. 89 Table C-1. Units of the Peabody WMA and odometer readings (starting at Beaver Dam and stopping in the Vogue Unit)..................................................................................... 113 Table C-2. Units of the Peabody WMA and odometer readings (Vogue Unit to Beaver Dam). .............................................................................................................................. 114 Table C-3. Digital orthophotographs (7.5 min, quadrangle quarters) that include portions of the Peabody Wildlife Management Area (KYGEONET 2000). ................................ 114
5
List of Figures
Figure 1. Map of the Peabody Wildlife Management Area in Ohio and Muhlenberg counties, Kentucky.............................................................Error! Bookmark not defined. Figure 2. The survey route through the Peabody Wildlife Management Area and surrounding areas. ..............................................................Error! Bookmark not defined. Figure 3. Mean number of raptors observed per month during road surveys on the Peabody Wildlife Management Area, 2002 – 2003.......................................................... 93 Figure 4. Raptor densities on various units of the Peabody Wildlife Management Area during the winter (January - March), 2002 – 2003 (S = Sinclair, V = Vogue, H/KH = Homestead and Ken Hopewell, RQ = Riverqueen, and G = Gibraltor). Error! Bookmark not defined. Figure 5. Variation in the number of Red-tailed Hawks observed during surveys on the Peabody Wildlife Management Area, 2002 - 2003. ......................................................... 94 Figure 6. Densities of Red-tailed Hawks during the winter (January - March) and summer (June - July) on various units of the Peabody Wildlife Management Area (S = Sinclair, V = Vogue, H/KH = Ken Hopewell and Homestead, RQ = Riverqueen, and G = Gibraltor)........................................................................................................................... 95 Figure 7. Variation in numbers of Northern Harriers observed during road surveys on the Peabody Wildlife Management Area, 2002 - 2003. ......................................................... 96 Figure 8. Densities of Northern Harriers on various units of the Peabody Wildlife Management Area during the winter (January - March), 2002 – 2003 (S = Sinclair, V = Vogue, H/KH = Ken Hopewell, RQ = Riverqueen, and G = Gibraltor). ......................... 96 Figure 9. The location of a communal roost used by Northern Harriers on the SinclairUnit (S1 and S2 intersection) of the Peabody Wildlife Management Area. ........ 97 Figure 10. Variation in numbers of American Kestrels observed during road surveys on the Peabody Wildlife Management Area, 2002 - 2003..................................................... 97 Figure 11. Densities of American Kestrels during the winter (January – March) and summer (June – July) on various units of the Peabody Wildlife Management Area, 2002 – 2003 (S = Sinclair, V = Vogue, H/KH = Ken Hopewell and Homestead, RQ = Riverqueen, and G = Gibraltor). ....................................................................................... 98 Figure 12. Locations of communal roosts of Short-eared Owls on the Sinclair Unit of the Peabody Wildlife Management Area, near S3 food plot areas. ........................................ 99
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Figure 13. Habitats in which Red-tailed Hawks were observed during road surveys conducted during the non-breeding (October - March) and breeding seasons (April - September), 2002 - 2003 (CR = cropland, GL = tall grass, GS = short grass, PAS = pasture, RE = roadside edge, SS = scattered shrub, UNK = unknown, W = woodlot, WE = woodlot edge, and WET = wetland). ........................................................................... 100 Figure 14. Habitats in which Northern Harriers were observed during road surveys conducted during the non-breeding (October - March) and breeding (April - September) seasons, 2002 - 2003 (CR = cropland, GL = tall grass, GS = short grass, RE = roadside edge, SS = scattered shrubs, UNK = unknown, W = woodlot, and WET = wetland). ... 101 Figure 15. Habitats in which American Kestrels were observed during road surveys conducted during the non-breeding (October - March) and breeding (April - September) seasons, 2002 - 2003 (CR = cropland, GL = tall grass, GS = short grass, RE = roadside edge, SS = scattered shrubs, W = woodlot, WE = woodlot edge, and WET = wetland).102 Figure 16. Numbers of Short-eared Owls observed during Paradise Christmas Bird Counts from 1988 through 2003 (based on data from Ferrell 1990-2003)..................... 103 Figure 17. Count area for the Paradise Christmas Bird Count in Muhlenberg, Ohio, Butler, McLean, and Logan counties, Kentucky. ........................................................... 103 Figure 18. Annual variation in number of Red-shouldered Hawks observed during road surveys on the Peabody Wildlife Management Area, 2002 - 2003. ............................... 104 Figure 19. Habitats in which Red-shouldered Hawks (N = 60) were observed during road surveys in the Peabody Wildlife Management Area, 2002 – 2003 (CR = cropland, GL = tall grass, GS = short grass, RE = roadside edge, SS = scattered shrubs, W = woodlot, WE = woodlot edge, and WET = wetland)..................................................................... 104 Figure 20. Habitats in which Rough-legged Hawks (N = 31) were observed during road surveys on the Peabody Wildlife Management Area, 2002 – 2003 (GL = tall grass, GS = short grass, RE = roadside edge, and SS = scattered shrubs). ........................................ 105 Figure 21. Behavior of Rough-legged Hawks (N = 31) observed during road surveys on the Peabody Wildlife Management Area, 2002 – 2003 (DF = direct flight, HF = hunting in flight, HH = hover hunting, PH = perch hunting, PR = perch resting, and S = soaring).......................................................................................................................................... 105 Figure 22. Number of Rough-legged Hawks per party hour observed during the Paradise Christmas Bird Count from 1988 – 2003 (Ferrell 1990-2003). ...................................... 106 Figure 23. Proportion of types of and success rates of attacks (N = 183) used by Northern Harriers on the Peabody Wildlife Management Area (HP = hook pounce, HVP = hover pounce, SP = straight pounce, TD = touchdown, and UNK = unknown). ........ 107
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Figure 24. Proportion of types and success rates of attacks (N = 128) used by Short-eared Owls on the Peabody Wildlife Management Area (HP = hook pounce, HVP = hover pounce, SP = straight pounce, and TD = touchdown). ................................................... 107 Figure 25. Estimated home range of an adult male Northern Harrier on the Ken Hopewell Unit of the Peabody Wildlife Management Area, Ohio County, KY............................. 108 Figure 26. Estimated area of potential habitat (outlined in black) for breeding Northern Harriers during the 2002 and 2003 breeding seasons on the Sinclair Unit of the Peabody Wildlife Management Area, Muhlenberg County, Kentucky (11.9 km2; white circles indicate 2002 nests and black triangles 2003 nests). ...................................................... 109 Figure 27. The stage during nesting when nests of Northern Harriers on the Peabody Wildlife Management Area were lost to predators. ........................................................ 110 Figure 28. Dominant vegetation at nests of Northern Harrier nests (N = 44) on the Peabody Wildlife Management Area, 2002 – 2003 (black = blackberry, catt = cattail, dogb = dogbane, fesc = fescue, indcurr = indian current, ironw = ironweed, ser = sericea, swpe = sweet pea, and swit = switchgrass)..................................................................... 110 Figure 29. Use of exotic and native vegetation by Northern Harriers on the Peabody Wildlife Management Area, 2002 - 2003. ...................................................................... 111 Figure 30. Location of Northern Harrier nests on the Sinclair Unit of the Peabody Wildlife Management Area in 2002 and 2003 (white circles indicate 2002 nests and black triangles 2003 nests). ...................................................................................................... 111
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Introduction Grasslands are among the most threatened habitats in North America
(Jones and Bock 2002), and many grassland bird populations are declining at rates
exceeding those of forest species (Herkert 1994). Two species of grassland raptors,
Short-eared Owls (Asio flammeus) and Northern Harriers (Circus cyaneus), have
exhibited population declines over the past several decades. During the past 35 years,
Short-eared Owls and Northern Harriers have declined at rates averaging 0.7 and 4.4%
per year, respectively, throughout their North American ranges (Sauer et al. 2001). Both
species have been classified as species of national management concern by the U.S. Fish
and Wildlife Service, Short-eared Owls because of current population declines and
Northern Harriers because of their dependence on rare and vulnerable habitats. Although
few investigators have attempted to determine the reasons for this decline, available data
suggest that conversion of grasslands to croplands, disrupted fire regimes, and
fragmentation of remaining grassland habitats have been important factors (Melvin et al.
1989, Serrentino 1992). In Kentucky, Short-eared Owls are classified as endangered, and
Northern Harriers as threatened (KSNPC 2001a).
Prior to the 1800's, and perhaps into the early 1900's, Short-eared Owls and
Northern Harriers probably nested, and certainly wintered, in Kentucky. Audubon (1861)
reported that Northern Harriers frequented the grassy margins of the Mississippi and
lower Ohio Rivers and the 'barrens of Kentucky.' In addition, Wilson (1923) added that
Short-eared Owls were residents of Calloway County. However, since that time many of
Kentucky's native grasslands have been lost. Disrupted fire regimes, conversion to
agriculture, and grazing have reduced the nearly 1 to 1.2 million hectares of Kentucky's
original grasslands and prairie to 500 hectares of small, highly degraded fragments
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(KSNPC 2001b). This loss of grassland habitat contributed to a reduction in the number
of breeding and wintering Short-eared Owls and Northern Harriers in Kentucky.
Although native grassland habitats are scarce, current procedures for reclaiming
surface mines in Kentucky have produced many hectares of open grasslands. In western
Kentucky, coal-mining activities in the Shawnee Hills (or Western Coal Fields) have
converted large areas of upland forest and farmland to grasslands (Palmer-Ball 1996).
For example, the Peabody Wildlife Management Area (WMA) in Ohio and Muhlenberg
counties comprises roughly 25,000 hectares, with most of the area consisting of
'reclaimed' grasslands. The use of reclaimed surface mines by Northern Harriers was
reported in the 1970's in southern Indiana (Palmer-Ball 1996). Consequently, Northern
Harrier nests were found on reclaimed surface mines in Muhlenberg and Ohio counties in
Kentucky in 1989 (Palmer-Ball and Barron 1990). Recent observations of Northern
Harriers and Short-eared Owls indicate that these raptors, and several other species of
raptors, regularly use reclaimed surface mines during the breeding and non-breeding
seasons in Kentucky (Palmer-Ball 1996, Machniak and Elliott 1997) and other locations
in the eastern United States (Rohrbaugh and Yahner 1996, Yahner and Rohrbaugh 1998).
Although previous research has revealed that Short-eared Owls, Northern
Harriers, and other species of raptors use reclaimed surface mines in Kentucky during
both the non-breeding and breeding seasons, little is known about their abundance or the
extent to which these reclaimed areas are used by raptors during the non-breeding and
breeding seasons or about the suitability of these areas as raptor habitat. As such,
Palmer-Ball (1996) noted that 'the extent to which harriers nest on the reclaimed
mines…. is unclear' and, concerning Short-eared Owls, that 'little fieldwork has been
10
undertaken…and it is possible that the species is more widespread than currently
believed.' Further, MacWhirter and Bildstein (1997) suggested that efforts were needed
to better document the breeding range of Northern Harriers, and to monitor populations at
the perimeter of their range. Clearly, more detailed information is needed concerning the
use of reclaimed surface mines by raptors, particularly Short-eared Owls and Northern
Harriers, in western Kentucky. The objectives of this study were to (1) determine the
relative abundance of Short-eared Owls, Northern Harriers, and other raptors using a
reclaimed surface mine in west-central Kentucky (Peabody Wildlife Management Area),
(2) quantify the hunting behavior of Short-eared Owls and Northern Harriers and
characterize the vegetation in areas used by foraging Short-eared Owls and Northern
Harriers during the non-breeding season, and (3) examine the nest-site selection,
provisioning behavior, and reproductive success of breeding Northern Harriers.
Study site
This study took place from 4 January 2002 – 25 July 2003 at the Peabody
Wildlife Management Area (WMA), located in Muhlenberg and Ohio counties of west-
central Kentucky (Figure 1). Peabody WMA includes 25,000 ha of reclaimed coal-mined
land and is divided into six units: the Ken Hopewell and Homestead units in Ohio
County, and the Gibraltor, Sinclair, Riverqueen, and Vogue units in Muhlenberg County.
The Ken Hopewell and Homestead units consist primarily of grasslands and herbaceous
vegetation with scattered woodlots. The Sinclair Unit consists mainly of open grassland
and herbaceous vegetation. The Gibraltor unit consists of open grasslands (adjacent to
private croplands), but remains an active mine and off limits to the public. The
11
Riverqueen and Vogue units include both forested and open habitats. The open areas of
the Peabody WMA consist primarily of non-native vegetation, including sericea
(Lespedeza sp.), fescue (Festuca sp.), crown vetch (Coronilla sp.), and sweet pea
(Lathyrus sp.). Some native plants include, red cedar (Juniperus virginiana), switchgrass
(Panicum sp.), cattail (Typha latifola), dogbane (Apocynum sp.), indian current
(Symphoricarpos orbiculatus), and blackberry (Rubus sp.). A number of ponds are also
present on the Peabody WMA and the area is accessible by several gravel roads.
12
Chapter 1. Populations of Raptors on the Peabody Wildlife Management Area –
Road Surveys
Methods
Populations of Northern Harriers, Short-eared Owls, and other raptors using the
Peabody WMA were monitored using road surveys (Craighead and Craighead 1956,
Fuller and Mosher 1987) during the period from 4 January 2002 through 25 July 2003.
The survey route was 70.7 km long and was selected based on accessibility and visibility
(Figure 2). The route consisted of two sections separated by a section (19.3 km) where
raptors were not counted because of the high volume of traffic (Figure 2). Most of the
survey route was located on or adjacent to the Peabody WMA (42.5 km, or 60.1%;
Figure 1, Table 1, Appendix C). Surveys were conducted at least twice a month, and all
were conducted during the period from 1000 – 1700 h on days with little or no
precipitation and winds less than 20 kph. Successive surveys always began at the
opposite ends of the route.
During surveys, the vehicle was driven at a speed of 20 – 30 kph (Fuller and
Mosher 1987), and I stopped (when possible) when a raptor was sighted. At the
beginning of each survey, the date, weather conditions (temperature, wind speed and
direction, and percent cloud cover), and, if needed, the amount of snow cover or
precipitation was noted. Wind speed was estimated using the Beaufort scale (Lehner
1979). Weather conditions were noted again at the end of the survey. Most surveys were
conducted during the week rather than on weekends (Saturday and Sunday).
13
For each raptor observed, the time, odometer reading, and, if possible, sex and age
were noted. Because identification of female and immature Northern Harriers was not
always possible, some harriers were simply categorized as brown (i.e., either a female or
an immature). In addition, some raptors could only be identified to genus. The distance of
all observed raptors from the road at a 90° angle was estimated. At Vogue and Beaver
Dam (the end and starting points of the survey route), raptors detected at angles other
than 90° were not used in density estimates. Each raptor was given a corresponding
number and, except for initial surveys in January 2002, locations were marked on a map
of the survey route. The habitats in which raptors were observed were also noted.
Specifically, the area within a 50 m radius of where a raptor was observed perched or in
flight was categorized as tall grass (> 50% of the area with grass > 0.5 m high), short
grass (> 50% of the area with grass < 0.5 m high), cropland (areas that have been tilled or
with crop rows), pasture (areas that are grazed by livestock), scattered shrub (shrubs
covering >50% of the area), woodlot (>50% of the area with trees), woodlot edge ( > 5 m
of border of woodlots), wetland (over open water or within 10 m of water's edge), or
roadside edge (< 10 m from a road). In addition, for habitat availability, I drove the
survey route and stopped every 0.8 km (N = 96 points) and determined the dominant
habitat type (> 50 %) at the location. Finally, I categorized the behavior of each raptor as
perched or flying with the following categories: soaring (flying in circles over an area or
gaining altitude), hunting in flight (actively searching for prey, typically looking down,
while flying), direct flight (flapping and moving in one direction), carrying food, perch-
hunting (on a perch and actively searching the ground or horizon for prey), perch-resting
14
(on a perch and preening, not actively searching), vocalization (raptors heard but not
seen) or feeding.
Because Short-eared Owls are largely crepuscular during the winter (Clark 1975),
road surveys conducted during daylight hours produce inaccurate estimates of their
populations. Therefore, an attempt was made to locate all diurnal roost sites used by
these owls on the Peabody WMA and to count all owls present at those roosts. Roost
sites used in previous years (e.g., Machniak and Elliott 1997) were checked, as were
other apparently suitable sites, particularly sites where owls were observed. Observations
of Short-eared Owls from vehicles, prominent hills, and by other observers (e.g., bird-
watching groups and Kentucky Department Fish and Wildlife Resources personnel) were
also used in estimating owl populations. Counts were made during the periods from
January – March 2002 and November – March 2003. In addition to road surveys and owl
counts, any observations of uncommon raptors made during the study (January 2002 –
August 2003) were included in the species list for the Peabody WMA (Table 2).
Data Analysis
Data collected during the road surveys were used to determine the distribution and
relative abundance of raptors on the Peabody WMA throughout the year (Fuller and
Mosher 1987). Percentages and totals of observed species, habitats, and behaviors were
determined for raptors on and off the Peabody WMA. Because the number of surveys
conducted during each month differed in 2002 and 2003, means were used for
comparisons among months.
15
To determine and compare densities of Northern Harriers and other raptors on the
Peabody WMA between years, I used a modified version of the Emlen variable strip
transect count (Emlen 1971, 1977). For each survey and each unit of the Peabody WMA
unit, the area surveyed was calculated (length of transect by width). Transect widths were
calculated using the maximum distance from each side of the road that a raptor was
actually observed. For example, if, during a survey, the most distant raptor observed on
the Sinclair section of the route was 700 m away on one side of the road and 300 m away
on the other side, then, for density calculations, the transect width for that survey and,
specifically, for that section of the survey route, was 1000 m. Larger raptors like Red-
tailed Hawks were more visible and areas used for analyses varied among species. For
each unit, transect areas were then determined by multiplying the calculated transect
width by the length of the route in each unit (Table 1). For area determination, I used the
maximum transect width for each unit (i.e., the maximum distances at which raptors were
observed during all surveys in each unit). For each survey, transect widths were divided
in half and the number of expected individuals was determined. For example, if the
transect width was 200 m, I halved that distance and used 100 m. If 12 harriers were
observed within 100 m of the road, I assumed that there would be 12 additional harriers
in the area between 101 – 200 m from the road when, in fact, I may have only recorded
two more harriers. Therefore, the expected total number of harriers would be 24. I
summed expected numbers from all surveys and units. For each unit, the summed total
of individuals was divided by the total number of expected individuals to generate a
coefficient of detection. The coefficient of detection (COD) represents the proportion of
a population ordinarily detected by an observer. For example, at Sinclair in the winter of
16
2002, I took the number of harriers actually observed (69) and divided that by the number
of 'expected' harriers (127) to obtain a coefficient of 0.54. The summed total number of
individuals (69) was then divided by the transect area (38.8 km2) to obtain a density of
1.78 harriers/km2. Finally, this value was divided by the COD (0.54) to correct for the
unobserved individuals. This value (3.3) was then divided by the number of surveys
during that period (7 surveys in winter of 2002) to generate a density estimate of 0.47
harriers/km2 for the Sinclair Unit during the winter of 2002.
Raptor densities during the winter were estimated based on surveys from 26
January – 31 March 2002 (N = 7 surveys) and 3 January – 17 March 2003 (N = 7). These
dates were used because peak numbers of raptors, particularly Northern Harriers,
occurred during these periods. Further, using these dates provided the opportunity to
compare densities between years. For American Kestrels and Red-tailed Hawks summer
densities, I used surveys conducted from 7 June to 26 July 2002 (N = 6) and 10 June - 25
July 2003 (N = 4).
For habitat availability, dominant habitat types were determined using the
maximum transect width for a location. For example, at Riverqueen, the maximum
transect width was 600 km. I added 50 m (radius of habitat estimation for a raptor) to
both sides of the road. The result was a 700 m diameter circle in which I estimated the
dominant habitat type. Percentages of dominant habitat types were calculated. Chi-
square tests were used to examine possible non-random use of habitats (SAS 1989).
A map of the survey route was digitized using ArcMap 8.1 (ESRI, Redlands, CA)
and 1998 digital orthophotographs obtained from the Kentucky Geography Network
website (KYGEONET 2000a). All data were kept in North American Datum of 1983
17
(NAD 1983), the internationally accepted geodetic reference system (Longley et al.
2001). The coordinate system used was State Plane (feet) 1983 Kentucky South
(Longley et al. 2001). All values presented are means + one standard error.
Results
Survey results
From 4 January 2002 – 25 July 2003, 49 surveys were conducted (163.5 hrs;
2,518.6 km) and 2092 individuals of 15 species were observed (Table 3). For 2002 -
2003, the greatest number of raptors was observed during February, and population
trends were similar from January through July in both years (Figure 3). During both
years, raptor numbers were higher from January through March, then declined in April
and May before increasing again in June and July (Figure 3). The large number of raptors
observed during September 2002 was primarily due to the presence of several large
'kettles' or flocks of Broad-winged Hawks migrating over the Peabody WMA.
Overall, an average of 0.82 raptors/km was observed during the study, with an
average of 0.81 raptors/km on the Peabody WMA. During winter (January - March 2002
and 2003), the mean linear density was 1.17 raptors/km on the Peabody WMA (N = 17
surveys), with similar numbers observed in 2002 (1.19 raptors/km; 10 surveys) and 2003
(1.15 raptors/km; 7 surveys). The mean density of raptors on the Peabody WMA during
the winters of 2002 and 2003 (N = 14 surveys) was 0.33 raptors/km2, with similar
densities in 2002 (N = 7; 0 = 0.36 birds/km2) and 2003 (N = 7, 0 = 0.30 raptors/km2;
Figure 3).
18
More species of raptors were observed on the Sinclair Unit than on any other unit,
both during surveys (N = 14 species) and overall (N = 18; Tables 2 and 4). Similarly,
higher densities of raptors were observed on the Sinclair Unit during the winter than on
other units (Figure 4). Other units where a diversity of raptors was observed included
Riverqueen (N = 10 species on surveys and 14 species overall), Ken Hopewell and
Homestead (N = 9 and 13, respectively), Vogue (N = 9 and 10, respectively), and
Gibraltor (N = 7 and 10, respectively; Tables 2 and 4).
The most frequently observed species of raptor was the Red-tailed Hawk (N =
761, or 36.3% of all raptors; Table 3). Numbers of Red-tailed Hawks were highest
during the fall and winter (October – February), with peak numbers in January and
February (N = 13 surveys; Figure 5, Table 5). Another, smaller peak in number of Red-
tailed Hawks was noted during the breeding season (July; Figure 5). Most Red-tailed
Hawks observed during surveys (N = 439 of 761, or 57.6%) were adults.
Overall (N = 49 surveys), I observed 0.30 Red-tailed Hawks/km along the entire
survey route, and 0.29/km on the Peabody WMA. During the winter (January - March; N
= 17 surveys), 0.45 Red-tailed Hawks/km were observed on the Peabody WMA, with
most being adults (N = 256, or 62.1%). Mean densities of Red-tailed Hawks on the
Peabody WMA during the winter (N = 14 surveys) were similar during the winters of
2002 (0.17/km2) and 2003 (0.13/km2; Figure 6). Densities of Red-tailed Hawks during
the two winters were similar for most units, with the exception of a decline in density in
2003 on the Gibraltor Unit (Figure 6).
The mean density of Red-tailed Hawks on the Peabody WMA during the summer
(June - July) was higher in 2002 (0.24/km2) than 2003 (0.05/km2; Figure 5). For both
19
summers combined, the mean linear density of Red-tailed Hawks was 0.18/km. Fourteen
immature Red-tailed Hawks were observed on the Peabody WMA during both summers
combined.
Northern Harriers were the second most common raptor observed during road
surveys (N = 504 of 2092, or 24.1%; Table 3). Harriers were observed more frequently
on the Peabody WMA (N = 484 of 504, or 96%), particularly on the Sinclair Unit (N =
219 of 504, or 43.4%), than off the Peabody WMA (N = 20, or 3.9%; Table 4). Numbers
of Northern Harriers were highest during the fall and winter (October – March; Figure 7).
Peak numbers of Northern Harriers were observed in February 2002 (N = 4 surveys) and
March 2003, respectively (N = 2 surveys; Figure 7 and Table 5). For both winters
combined, most harriers identified were adults (N = 160 of 329, or 48.6%), with adult
males (N = 92 of 160, or 57.5%) observed more often than adult females (N = 68 of 160,
or 42.5%; Table 6).
Overall (N = 49 surveys), I observed an average of 0.19 harriers/km along the
survey route, with an average of 0.22/km observed on the Peabody WMA. During the
winter (January - March; N = 17 surveys), an average of 0.45 harriers/km were observed
on the Peabody WMA (0.48/km in 2002 and 0.42/km in 2003, respectively). The mean
density of Northern Harriers on the Peabody WMA during the winter (N = 14 surveys)
was 0.20/km2 (Figure 8).
Among units, the highest densities of harriers were observed on the Sinclair Unit
in 2002 (N = 0.46 harriers/km2) and on the Gibraltor Unit in 2003 (N = 0.31 harriers/km2;
Figure 8). Densities of Northern Harriers on the Vogue Unit were higher in 2003
(0.14/km2) than in 2002 (0.02/km2; Figure 8). Although harrier densities and numbers
20
fluctuated on the Sinclair Unit during both winters, maximum numbers of harriers at the
communal roost were similar (Figure 9). The number of harriers at the communal roost
was highest in March in both 2002 (N = 25) and 2003 (N = 23).
American Kestrels were the third most common raptor observed during the
surveys (N = 487, or 23.3%; Table 3). Kestrel numbers varied throughout the study with
peak numbers observed during July (N = 5 surveys; 0 = 17.8 ± 10.8 birds) and numbers
also relatively high during the fall and winter (September – February; Figure 10). Kestrel
numbers were generally lower in 2003 than 2002 (Figure 10). I observed more male
kestrels (N = 233, or 47.8%) than female kestrels (N = 99, or 20.3%).
Overall (N = 49 surveys), I observed an average of 0.19 kestrels/km along the
survey route, with an average of 0.16 kestrels/km on the Peabody WMA. During the
winters of 2002 and 2003 (N = 17 surveys), an average of 0.15 kestrels/km were
observed on the Peabody WMA. The mean densities of American Kestrels during the
winter (N = 14) were similar for 2002 and 2003 (0.10 and 0.11 birds/km2, respectively;
Figure 11). Densities of American Kestrels on the Peabody WMA were also similar
during the summers (June – July) of 2002 and 2003 (0.28 and 0.23 birds/km2,
respectively; Figure 11).
Although only two Short-eared Owls were observed during surveys, additional
attempts to locate owls on the Peabody WMA were made. Based on those efforts, I
estimated that 27 Short-eared Owls were present on the Peabody WMA (excluding the
Gibraltor Unit) in 2002, while 28 were present in 2003. Short-eared Owls were observed
only on the Sinclair Unit during 2002, with a maximum count of 27 individuals in
February. No owls were observed on the Peabody WMA from 13 April - 30 November
21
2002. The location of a communal roost of Short-eared Owls was discovered on the
Sinclair Unit on 13 November 2002 (Figure 12), and counts at the roost revealed 18
individuals present in January. This roost subsequently moved about 150 m after
discovery (Figure 12). In addition, seven Short-eared Owls were observed on the Ken
Hopewell Unit, two on the Riverqueen Unit (25 January), and one on the Vogue Unit (17
February).
Habitat use
Woodlot and tall grass habitats were the dominant habitats along the survey route
(Table 7). Raptor presence in habitats along the survey route was non-random (χ2 =
175.3, df = 8, P < 0.0001), with raptors observed most frequently in areas with tall grass
(N = 1179 of 2092 raptor observations, or 56.4%; Table 8). For all raptors combined,
habitat use exhibited seasonal variation (χ2 = 79.1, df = 8, P < 0.0001), with greater use of
woodlots during the breeding (April - September; 118 of 704 observations, or 16.8%)
than during the non-breeding (Table 9: October - March; 102 of 1384, or 7.4%). Use of
roadside edge and woodlot edge habitats was also greater during the non-breeding season
(Table 9).
Among individual species, habitat use by Red-tailed Hawks was also non-random
(χ2 = 67.4, df = 8, P < 0.0001), with these hawks observed most often in tall grass habitats
(Figure 13). Other habitats used frequently by Red-tailed Hawks were roadside edge and
woodlots (Figure 13). Habitat use by Red-tailed Hawks did vary seasonally (χ2 = 19.7, df
= 8, P = 0.011), with fewer observed in woodlot edge habitats during the breeding season.
22
Northern Harriers were also observed significantly more often in tall grass
habitats (χ2 = 251.7, df = 7, P < 0.0001; 80.9% of all observations), with other habitats
used infrequently (Figure 14). Although based on only 71 observations during the
breeding season, habitat use by harriers did differ with season (χ2 = 15.3, df = 6, P =
0.018). More harriers were observed in roadside edge habitat during the non-breeding
period (34 of 431 observations, or 7.9%) than during the breeding period (1 of 71
observations, or 1.4%).
American Kestrels were also observed significantly more often in tall grass
habitats (χ2 = 268.3, df = 8, P < 0.0001; Figure 15), but were also regularly observed in
short grass and roadside edge habitats (Figure 15). Kestrels exhibited seasonal variation
in habitat use (χ2 = 39.9, df = 7, P < 0.0001), with more kestrels observed in short grass
(50 of 261 observations, or 19.1%) and roadside edge (75 observations, or 28.7%)
habitats during the non-breeding season and in tall grass habitats (155 of 226
observations, or 68.6%) during the breeding season.
Behavior
Overall, raptors observed during road surveys were most often engaged in perch
hunting (N = 767, or 36.7%) and soaring (N = 491, or 23.5%; Table 10). More raptors
were observed hunting (perch hunting, hunting in flight, or hover hunting) during the
non-breeding season (837 of 1388 observations, or 60.3%) than during the breeding
season (257 of 704 observations, or 36.5%). In addition, more raptors were observed in
direct flight (200 of 704 observations, or 28.4%) during the breeding season (April-
23
September) than during the non-breeding season (October - March; 172 of 1388
observations, or 12.4%).
Red-tailed Hawks were most frequently observed perch hunting (N = 350, or
45.9% of all observations) and soaring (34.8%). The most common behaviors of
Northern Harriers observed during road surveys on the Peabody WMA were hunting in
flight (N = 246, or 48.8% of all observations) and soaring (29.9%). Most American
Kestrels observed during road surveys were engaged in perch hunting (N = 368, or 75.6%
of all observations).
Discussion
Survey results
My survey results revealed that the density of raptors on the Peabody WMA
during the winter was 1.17 raptors/km or 0.33/km2. Sferra (1982) reported much lower
numbers of wintering raptors in Madison County, Kentucky, with a mean linear density
of 0.24 raptors/km. However, Andres (1994) examined winter densities of raptors in
western Clark County, Kentucky, and reported a mean density of 1.35 raptors/km2. The
mean density of wintering raptors at a study site in Ohio was 1.28 raptors/km2 over a
four-year period (Bildstein 1987). Differences in raptor densities in these studies were
largely due to differences in the numbers of the most commonly observed raptors, Red-
tailed Hawks and American Kestrels. For example, the highest density of Red-tailed
Hawks in my study was 0.17/km2 during the winter of 2002. In contrast, Andres (1994)
reported a density of 0.62 Red-tailed Hawks/km2 during the winter in Clark County,
Kentucky. The density of wintering American Kestrels on the Peabody WMA during my
24
study (0.11/km2) was much lower than that reported in Ohio (0.32 kestrels/km2; Bildstein
1987). Although Red-tailed Hawks and American Kestrels often forage in open habitats,
both species are primarily sit-and-wait predators typically found in areas with scattered
perches (Preston and Beane 1993, Smallwood and Bird 2002). In addition, Red-tailed
Hawks typically roost in ‘groups of trees’ (Preston and Beane 1993), while American
Kestrels roost ‘in cavities or dense vegetation’ (Smallwood and Bird 2002). Thus, areas
with large expanses of open habitat and fewer or more scattered groups of trees, like the
Peabody WMA, will likely have lower populations of these species than areas with more
wooded habitat.
The density of Northern Harriers on the Peabody WMA during the winter was
0.45/km or 0.20 birds/km2. Few investigators have reported densities of wintering
harriers. Bildstein (1987) reported a density of 0.46 Northern Harriers/km2 in Ohio
(Bildstein 1987). While higher than my overall density, I found a comparable density of
harriers on the Sinclair Unit in 2002 (0.46 harriers/km2). Other investigators have
reported lower densities of wintering harriers. For example, Craighead and Craighead
(1956) reported 0.13 harriers/km2 in Michigan, while Sferra (1982) reported a density of
0.005 harriers/km2 during the winter in Madison County, Kentucky. At other locations in
Kentucky, small numbers of Northern Harriers are typically reported during midwinter or
Christmas bird counts. Sauer et al. (1997) indicated that the number of Northern Harriers
in Kentucky ranged from 4 - 10 individuals per Christmas Bird Count. The high numbers
of Northern Harriers on the Peabody WMA relative to other locations within the species
range suggests that the reclaimed surface mines in general, and the Peabody WMA
specifically, provide suitable habitat for these grassland raptors. Similarly, Rohrbaugh
25
and Yahner (1996) found that Northern Harriers were five times more abundant on
reclaimed surface mine grasslands in Pennsylvania than in agricultural areas, and
suggested that, if managed properly, grasslands on reclaimed surface mines could provide
important habitat for harriers. Reclaimed strip mines also provide suitable habitat for
Northern Harriers in Ohio (Peterjohn and Rice 1991).
The distribution and abundance of Short-eared Owls during the winter are poorly
known, but, based on Christmas bird count data, populations in most areas of the United
States appear to be low (Sauer 1997) and, in some states (Illinois and Iowa), declining
(McKay and Stravers 2001). Numbers of Short-eared Owls observed on the Peabody
WMA during the winter are among highest reported in the United States. My
observations suggested that at least 27 Short-eared Owls were on the Peabody WMA
during the winter of 2002, and 28 were on the area in 2003. However, additional owls
may have been present during both years. For example, observers participating in the
Paradise Christmas Bird Count in 2002 reported that 37 Short-eared Owls were found on
the Peabody WMA (Ferrell 2002; Figures 16 and 17). Numbers of Short-eared Owls
reported for Christmas Bird Counts at other locations in the United States have been
lower than those reported at Paradise. For example, the highest number reported for all
other Christmas Bird Counts in 2002 was 19 Short-eared Owls at the Killdover Plains
Wildlife Area in Ohio (NAS 2002). For the 2003 bird counts, the highest number
reported was 29 Short-eared Owls at the Hulah Reservoir in Oklahoma (NAS 2003).
Because much apparently suitable habitat throughout its range is not occupied, the
relatively high number of wintering Short-eared Owls on the Peabody WMA suggests
that, beyond simply providing suitable habitat, the area likely also supports good prey
26
populations (e.g., Machniak and Elliott 1997). Holt and Leasure (1993) noted that ‘levels
of prey’ were an important factor in habitat selection by Short-eared Owls.
Results from my study revealed an apparent decline in raptor populations on the
Peabody WMA from 2002 to 2003. Although I did not measure prey populations, prey
availability rather than absolute densities, may be the best indicator of raptor density and
habitat selection during the non-breeding season (Baker and Brooks 1981). Prey
availability may have either decreased in 2003 or simply changed, with the distribution of
prey differing between years. For example, counts of Northern Harriers at communal
roosts at the Sinclair Unit during the winters of 2002 and 2003 were similar, but numbers
and densities were lower in 2003. Such results suggest that Northern Harriers may have
traveled greater distances from the communal roost to foraging locations in 2003 and,
thus were less likely to be observed during road surveys. In addition, numbers of Short-
eared Owls declined on the Sinclair Unit from 2002 to 2003, but numbers increased in
2003 on other units. The numbers and densities of raptors on other units, such as
Riverqueen, also varied between years, further suggesting possible variation in prey
availability.
Weather can also influence winter populations of raptors (Brown and Amadon
1968). I found that the mean temperature during surveys conducted during the winter of
2003 was lower than for 2002. In addition, the mean winter (December - February)
temperature for the central United States (including Kentucky, West Virginia, Indiana,
Missouri, Ohio, Tennessee, and Illinois) was lower in 2003 (0 = 30.1° F) than in 2002 (0
= 37.3° F; NOAA 2003). Lower temperatures in Kentucky and north of Kentucky may
have caused raptors to moved further south during the winter of 2003. Thus, changes in
27
raptor populations on the Peabody WMA between years and among units of the Peabody
WMA may have been the result of changes in prey availability, weather, or both.
Habitat Use and Foraging Behavior
Observations of habitat types used by raptors during my study revealed that most
were observed in tall grass habitat. The frequent occurrence of foraging raptors in tall
grass habitat suggests that such areas may support higher populations of prey than other
habitats on the Peabody WMA. Although information concerning the area and habitat
sampled was not provided, Machniak and Elliott (1997) reported higher densities of small
mammals on the Peabody WMA than on the nearby National Guard Training Site.
Seasonal differences in habitat use were noted for American Kestrels and Red-
tailed Hawks. For Red-tailed Hawks, use of woodlot edge habitat declined in the
breeding season. One possible explanation for this is that visibility due to 'leaf out' made
detecting Red-tailed Hawks in edge habitat more difficult during the breeding season.
For American Kestrels, use of short grass and roadside edge habitats increased during the
breeding season. The presence of family groups, which included young, inexperienced
kestrels in July, may have contributed to this difference in habitat use. A combination of
greater availability of perches along roads (utility poles and lines) along with increased
prey vulnerability in the short grass habitats found in these areas may have made these
habitats more suitable for kestrels, particularly young kestrels.
Hunting or foraging was the most common behavior of raptors observed on the
Peabody WMA during road surveys. During the winter, raptors may spend more time
foraging due to a combination of reduced prey availability and increased energetic (i.e.,
28
thermoregulatory) needs. Soaring was also a common behavior observed during road
surveys. My surveys were conducted during the afternoon, typically the warmest part of
the day. Thus, raptors used thermals generated by the afternoon sun to facilitate soaring.
Preston and Beane (1993) suggested that soaring may serve a variety of functions,
including migration, courtship, territorial advertisement, exploration, foraging, and
thermoregulation (Preston and Beane 1993). During the breeding season, raptors
observed during my study were more often observed making direct flights, with some of
these flight likely representing adults flying to and from nest sites.
Some sex- and age-related differences in behavior were observed during my
study. For example, juvenile harriers were observed hunting more often than adults
during the non-breeding season. Young harriers and other young raptors may be less
efficient hunters (Toland 1986, Bildstein 1987) and may also be limited by adults to
lower quality habitats. As a result, young raptors may need to spend more time foraging
than adults.
Only male American Kestrels were observed hover hunting during my study. In
contrast, male and female kestrels in Florida were equally likely to use hover hunting
(Smallwood 1987). Because male kestrels are smaller than female kestrels, males may
use less energy when hover hunting than females (Bostrom 2003).
Other Raptors Observed During Road Surveys
Mississippi Kite
Mississippi Kites were observed during the spring and summer on the Sinclair
Unit of the Peabody WMA. Four individuals were observed on 17 June 2002 on the
29
Sinclair Unit. In 2003, only single individuals were observed on the Sinclair Unit,
including one during a survey on 10 June 2003. On several occasions, Mississippi Kites
were observed feeding on dragonflies. Although I did not locate any Mississippi Kite
nests, the occurrence of these kites on the Peabody WMA during the breeding season
suggest that breeding pairs may have been present.
Swallow-tailed Kite
A post-breeding adult Swallow-tailed Kited was observed from 12 – 31 August
2003 on the Sinclair Unit. Although now rarely observed in the state, Kentucky is within
the historical range of this species (Palmer-Ball 1996). Suitable habitat for Swallow-
tailed Kites appears to be available on the Peabody WMA, and transient individuals will
likely be observed in the future.
Sharp-shinned Hawk
Sharp-shinned Hawks were observed primarily on the Peabody WMA (Table 4)
during the fall and winter. My survey results likely underestimated the numbers of these
hawks on the area because of their preference for forested areas.
Cooper’s Hawk
The Cooper’s Hawk was the most frequently observed accipiter during my study.
These hawks were observed in a variety of habitats and on several units of the Peabody
WMA, with the greatest number observed on the Riverqueen Unit (N = 8; Table 4).
Apparent courtship flights and individuals carrying prey were observed on the
30
Riverqueen Unit in May and July 2002 and on the Ken Hopewell Unit in May 2003,
suggesting the possible presence of one or more breeding pairs.
Red-shouldered Hawk
Numbers of Red-shouldered Hawks on the Peabody WMA were highest in
February (Figure 18), suggesting that most individuals present were winter visitors rather
than residents. However, an apparent courtship flight by a Red-shouldered Hawk was
observed on 6 March 2002 on the Riverqueen Unit and numbers did increase in July
(Figure 19). These observations suggest the presence of at least a small breeding
population of Red-shouldered Hawks on the Peabody WMA. Red-shouldered Hawks
were most frequently observed in woodlots (N = 25, or 41.6% of observations; Figure
21).
Broad-winged Hawk
Migrating Broad-winged Hawks were observed on the Peabody WMA during
both the spring and fall. Specifically, 109 Broad-winged Hawks were observed on 13
April 2002, with 94 observed on the Sinclair Unit and 15 on the Vogue Unit. On 26
April 2003, 41 Broad-winged Hawk were observed in flight over the Vogue Unit. On 21
September 2003, three separate kettles consisting of a total of 131 individuals were
observed, and one kettle originated from an unidentified roost location on the Ken
Hopewell Unit. Although all observations suggested migrating birds, the Peabody WMA
may serve as an important stopover site for this migrant.
31
Rough-legged Hawk
Rough-legged Hawks (both morphs) were observed during each winter of the
study on the Sinclair, Homestead, and Ken Hopewell units. Most of these hawks were
observed in tall grass habitats (N = 24 of 31 observations, or 77.4%; Figure 20), and most
were observed soaring (N = 10 of 31, or 32.2%) and perch hunting (N = 9, or 29%;
Figure 23). Populations of Rough-legged Hawks in the Paradise area appear to have
declined over the past 15 years (Ferrell 1990 - 2003; Figure 24). This decline may be due
to changes in habitat availability or suitability, increased human activity, climate change,
or a combination of these factors.
Golden Eagle
One immature Golden Eagle was observed on the Riverqueen Unit during a
survey on 30 January 2003 (near the RQ 1 and RQ Haul Road intersection). This
individual may have been feeding on a dead opossum (Didelphis virginiana).
Bald Eagle
Two Bald Eagles were observed during road surveys, and 10 additional Bald
Eagles were observed on the Peabody WMA during other phases of this study. The
abundance of ponds and lakes on the Peabody WMA, particularly on the Sinclair Unit,
likely provides suitable foraging habitat for these eagles. The discovery of a nesting pair
in Muhlenberg County in 2003, along with three observations of immature eagles
(possible the same bird observed three times) on the Homestead Unit (22 and 29 May and
14 June), suggests the possibility of future breeding pairs on or near the Peabody WMA.
32
Osprey
Ospreys were observed during road surveys on the Peabody WMA from late
through the fall. In addition, one nest was located on in a short-grass habitat at Paradise.
This nest and another nest located near the Green River adjacent to the Ken Hopewell
Unit were monitored regularly. The Paradise nest was successful (fledged at least one)
both years. The Ken Hopewell Unit nest was damaged during a storm, but the adults
repaired the nest and nested successfully (three young fledged) in 2003. The numerous
ponds and lakes on and near the Peabody WMA likely provide ample foraging locations
for Ospreys.
Merlin
During road surveys in 2002, Merlins were observed on the Riverqueen (N = 3),
Vogue (N = 2), and Sinclair (N = 1) units. Also in 2002, four Merlins (2 males and 2
females) regularly arrived on the Riverqueen Unit (RQ2 - RQ1 area) at dusk and perched
on utility poles. Then, just before dark, they flew to night roosts [at least one roosted in a
Virginia pine (Pinus virginia)]. I also located a ‘plucking perch’ on 17 January 2002 on
the Riverqueen Unit. Prey remains below the perch indicated that a male Merlin had
been feeding on Red-winged Blackbirds (Agelaius phoeniceus). Early in the morning on
26 January 2002, this Merlin was observed pursuing flocks of blackbirds.
During 2003, no Merlins were observed during road surveys. However, at least
one bird was observed on the Riverqueen Unit on 2 November 2003, and one pair was
observed several times (4 - 6 January 2003) and may have spent the winter on the
Homestead Unit. Another bird was reported on the Sinclair Unit on 1 March 2003
33
(Ferrell 2003a). Finally, an apparent migrant Merlin was observed on 26 April 2003 on
the Sinclair Unit. My observations suggest that Merlins migrate through the area and
some individuals may winter on the Peabody WMA, perhaps attracted by the large flocks
of icterids that winter on and near the area.
Prairie Falcon
This extremely rare visitor to Kentucky was not observed during the survey, but
was observed during the study period. One adult was observed and photographed on 15
January 2002 on the Sinclair Unit. At dusk, this falcon flew into a red cedar to
apparently roost for the night, and was not observed again.
Long-eared Owl
Previous investigators have documented the presence of wintering Long-eared
Owls on the Peabody WMA (Machniak and Elliott 1997). On 8 January 2002, four
Long-eared Owls were flushed from their roosts in a stand of Virginia pines on the
Riverqueen Unit. Two more owls were flushed from roosts in the same area on 14
January 2002. No Long-eared Owls were observed on the Peabody WMA in 2003. As
long as the habitat remains unchanged, small numbers of Long-eared Owls will likely
continue to spend the winter on the Peabody WMA.
Great Horned Owl
Three Great Horned Owls were observed during road surveys on the Peabody
WMA. All observations were either of a roosting owl or of owls flushed from trees near
34
the road. In addition to observations during road surveys, Great Horned Owls were
observed almost daily during the winter. On 26 January 2002, 20 Northern Harriers and
two Short-eared Owls were observed mobbing a perched Great Horned Owl on the
Sinclair Unit. In 2003, I located a Great Horned Owl nest (in an old Red-tailed Hawk
nest) on the Sinclair Unit, but the nest failed. Great Horned Owls are common predators
on the Peabody WMA, and likely represent a threat to many other species of raptors that
occur on the area.
Barred Owl
No Barred Owls were observed during road surveys on the Peabody WMA.
However, one individual was observed on 14 February 2002 near the perimeter of the
Riverqueen Unit, and another was heard vocalizing on the Sinclair Unit on 7 July 2002.
Although no other Barred Owls were observed during the study, suitable habitat is
available for these owls on the Peabody WMA and they are likely more common than my
observations suggest.
35
Chapter 2. Hunting Behavior of, and Habitat Use, by Northern Harriers and Short-
eared Owls
Methods
The hunting behavior of Northern Harriers and Short-eared Owls on the Peabody
WMA was observed during the period from 1 January 2002 – 1 May 2002. Observations
were made 2 - 3 times a week. Observations of harriers were made throughout the day on
the Sinclair, Homestead, and Vogue units. Short-eared Owls were only observed on the
Sinclair Unit, typically beginning 2 - 4 h before sunset and continuing until it was too
dark.
Once in the study area, observations began as soon as either a harrier or owl was
located, and continued until that focal individual was lost from view. Observations then
continued when another individual was located. Hunting harriers and owls were
observed from distances ranging from 5 - 300 m. Spotting scopes were used for some
long distance observations (> 200 m). If a ‘new’ individual at a particular location was
thought to be one observed previously on that day, I either waited until another bird came
into view or moved to a different location before resuming observations. All
observations were made from a vehicle or from the top of an elevated area.
During each observation of a Northern Harrier or Short-eared Owl, I noted the (1)
amount of time spent perched, hunting in flight, soaring, hovering (Clark 1975), carrying
prey, and feeding, (2) the method of hunting, (3) height above ground when hunting, (4)
distance flown between successive pounces or touchdowns, (5) the number of pounces
and whether pounces were successful, and (6), if possible, the prey species captured.
36
Hunting methods were categorized as hook pounces, hover pounces, straight pounces,
touchdowns, or bird chases (Bildstein 1987). In addition, flights were categorized as
quartering, transect flights, border following, soaring, or direct flights (Bildstein 1987).
If a focal bird remained on a perch for more than 0.5 h, the observation period was ended.
Beginning in November 2003, the Peabody WMA was searched for foraging
Short-eared Owls in an attempt to identify high-use areas. Based on those observations, I
identified areas (N = 10) most frequently used by hunting Short-eared Owls. In those
areas, a 50-m circular plot was established, with the plot center being a spot where an owl
had initiated one or more attacks. Vegetation within these plots and at seven randomly-
selected, apparently unused sites was sampling following methods described by James
and Shugart (1970). Random sites were selected by randomly picking two digits from a
random number table. Numbered grid maps of the Peabody WMA were then used to
determine the location of random sites. At 10-m intervals along transects radiating from a
plot center in the four cardinals directions, I measured: (1) foliage cover at vertical
intervals of <0.5 m, 0.5 – 1 m, and 1 – 2 m, (2) percent cover of plants (grass, herbaceous
vegetation, shrubs, or trees) and bare ground, (3) litter depth, (4) vegetation height, and
(5) lateral cover at vertical intervals of < 0.5 m, 0.5 – 1 m, 1 – 2 m. Lateral cover was
recorded at a distance of 10 m (Table 11). From the center of each plot, the distance to
the closest shrub, tree, and edge (boundary zone between fields and woodlots) was also
measured. Approximate distances from plot centers to the nearest gravel road, state
(paved) road, and permanent water were determined using ArcMap 8.1. State roads were
downloaded from a website (KYGEONET 2000b). State roads were from historical
records dating back to 1929 and were outdated and inaccurate in some areas near the
37
Peabody WMA. These inaccurate segments were correctly aligned with roads on 1998
digital orthophotographs (KYGEONET 2000a). The Peabody WMA roads and
permanent water features were digitized from 1998 digital orthophotographs
(KYGEONET 2000a).
From November 2002 – March 2003, I attempted to capture Northern Harriers
and Short-eared Owls. Mist nets with a model of a Great Horned Owl placed nearby
were initially used in an attempt to capture ‘mobbing’ harriers or owls, but despite
several attempts, no harriers or Short-eared Owls were captured. However, using a bal-
chatri trap (made from chicken-wire) baited with European Starlings (Sturnis vulgaris), I
was able to capture one adult male Northern Harrier on 28 February 2003. The harrier
was fitted with a numbered, aluminum band and transmitter (Holohil Systems Ltd., Carp,
Ontario, Canada). The transmitter (5 gm) was attached using a tail mount (at the base of
three central rectrices), and the harrier was subsequently tracked using a receiver
(Telonics Inc., Mesa, AZ) with 2-element directional antenna. The harrier was
subsequently tracked (N = 7 locations) until the bird disappeared on 18 March 2003. All
locations were determined by homing and the using a GPS unit . The area used
delineated (minimum convex polygon) using ArcMap 8.1. Area estimates of polygons
were obtained using a script from the ESRI website (ESRI 2003). This script
automatically calculates the polygon area (digitized area) in square feet, which was then
converted to square kilometers.
38
Data Analysis
Because individuals were not marked and could not be identified and because
many individuals (based on variation in numbers of Northern Harriers and Short-eared
Owls present on the Peabody WMA over time) were likely transients, I assumed, for
purposes of statistical analysis, that all observations of foraging harriers and Short-eared
Owls made during different observation periods were independent (i.e., different
individuals). Possible differences between Short-eared Owls and Northern Harriers in
foraging behavior were examined using chi-square tests for categorical variables and
Wilcoxon tests for continuous variables (SAS 1989). Possible differences in the foraging
behavior of male and female Northern Harriers, as well as the foraging behavior of adult
and subadult Northern Harriers were also examined using chi-square and Wilcoxon tests
(SAS 1989). The possible effects of wind speed on the foraging heights of Short-eared
Owls and Northern Harriers, respectively, were examined using Kruskal-Wallis tests
(SAS 1989). Finally, the characteristics of foraging areas used by Short-eared Owls and
randomly-selected, unused sites were compared using multivariate analysis of variance
(MANOVA). Stepwise discriminant analysis was then used to identify variables that best
discriminated between sites (SAS 1989). Values are presented as means + one standard
error.
Results
Northern Harriers used five types of hunting flights, with quartering flights (N =
222 of 344, or 64.5%) and transect flights (N = 114 of 344, or 33.1%) used most often.
39
Harriers rarely hunted by soaring (N = 3) or by using border flights (N = 2) and direct
flights (N = 3). Short-eared Owls used primarily quartering flights (N = 175 of 182, or
96.2%). Other types of hunting flights used by Short-eared Owls included soaring (N =
3), transect flights (N = 3), and direct flights (N = 1). Male and female Northern Harriers
differed in types of flights used when foraging (χ2 = 9.58, df = 1, P = 0.002), with
females using quartering flights (138 of 187, or 73.8%) more often than transect flights
(49 of 187, or 26.2%) and males using quartering flights (43 of 79, or 54.4%) and
transect flights (36 of 79, or 45.6%) to similar degrees.
Northern Harriers foraged significantly closer to the ground than Short-eared
Owls (z = 2.70, P < 0.0069), with a mean height of 1.70 + 0.07 m (N = 288) for harriers
and 1.81 + 0.11 (N = 124) for Short-eared Owls. Flight type (quartering flights vs.
transect flights) did not influence the height of foraging Northern Harriers (z = 0.7, P =
0.48). Male and female Northern Harriers exhibited a significant difference in mean
foraging height (z = 2.53, P = 0.0115), with females foraging at a mean height of 1.55 +
0.08 m (N = 161) and males at a mean height of 1.81 + 0.13 m (N = 70). Differences
between Northern Harriers and Short-eared Owls in mean distance flown between
successive pounces or touchdowns approached significance (z = 1.65, P = 0.099), with
harriers flying a mean distance of 73.99 + 7.75 m (N = 342 observations) between
pounces or touchdowns and Short-eared Owls flying a mean distance of 58.25 + 6.99 m
(N = 243 observations).
Foraging height varied with wind speed for both male (H = 18.12, df = 3, P =
0.0004) and female (H = 27.61, df = 3, P < 0.0001) Northern Harriers, but no clear trends
were apparent. No observations were made of either male or female harriers foraging at a
40
wind velocity of 0 on the Beaufort scale. At wind velocities of 1, 2, 3 and 4 on the
Beaufort scale, mean foraging heights of male harriers were 1.77 + 0.30 m (N = 35), 2.19
+ 0.17 m (N = 26), 1.84 + 0.14 m (N = 50), and 1.84 + 0.53 m (N = 13), respectively.
For female Northern Harriers, mean foraging heights at wind velocities of 1, 2, 3 and 4
on the Beaufort scale were 1.62 + 0.19 m (N = 65), 1.92 + 0.12 m (N = 61), 1.39 + 0.08
m (N = 75), and 2.09 + 0.45 m (N = 17), respectively. For male and female harriers
combined, the mean distance flown between successive pounces or touchdowns also
varied significantly with wind speed (H = 18.03, df = 3, P = 0.0004), but, again, no trend
was apparent. Mean distances were longer at wind speeds of 1 (N = 95) and 4 (N = 22)
on the Beaufort scale (0 = 104.82 + 20.12 m and 96.59 + 18.40 m, respectively) and
shorter at wind speeds of 2 (N = 80) and 3 (N = 142) on the Beaufort scale (0 = 44.05 +
4.24 m and 65.84 + 12.08 m, respectively).
Wind speed also influenced the foraging heights of Short-eared Owls (H = 36.72,
df = 3, P < 0.0001). At a wind velocity of 0 on the Beaufort scale, their mean foraging
height was 1.20 + 0.13 m (N = 10). At wind velocities of 1, 2 and 3 on the Beaufort scale,
mean foraging heights for Short-eared Owls were 1.33 + 0.14 m (N = 12), 2.01 + 0.12 m
(N = 78), and 1.30 + 0.10 m (N = 23), respectively. Short-eared Owls were observed
foraging at a wind velocity of 4 on the Beaufort scale on just one occasion. Wind velocity
did not influence the mean distance flown by Short-eared Owls between successive
pounces or touchdowns (H = 6.12, df = 3, P = 0.11).
Observations of hunting Northern Harriers (N = 792 observations during 35.3 h of
observation) revealed that 7% of attacks (N = 183 attacks) were successful. In contrast,
10.9% (14 of 128 attacks) of all attacks by Short-eared Owls (N = 505 observations
41
during 16.6 h) were successful. Both species used straight pounces (N = 63, or 34% for
Northern Harriers, and N = 43, or 32.5% for Short-eared Owls; Figures 23 and 24) more
often than other types of attacks. Hook and hover pounces were more successful for
Short-eared Owls (6 of 14 successful attacks, or 42.8%), while hover pounces (6 of 33
successful attacks, or 3%) were more successful for Northern Harriers. No bird chases
were recorded for either species.
When attacking prey, both Northern Harriers and Short-eared Owls used straight
pounces, hook pounces, and hover pounces most frequently (Figures 23 and 24). Attack
success was low for both species, with success rates of 7% (N = 13 of 183 attacks) for
Northern Harriers and 10.9% (N = 14 of 128 attacks) for Short-eared Owls. I found no
difference between male and female Northern Harriers in success rates (χ2 = 0.12, df = 1,
P = 0.73), with female attacks successful 8.5% (8 of 94) of the time and attacks by males
successful 6.8% (3 of 44) of the time. Although no difference was found between attack
success rates of adult and subadult Northern Harriers (χ2 = 2.17, df = 1, P = 0.14), all
observed attacks by subadults (N = 25) were unsuccessful.
The vegetation at locations where attacks were made was identified when possible
(N = 51 for Northern Harriers and N = 41 for Short-eared Owls). For both species, most
attacks were initiated in areas dominated by sericea (N = 32 of 51, or 62.7% for harriers
and N = 22 of 41, or 53.6% for Short-eared Owls). For both Northern Harriers (N = 18 of
51, or 35.2%) and Short-eared Owls (N = 17 of 41, or 41.4 %), most of the remaining
attacks were initiated in areas dominated by fescue. Female Northern Harriers initiated
attacks primarily in areas dominated by sericea (16 of 25 attacks, or 64%). For male
Northern Harriers, four of five attacks (80%) were initiated in areas dominated by fescue.
42
In addition, all attacks (25 of 25) by female harriers were in areas with tall vegetation (>
0.5 m tall), while two of five attacks (40%) by male harriers were in short vegetation (<
0.5 m tall) and three of five (60%) were in tall vegetation.
I observed 36 interactions between harriers and other raptors, with most
interactions between Short-eared Owls (N = 17 of 36, or 47.2%) and other harriers (N =
13 of 36, or 36.1%). Three cases of piracy were also observed, with harriers taking prey
from Short-eared Owls in all three cases. Short-eared Owls were observed interacting
with other raptors on 14 occasions and most were interactions with Northern Harriers (9
of 14, or 64.2%).
Multivariate analysis of variance revealed significant differences between the
vegetation characteristics of sites used by foraging Short-eared Owls and randomly-
selected, apparently unused sites (Wilk’s lambda = 0.09, F18, 1 = 3.37, P = 0.023).
Stepwise discriminant analysis revealed 11 variables that permitted best discrimination
between foraging sites and apparently unused sites (Table 12). Classification analysis
using these variables correctly classified nine of 10 (90%) foraging sites and eight of 10
(80%) randomly-selected, apparently unused sites (70% better than by chance alone;
Cohen’s Kappa Z = 3.15, P = 0.0017). Short-eared Owls foraged in areas that had fewer
shrubs and shorter, less dense vegetation (dominated by grass rather than herbaceous
vegetation) than unused areas (Table 12).
The hunting behavior of other raptors was also monitored during the winter of
2002. Observations revealed that attacks by American Kestrels had a success rate of
28.7% (31 of 108 pounces). Success rates for other raptors included 25% for Merlins (3
43
of 12 attacks), 17.5% for Red-tailed Hawks (16 of 91 attacks), and 13% for Rough-
legged Hawks (2 of 15 attacks).
One adult male Northern Harrier was radio-tagged on 28 February 2003 and
subsequently tracked (N = 7 locations) until 18 March 2003. The mean distance between
points was 839.6 ± 606.7 m. The maximum and minimum distance between points were
1922.5 m and 139.3 m, respectively. Using seven locations, the range of this harrier over
the 19-day tracking period was found to encompass 0.6 km2 (Figure 25).
Discussion
Northern Harriers and Short-eared Owls foraged only on the wing during my
study, with no instances of perch-hunting observed. Similarly, MacWhirter and Bildstein
(1996:5) noted that harriers “virtually always” hunt on the wing, and Holt and Leasure
(1993:4) reported that Short-eared Owls hunted “primarily on the wing.” Toland
(1986:123) reported that Northern Harriers in Missouri “hunted from a slow coursing and
quartering flight more than 96% of the time.” Northern Harriers and Short-eared Owls in
my study initiated attacks primarily in areas dominated by either sericea or fescue.
Although based on small sample sizes, my results suggest that female Northern Harriers
initiated more attacks in areas dominated by tall stands of sericea, while males initiated
more attacks in shorter vegetation and in areas dominated by fescue. Sericea typically
forms a denser cover than fescue (pers. observ.), suggesting that female Northern
Harriers may hunt in areas with denser vegetation than males. Previous investigators have
also reported that female harriers hunt more in taller and denser vegetation than males
(Bildstein 1987, Temeles 1987). Temeles (1986) suggested that areas with taller
44
vegetation (> 0.5 m high) represented preferred foraging habitat for Northern Harriers
and, further, that females used such areas more often because dominant females caused
males to forage in less-preferred areas with low-growing vegetation. Martin (1987:63),
however, noted that Northern Harriers may be at a disadvantage in locating or capturing
prey in high, dense vegetation because of the “difficulty in plunging through dense
vegetation to capture prey . . . allowing escape time for potential prey.”
Overall, Northern Harriers in my study mainly used quartering flights (powered
flight back and forth over short distances, with many sharp turns). In contrast, Bildstein
(1987) reported that Northern Harriers in Ohio used transect flights most often (58% of
observations), with quartering flights used 22% of the time. Foraging methods used by
Northern Harriers are apparently influenced by the characteristics of the vegetation. For
example, Brown and Amadon (1968) suggested that harriers adjusted their speed relative
to the visibility of prey in different habitats, and flew faster over areas with less cover.
Thus, differences in foraging methods used by Northern Harriers in different locations
may, in part, be due to differences in habitat. Harriers in my study often initiated attacks
in areas dominated by dense stands of sericea and, in such areas, slower, quartering
flights may improve the chances of locating prey.
Female Northern Harriers in my study used primarily quartering flights when
hunting, while males used both quartering flights and transect flights. Temeles (1986)
also noted that female harriers used primarily slower quartering flights, while males were
more likely to hunt using fast, straight flights. Over tall vegetation, flying more slowing,
e.g., quartering flight, may improve a harrier’s chance of locating prey (Brown and
Amadon 1968). My results indicate that female Northern Harriers frequently hunted in
45
areas dominated by tall, dense stands of sericea, while males more often foraged in areas
dominated by fescue. This difference in habitat use by male and female Northern
Harriers in my study may have contributed to the difference in foraging methods used.
Another factor, however, may have been female dominance. Temeles (1986) suggested
that male Northern Harriers tend to fly faster and straighter in order to forage in areas
defended by dominant females while minimizing detection. Although I was unable to
identify individual harriers, my observations of foraging Northern Harriers revealed that
females were much more likely to be observed at particular locations on the Peabody
WMA, while the locations of male harriers were more unpredictable. While anecdotal,
such observations suggest that dominant female Northern Harriers may have been
defending foraging territories on the Peabody WMA, with males limited to areas on the
periphery of or outside those territories.
The attack success rate for Northern Harriers on the Peabody WMA (7%) was
within the range of rates previously reported. For example, MacWhirter and Bildstein
(1996) reported that prey-capture success by harriers was highly variable (5 – 35%) and
influenced by habitat and prey type. Temeles (1986) reported capture success rates of
6.25% (8 out of 128) for harriers attacking rodents and 0% (0 out of 20) for harriers
attacking birds in a California population. Northern Harriers on the Peabody WMA
preyed primarily on small mammals, and success rates when hunting agile prey such as
small mammals are typically lower than when hunting less agile prey such an amphibians
and reptiles (Toland 1986). In addition, as suggested by Martin (1987), Northern
Harriers foraging in tall, dense vegetation (e.g., areas on the Peabody WMA dominated
46
by sericea) may have difficulty capturing prey and, therefore, have lower attack success
rates.
Analysis revealed that areas used by foraging Short-eared Owls in this study had
shorter, less dense vegetation than unused areas. Short-eared Owls likely use both
acoustical and visual cues to detect prey (Holt and Leasure 1993). However, lab
experiments indicate that attack success for these owls increases with increasing
illumination (Clarke 1983). Such results suggest that vision plays an important role in
prey detection. The use of areas with shorter, less dense vegetation by Short-eared Owls
would increase prey detectability and, perhaps, increase attack success. Previous studies
have revealed that many species of raptors preferentially forage in areas with reduced
vegetation density, even when such areas have lower prey density, because such areas
improve the chances of detecting prey (e.g., Preston and Beane 1993, Bechard and Swem
2002).
Attack success rates for Short-eared Owls in my study (10.9%) was slightly
higher than that for Northern Harriers, but lower than reported previously (20.7%; Clark
1975). Once again, the relatively low attack success rates for Short-eared Owls in my
study may again be due in part by to the dense patches of sericea located on the Peabody
WMA.
I observed three cases of kleptoparasitism, with Northern Harriers taking prey
from Short-eared Owls in each case. Other investigators have also reported such
behavior (Clark 1975, Temeles and Wellicome 1992). In addition to the three successful
attempts to take prey from Short-eared Owls, Northern Harriers in my study made several
unsuccessful attempts. Previous work suggests that the frequency of such aggressive
47
interactions between these two species is influenced by weather (e.g., snow cover) and
population density (Craighead and Craighead 1956, Bildstein 1987, Temeles and
Wellicome 1992).
48
Chapter 3. Nest site selection and reproductive success of Northern Harriers
Methods
During the period from April – August 2002 and April – July 2003, an effort was
made to locate all Northern Harrier nests on the Peabody WMA. Nests were located by
observing the behavior of adults (e.g., males carrying food and prey exchanges; see
Appendix B for additional details concerning the behavior of Northern Harriers). All
nests were monitored regularly to determine clutch sizes, number of nestlings, and nest
outcome. To minimize the chances of predation, nests were checked infrequently (every
7 – 14 days) and were typically monitored from a distance (> 20 m) with the status of
nests determined by watching the behavior of the adults (e.g., prey exchanges or a male
perched nearby). In addition, a telescoping pole (about 5 m long) with an attached mirror
was used to minimize disturbance near the nest-site. I wore rubber waders when visiting
nests to deter any scent, and tried to check nests when clutches were likely to be
complete. For some nests, however, nestlings were already present when nests were
checked and, because infertile eggs may have been removed or predators may have taken
one or more eggs or nestlings, those nests were not used when determining mean clutch
sizes or comparing clutch sizes of adult and subadult females. For determining hatching
success, I only used nests that were checked when nestlings were at least 7 days old. At
those nests, the number of nestlings and, if present, number of unhatched eggs were
counted. For nests checked when nestlings were less than 7 days old, I assumed that any
unhatched eggs could still potentially hatch and, therefore, these nests were not used
when calculating hatching success. In several cases, nests with young less than 7 days old
were subsequently checked again to determine if any of the unhatched eggs had hatched,
49
but, unfortunately, nests had been predated and hatching success could not be
determined.
Because I did not capture and mark Northern Harriers on the Peabody WMA, the
number of breeding individuals in the population could only be estimated. One adult male
in 2002 was known to be polygynous because he was observed flying between the two
nest sites. In addition, based on timing and location of nests, I was relatively certain that
some pairs that lost nests to predators or abandoned nests were the same ones that
subsequently initiated new nests. However, in other cases, it was not clear whether nests
were initiated by the same pair that had earlier lost a nest in the same general area or by a
new pair.
Feeding rates were determined by watching harriers from a distance (> 50 m) or
from inside an observation blind (> 20 m) to minimize disturbance. The size of prey
delivered to nestlings by adult harriers was estimated by comparing the length of prey
items to that of the harriers’ bill. While bill length does vary between the sexes (16 mm
for males and 19 mm for females; MacWhirter and Bildstein 1996), the difference is
small and, as a result, I assumed a bill length of 17.5 mm when estimating the size of
prey.
After nests failed or fledged, nest locations were determined to the nearest 5 m
using a Garmin GPS unit. Nest-site vegetation was characterized using methods
described by James and Shugart (1970; Table 11). In addition, I randomly selected and
characterized the vegetation of sites not used by nesting harriers. Random sites were
identified either using a grid map and random number table or by choosing a random
number or angle and measuring 25 m from the nest-site.
50
At both nest sites and randomly-selected sites, vegetation within an 11.3 m radius
(0.04 ha) of the plot center was characterized. In addition to the vegetation analysis,
distances from the center of plots to the nearest roads (both gravel roads on the Peabody
WMA and paved state roads) and nearest permanent water were determined using
ArcMap 8.1 and spatial joins. Spatial joins are combining to spatial data which results in
a minimum distance. State roads were downloaded from a website (KYGEONET
2000b). State roads were from historical records dating back to 1929 and were outdated
and inaccurate for some areas near the Peabody WMA. These inaccurate segments were
correctly aligned with roads on 1998 digital orthophotographs (KYGEONET 2000a). The
Peabody WMA roads and permanent water features were digitized from digital
orthophotographs created in 1998 (KYGEONET 2000a)
Data Analysis
Possible differences in nest success between years, among months and different
nest substrates, and between female Northern Harriers of different ages (adult vs.
subadult) were examined using chi-square tests. Possible differences between adult and
subadult female harriers in clutch sizes and number of fledglings per successful nests
were examined using Wilcoxon tests (SAS 1989).
The characteristics of nest sites and randomly-selected, unused sites, as well as
the characteristics of successful and unsuccessful nest sites, were compared using
MANOVA. Two nests, one located on private property adjacent to the Peabody WMA
and another that was abandoned, were not included in the analyses. Stepwise discriminant
analysis was used to identify variables that best discriminated between sites (SAS 1989).
51
The provisioning behavior (number of visits) of adult male and female Northern
Harriers was compared using Wilcoxon tests. The possible effect of brood size on
provisioning rates and the size of prey delivered to nestlings was examined using
repeated measures analysis of variance (SAS 1989).
The density of Northern Harrier nests on the Peabody WMA was estimated by
delineating and determining the size of areas used by breeding harriers, then dividing the
number of nests present by the total area used. Using digital orthophotographs in
combination with my familiarity with the area, I delineated (digitized) the open
grasslands present on the Peabody WMA. Digitized areas did include some small
woodlots (< 1 ha), stands of shrubs, and water features (Figure 26). Total open grassland
area used by Northern Harriers during the summers of 2002 and 2003 was calculated
using a script from an ESRI website (ESRI 2003). To avoid overestimating nest density
or counting re-nests, I determined the maximum number of simultaneous breeding pairs
(pairs with active nests at the same time) on a given unit using dates of nest initiation or
by visually counting them. To calculate nest density, the total number of simultaneous
breeding pairs was divided by total area (Table 16).
Results
Forty-five nests were located on the Peabody WMA during the study. In the 2002
(N = 27 nests representing 18 – 24 pairs plus one polygynous male with two females and
two nests) and 2003 (N = 19 nests representing 12 or 13 pairs) breeding seasons, and one
nest (2002) was located on a privately-owned reclaimed area adjacent to the management
area. Ten of the 46 nests (21.7%) were successful (i.e., fledged young; Table 13). Of the
52
36 nests that failed, 33 (91.6%) were apparently depredated and three were abandoned.
Most nests that failed due to apparent predation were lost during the nestling period (N =
31; Figure 29). For nests located on the Peabody WMA, and excluding nests that were
abandoned (N = 3), 10 of 42 (23.8%) of nests were successful. Nest success did not differ
between 2002 and 2003 (χ2 = 0.49, P = 0.48), with five of 25 nests (20%) successful in
2002 and five of 17 (29.4%) successful in 2003.
In my study, 25 of 46 female harriers (56.5%) were adults, while 20 (43.5%) were
subadults. The age of one female harrier could not be determined. In contrast, only one
male harrier in the breeding population was a subadult, with the rest (N = 44) being
adults. This subadult male was paired with a subadult female, and their nest was
depredated during the incubation stage. For females whose age was determined, nest
success did not differ with age (χ2 = 1.39, df = 1, P = 0.24), with four of 23 nests (17.4%)
of adult females successful and six of 18 nests (33.3%) of subadult females successful.
Adult females did initiate nests earlier than subadult females (χ2 = 8.96, df = 2, P =
0.0114), with more adult (13 of 23 nests, or 56.5%) than subadult females (3 of 18, or
16.7%) initiating nests in April. However, the month of nest initiation had no effect on
nesting success (χ2 = 4.21, df = 2, P = 0.12).
The mean dates for initiation of egg laying by female Northern Harriers in my
study were similar in 2002 (0 = 6 May, range = 1 April - 17 June) and 2003 (0 = 7 May,
range = 4 April - 20 June). For nests with clutches known to be complete (N = 14), mean
clutch size was 5.07 ± 1.0 eggs, and mean clutch size did not differ between years (z =
1.30, P = 0.19. However, clutch sizes did differ with age (t = 4.10, P = 0.0003), with
mean clutch sizes of 5.4 ± 0.8 for adult females (N = 21) and 4.3 ± 0.8 for subadult
53
females (N = 13), respectively. Overall, hatching success (percent of all eggs that
hatched) was 85.4% (60 of 71 eggs). Hatching success for adult and subadult female
Northern Harrier did not differ (z = 0.90, P = 0.37). However, hatching success did differ
between years (z = 2.09, P = 0.037), with a mean hatching success of 77.1 + 5.5% (N = 8)
in 2002 and 95.8 + 4.2% (N = 6) in 2003.
Overall, nestling success (percent of nestlings that fledged) was 40.3 + 11.0% (N
= 14 nests), with no difference either between adult and subadult females (z = 0.21, P =
0.83) or between years (z = 0.74, P = 0.46). I counted nestlings at 26 harrier nests, and
determined that 28 of 87 nestlings (32.1%) at those nests survived to fledging. Overall,
the mean brood size was 4.29 ± 1.0 (N = 14; Table 13), with no difference either between
years (z = 0.68, P = 0.49) or between adult and subadult females (z = 0.28, P = 0.78).
Similarly, I found no difference between adult and subadult female Northern Harriers in
the number of young fledged per successful nest (z = 1.60, P = 0.11), with a mean of 3.75
+ 0.85 (N = 4) fledged young for each successful nest of adult females and 2.17 + 0.40 (N
= 6) for successful nests of subadult females.
During my 2-year study, the greatest number of harrier nests was located on the
Sinclair Unit of the Peabody WMA (N = 24; Table 13). In addition, there were two
successful nests on the Sinclair Unit during each year of the study and more young
fledged from nests on the Sinclair Unit (N = 13) than any other unit (Table 13). More
harrier nests were located on the Homestead Unit in 2002 (N = 10) than in 2003 (N = 1).
During the 2002 breeding season, one polygamous male (nests 11 and 17) harrier was
discovered on the Riverqueen Unit.
54
Northern Harrier nests were constructed on and in several different species of
vegetation, but the most frequently used substrates for nests were sericea (N = 21) and
blackberry (N = 11; Figure 28). One nest was located in a cattail (Typha latifola) marsh.
For both years combined, a similar number of nests were located in exotic or non-native
vegetation (N = 24) and in native vegetation (N = 20; Figure 29). The type of vegetation
(native or non-native) in which nests were located did not influence nesting success (χ2 =
0.04, df = 1, P = 0.83). Similarly, the type of vegetation (legume, forb, grass, and shrub)
in which nests were located did not influence nesting success (χ2 = 2.73, df = 3, P = 0.43).
Multivariate analysis of variance revealed a significant difference in the
vegetation characteristics of successful (fledged young) and unsuccessful harrier nests
(Wilk’s lambda = 0.26, F23, 18 = 2.21, P = 0.045). Stepwise discriminant analysis revealed
six variables that permitted best discrimination between successful and unsuccessful nests
(Table 14). Classification analysis using these six variables correctly classified 23 of 32
(71.9%) of the unsuccessful nests and seven of 10 (70%) of the successful nests (35%
better than by chance alone; Cohen’s Kappa Z = 2.38, P = 0.017). Successful nests were
located in denser vegetation and in areas with greater vertical cover than unsuccessful
nests (Table 15).
Analysis also revealed a significant difference between the vegetation
characteristics of nest sites and randomly-selected, unused sites (Wilk’s lambda = 0.67,
F17, 64 = 1.85, P = 0.041). Stepwise discriminant analysis revealed six variables that
permitted best discrimination between used and unused sites (Table 15). Classification
analysis using these six variables correctly classified 30 of 38 (80%) unused sites and 32
of 42 (76.2%) used sites (55% better than by chance alone; Cohen’s Kappa Z = 4.93, P <
55
0.0001). Areas used as nest sites by Northern Harriers were closer to water and shrubs in
areas with fewer small trees and more foliage cover (Table 15).
Overall (2002 and 2003 combined), the mean density of Northern Harriers nests
on the Peabody WMA was 0.40/km2 (Table 16). Mean nest density on the Peabody
WMA was twice as high in 2002 (0.61/km2) than in 2003 (0.30/km2; Table 11). For 2002
and 2003 combined, the highest density of Northern Harrier nests was on the Vogue Unit
(Table 11). However, nest density on the Sinclair Unit was higher than on the Vogue Unit
in 2003 (Table 16). For both years combined, the mean distance between harrier nests at
the Sinclair Unit was 1669.4 ± 872.3 m (Figure 30). During the 2002 and 2003 breeding
seasons, six pairs of Northern Harriers renested after either losing a nest to predation or
abandoning a nest. For these pairs, the mean distance from the initial, unsuccessful nest
to the new nest was 138.5 ± 107.6 m.
The mean provisioning rate of Northern Harriers during the 2002 and 2003
breeding seasons was 0.94 items/hr (160.8 hr of observation at 12 nests). During my two-
year study, most prey delivered to nestlings by harriers were small mammals (N = 134 of
139, or 96.4%). In 2002, all identified prey items (N = 91) delivered to nestlings were
small mammals. In 2003, 89.6% (43 of 48) of prey items delivered to nestlings were
small mammals, while 10.4% (5 of 48) were birds. Males captured most prey items (N =
132 of 167 prey items, or 79.0%), but only 23.4% of prey (N = 39 of 167) was presented
to nestlings by males. Prey captured by male harriers was usually delivered to females
during an aerial exchange (N = 96 of 132 prey items, or 72.7%), and females then
delivered the prey to nestlings. In contrast, all 35 prey items captured by female harriers
were also delivered to nestlings by females. Female harriers captured more prey when
56
nestlings were two or more weeks old (14 – 28 days post-hatching). At nests with young
1 – 13 days post-hatching, female harriers captured only four prey items. However,
during observation periods when nestlings were 14 – 28 days post-hatching, females
captured 31 prey items.
Overall, the mean length of prey delivered by harriers to nestlings was 38.9 + 1.31
mm (N = 163 prey items). The size of prey captured by male and female harriers did not
differ (F2, 6 = 0.24, P = 0.8), with a mean length of 36.3 + 2.7 mm (N = 35 prey items) for
prey captured by females and 39.7 + 1.5 mm (N = 129 prey items) for prey captured by
males. Similarly, neither the size of captured prey (F13, 3 = 3.53, P = 0.16) nor the size of
prey actually delivered to the nest (F13, 3 = 2.56, P = 0.24) varied with nestling age. Brood
size also had no apparent effect on prey size, with neither the size of captured prey (F4, 4 =
1.74, P = 0.3) nor the size of prey delivered to nestlings (F4, 4 = 2.06, P = 0.25) varying
with number of nestlings.
Discussion
The nest success (percent of nests from which at least one young fledged) of
Northern Harriers on the Peabody WMA (21.7%) was lower than that reported at most
other locations. In North Dakota, Hammond and Henry (1949) reported the lowest
harrier nesting success (18%) in North America. At other locations, nest success for
Northern Harriers varied from 38% (Michigan; Craighead and Craighead 1956) to 79%
(New Hampshire; Serrentino 1987). Hatching success for harriers in my study was
45.1%. Other investigators have reported hatching success rates for Northern Harriers
ranging from 32% (Michigan) to 76% (New Brunswick), but hatching success for seven
57
studies summarized by MacWhirter and Bildstein (1996) averaged 60%. Similarly,
nestling success for harriers in my study averaged 32.1%, and only one previous study
has revealed a lower value (20%; Hammond and Henry 1949). Nestling success reported
in six other studies ranged from 60% to 89% (MacWhirter and Bildstein 1996).
MacWhirter and Bildstein (1996) suggested that ground moisture had a significant
effect on the nesting success of Northern Harriers, with success higher in the wettest sites
and lower in drier sites. Similarly, Simmons and Smith (1985) found that harrier nests
located in very wet and wet sites were significantly more successful than nests in dry
sites, and suggested that these differences were the result of the differential habitat
preferences of mammalian predators. Specifically, Simmons and Smith (1985) noted that,
of the mammalian predators present in their study area in New Brunswick (red fox,
Vulpes vulpes; striped skunk, Mephites mephitis; raccoon, Procyon lotor; feral cat, Felis
domesticus; mink, Mustela vison; and stoat, Mustela erminea), only raccoons and mink
were actually observed in marshy areas. Most populations of Northern Harriers in North
America breed in wetland habitats (MacWhirter and Bildstein 1996), and reduced
predation rates in such areas are one likely reason for this apparent preference. With one
exception (one nest in a small cattail marsh), nests of Northern Harriers in my study were
located in dry, upland areas. As a result, harrier nests on the Peabody WMA were likely
more vulnerable to predation than those in wetland habitats.
My results indicate that Northern Harriers exhibited no preference for either
native or non-native vegetation for nest sites and, further, that vegetation type (legume,
forb, grass, or shrub) had no effect on reproductive success. Similarly, Herkert et al.
(1999) found that the type of vegetation (native vs. non-native) did not appear to
58
influence nest placement by Northern Harriers in Illinois. In contrast, MacWhirter and
Bildstein (1996) suggested that harrier nests located in forbs were significantly more
successful than those in shrubs. However, any such effect of vegetation type is likely
influenced by location (wet vs. dry sites) and, as discussed below, the amount of cover or
concealment provided by that vegetation. Herkert et al. (1999) suggested that, while
vegetation type (native vs. non-native) may not influence nest site selection, Northern
Harriers “. . . are more likely to nest in undisturbed fields with tall, dense cover . . .”
Further, Herkert et al. (1999) noted that most undisturbed fields used by nesting Northern
Harriers had been undisturbed (not mowed or burned) for more than a year.
There appeared to be a diverse predator population on the Peabody WMA.
Among the possible nest predators that I actually observed on the area were coyotes
(Canis latrans), bobcats (Felix rufus), raccoons and Great Horned Owls. Several other
observed potential predators or their signs of Northern Harrier nests also occurred on the
Peabody WMA, including mink, red fox , and feral dogs (C. familiaris). In addition to
predation on eggs and nestlings, one subadult female Northern Harrier in my study was
killed by a predator, apparently while incubating eggs. Two other investigators have
reported predation of an incubating or brooding female Northern Harrier (Saunders 1986,
MacWhirter unpubl data in MacWhirter and Bildstein 1996).
Successful harrier nests in my study were in areas that provided greater vegetation
cover from 0.5 to 1.5 m above ground than areas with unsuccessful nests. Other
investigators have also noted that harrier nests in areas with less vegetation cover were
more likely to be unsuccessful (Hamerstrom 1969, Watson 1977). MacWhirter and
Bildstein (1996) suggested that nest concealment might be an important factor in
59
determining nest success for Northern Harriers in drier habitats. Northern Harriers in my
study selected dense patches of sericea and blackberry as nest sites more often than sites
in other types of vegetation. Such selection may have been related to availability, but may
also have been due to the cover and concealment such sites provided. Toland (1986) also
reported frequent of use of blackberry as nesting cover by Northern Harriers in Missouri,
and noted that harriers selected blackberry even when other apparently suitable
vegetation was abundant. Although I found no difference in nest success among
vegetation types, Toland (1985) suggested that harriers might select blackberry patches as
nest sites because such sites: (1) provide concealment, (2) might, because of the density
of the vegetation, make eggs and young difficult to smell, and (3) may, because of the
thorns, deter potential predators.
One possible explanation for the low nesting success of Northern Harriers with
nests in sericea in my study (6 of 21 successful, or 28.5%) may have been the inability of
nestlings to move from the nest and hide from predators. When 2 – 4 weeks old, harrier
nestlings typically begin to create ‘tunnels’ or narrow paths in nearby vegetation
(MacWhirter and Bildstein 1996). These paths provide access to ancillary resting and
feeding areas (MacWhirter and Bildstein 1996). In addition, however, such paths in tall
vegetation are ‘tunnel-like’ and may provide cover from predators, particularly aerial
predators (pers.obs.). I observed ‘tunnels’ at harrier nests located in areas dominated by
native grasses (e.g. switchgrass). However, few such ‘tunnels were observed at nests
located in dense stands of sericea, perhaps because of the structural complexity of such
stands. Although the density and cover provided by sericea may increase nest
60
concealment, the inability of nestlings to create ‘tunnels’ and, therefore, escape from
predators that have located the nest may increase the risk of predation to older nestlings.
Analysis revealed a significant difference between the vegetation characteristics
of nest sites and randomly-selected, unused sites, with sites used by nesting Northern
Harriers on the Peabody WMA in areas with fewer trees, deeper litter, and taller, denser
vegetation. Similarly, Sutherland (1987) compared the characteristics of vegetation at
nest sites and random sites for a nesting population of Northern Harriers in North Dakota
and found that nest sites had taller green vegetation and provided more cover than
random sites. Other investigators have also noted that Northern Harrier nests are typically
located in tall, dense vegetation (Kantrud and Higgins 1992, MacWhirter and Bildstein
1996). This apparently consistent selection for nest sites that provide more cover (i.e.,
taller, denser vegetation) provides further evidence that concealment may be an important
factor in the nesting success of Northern Harriers nesting in dry, upland locations.
The ratio of breeding subadult (N = 20, or 44.4%) to adult (N = 25) female
Northern Harriers on my study area was among the highest reported in either North
America or Great Britain. In Wisconsin, only 16% of 268 breeding females were
subadults (Hamerstrom et al. 1985), while, in New Brunswick, 23% of 116 females in the
breeding population were subadults (MacWhirter and Bildstein 1996). Watson (1977)
reported that the proportion of first-year female harriers in a breeding population in Great
Britain was 13%. One factor possibly contributing to the relatively high number of
breeding subadult females in my study area was the relatively low density of breeding
females. For example, the mean distance between active nests on the Sinclair Unit of the
Peabody WMA was nearly 1700 m. In contrast, MacWhirter and Bildstein (1996) noted
61
that the median internest distance for Northern Harriers at seven locations was 430 m.
Further, male and female harriers are intolerant of conspecifics near nest sites
(MacWhirter and Bildstein 1996) and, at high densities, dominant adult females could
potentially prevent subadult females from establishing nesting territories. Watson
(1977:140) reported that the age structure of a breeding population of Northern Harriers
in Great Britain supported the view “ . . . that social behaviour was excluding some
younger birds from breeding.” The relatively low density of breeding harriers on the
Peabody WMA may be related to habitat quality (e.g., suitable nest sites or prey
availability) or may simply be an artifact of the location of the area at the extreme
southern edge of the breeding range of harriers.
The mean clutch size for Northern Harriers on the Peabody WMA was 5 eggs,
which is comparable to mean clutch sizes reported throughout its range (Thompson-
Hanson 1984, Johnsgard 1990). Over its entire North American range, MacWhirter and
Bildstein (1996) reported a mean clutch size of 4.4 for Northern Harriers, with no
pronounced geographical trends. In addition, Simmons (1988) reported that clutch sizes
of Northern Harriers were unrelated to the availability of small mammals in female
territories. Adult female Northern Harriers in my study had significantly larger clutches
(0 = 5.4) than subadult females (0 = 4.3). Simmons et al. (1986) reported that clutch sizes
of adult female harriers (0 = 4.4, N = 42) were marginally larger than those of subadult
females (0 = 4.2, N = 17). While few investigators have reported clutch sizes of adult and
subadult female Northern Harriers, older females are reported to produce larger clutches
in other species of raptors. For example, Smallwood and Bird (2002) reported that the
mean clutch sizes of American Kestrels in a captive population increased by 0.20
62
eggs/year up to 5 years of age. Similarly, Newton (1986) found that the mean clutch sizes
of female Eurasian Sparrowhawks (Accipiter nisus) increased progressively for the first
three years and reached a peak at 4.5 years. Newton (1986) further suggested that such
variation might be the result of age-related differences in foraging abilities or in acquiring
good quality territories. Such differences could, in turn, contribute to differences in the
physical condition of females and, as a result, differences in energy available to produce a
clutch of eggs.
Adult female Northern Harriers in my study tended to initiate nests earlier in the
breeding season than subadult females. Similarly, MacWhirter and Bildstein (1996)
reported that laying dates of older female Northern Harriers (> 3 years old) preceded
those of younger ones by an average of 6 days. As with differences in clutch sizes, the
earlier nesting of adult females may be related to age-related differences in physical
condition. For example, Peterson (1979) suggested that the timing of clutch initiation by
female Red-tailed Hawks was dependent on female nutritional status. Another factor,
however, may be the time of arrival on the breeding grounds. Northern Harriers are
migratory and the wintering sites of those that breed on the Peabody WMA are unknown.
However, previous investigators have noted that adult Northern Harriers generally arrive
on breeding areas before subadults (Hamerstrom 1969, Bildstein and Hamerstrom 1980).
Earlier arrival may permit earlier pairing and contribute to differences between adult and
subadult female harriers in the initiation of egg-laying.
Although adult female Northern Harriers in my study area initiated egg-laying
before subadult females and produced larger clutches, I found no differences between
adult and subadult female harriers in either nest success (number of nests from which at
63
least one young fledged) or number of fledglings per successful nest. Similarly,
Hamerstrom et al. (1985) examined the breeding biology of Northern Harriers in
Wisconsin and found “. . . few substantial age-related differences among females in
nesting success or fledging rates.” In other species of raptors, age and prior breeding
experience may influence reproductive success. For example, Smallwood and Bird
(2002) reported that age and experience appeared to influence productivity of American
Kestrels, with success rates for pairs with at least one bird known to have bred previously
significantly higher than that for pairs with unknown prior experience.
One factor possibly contributing to the absence of any differences in the
reproductive success of adult and subadult female Northern Harriers in my study was the
quality of mates. Simmons et al. (1986) noted that reproductive success of Northern
Harriers in New Brunswick was most strongly related to the food-provisioning rates of
males and laying date. All but one breeding male harrier in my study were adults.
Previous investigators have also found that few yearling males typically breed. For
example, Hamerstrom et al. (1985) reported that only 8% of 210 breeding males were
first-year birds in a Wisconsin population; while Simmons et al. (1986) found that just
5% of 130 breeding males were first-year birds in a New Brunswick population. The
experience and food-provisioning skills of adult males were likely important factors in
the breeding success of subadult female Northern Harriers in my study.
Adult Northern Harriers in my study provisioned nestlings at a rate of 0.94 prey
items per hour. Simmons et al. (1987) reported average feeding rates of 1.3 items per
hour based on five studies of Northern Harrier provisioning in North America, and 0.66
items per hour based on eight studies in Europe. While these rates would seem to differ,
64
provisioning rates for harriers in different areas and populations, as noted by Simmons et
al. (1987), are not comparable because of possible differences in prey sizes.
Male Northern Harriers in my study captured most of the prey delivered to
nestlings, with females capturing prey primarily when nestlings were 14 – 28 days old.
Similarly, Simmons et al. (1987) reported that adult female harriers rarely began food
provisioning until nestlings were 14 – 20 days old, and MacWhirter and Bildstein (1996)
noted that male harriers provide virtually all food until nestlings are 10 – 14 days old. As
also reported by other investigators (MacWhirter 1985, Simmons et al. 1987), male
harriers in my study typically transferred prey to mates in aerial exchanges and the
females then delivered food to the nestlings.
Most prey items delivered to nests by adult harriers in my study were small
mammals. MacWhirter and Bildstein (1996:15) noted that nestling harriers are “fed the
same food as adults eat”, and Bent (1937:83) reported that mice and small birds were the
principal prey provided to nestlings. Barnard et al. (1987) found that 70.4% of all prey (N
= 642) delivered to nestling harriers in a New Brunswick population were voles
(Microtus spp.), while in Wisconsin, Errington (1933) reported that 34.8% of prey items
(N = 359) delivered were voles and 35.7% were ground squirrels. In California, Selleck
and Glading (1943), in contrast, found that voles and other rodents made up only 6.7% of
the prey items (N = 438) delivered to nestling harriers, with the most common prey being
blackbirds (22.8%), sparrows (17.6%), and finches (13.9%). Similarly, Watson (1977)
found that 181 of 209 prey items (identified either in pellets or as remains) delivered to
nestling harriers at a study site in southwest Scotland were birds. Clearly, prey taken by
adult Northern Harriers during the breeding season varies among locations and with
65
availability. The high percentage of small mammal prey (96.4%) delivered to nestlings
by adult Northern Harriers on the Peabody WMA suggests that the area provides good
habitat for small mammals and, apparently, supported good populations of small
mammals during the 2002 and 2003 breeding seasons.
The size of prey delivered to nestlings by adult Northern Harriers in my study did
not vary with either nestling age or brood size. MacWhirter and Bildstein (1996) reported
that prey size increased with nestling age at some locations, but not others. Sutherland
(1987) suggested that increases in prey size delivered to nestling harriers with nestling
age might be due to increasing female participation in capturing prey, with larger females
possibly capturing larger prey than adult males. The absence of any variation in the size
of prey delivered to broods of different sizes or ages in my study may have been due, in
part, to limited variation in brood sizes. Most successful nests (N = 10) in my study
fledged one (N = 1), two (N = 5), or three (N = 1) young. More variation in demand for
prey, particularly for older nestlings, would likely be apparent in larger broods (e.g., 5, 6,
or 7 young).
66
Chapter 4. Management Implications
The Peabody Wildlife Management Area appears to provide an abundance of
suitable habitat for sizable wintering populations of raptors, including Northern Harriers
and Short-eared Owls. The abundant grassland habitat apparently supports an ample prey
base of small mammals and invertebrates, while woodlots and patches of conifers and
cedars provide cover for roosting raptors. Current management practices, including
prescribed burns, create a patchwork of grassland habitats, with taller, more dense grasses
and herbs that provide cover for roosting Short-eared Owls and roosting and nesting
Northern Harriers. Interspersed areas of shorter grass and herbaceous vegetation that
provide less cover for potential prey and likely enhance the foraging success of the many
raptors that hunt in the open areas of the Peabody WMA probably contribute to the high
density and diversity of raptors on the Peabody WMA.
While the Peabody WMA does appear to provide excellent habitat for numerous
breeding and non-breeding raptors, the area may not provide sufficient high quality
nesting habitat for Northern Harriers. The density of nesting harriers was lower than
reported at many other locations, and nest success of Northern Harriers on the Peabody
WMA was lower than has been reported at most other nesting locations in North
America. The greater nest success for harriers on the Peabody WMA that nested in taller,
denser vegetation suggests that providing harriers with more such habitat (e.g., by using
longer rotation times for prescribed burns at some locations) might improve their nesting
success. However, previous work indicates that the nesting success of Northern Harriers
will likely always be lower in drier, upland habitats like the Peabody WMA than in
wetter habitats.
67
Wetland preservation and management for waterfowl and upland birds may be
beneficial for Northern Harriers (Hamerstrom 1969, Duebbert and Lokemoen 1977).
More Northern Harriers nested in units of the Peabody WMA with more surface water
(i.e., the Sinclair Unit), and one nest (nest 28) was located at Riverqueen in an ephemeral
cattail marsh approximately 568.5 m2. Construction of more wetlands or water features
on the area may provide higher quality habitat and increase the nesting success of
Northern Harriers. In addition, Northern Harriers frequently nested in large thickets of
blackberry (Rubus sp.) on the Peabody WMA. In Missouri, Toland (1986) found that
harriers often constructed nests in blackberry thickets and nests in such thickets were
more likely to be successful. Thus, the development of additional blackberry thickets on
the Peabody WMA, in addition to maintaining those already present, may be beneficial
for Northern Harriers, as well as for game species such as Northern Bobwhite (Colinus
virginianus).
Although my analysis revealed that the nesting success of harriers was not
influenced by vegetation type (native or nonnative), potentially important characteristics
of vegetation (e.g., flexibility of stems) were not quantified. My observations at nests
located in stands of sericea suggested that nestlings might have had trouble moving into
the surrounding vegetation and creating 'tunnels.' At nests located in native vegetation
(particularly in switchgrass), nestlings appeared to have no such problems. A
management strategy of planting more native grasses and forbs and increasing habitat
heterogeneity may increase prey vulnerability for breeding harriers and wintering raptors.
Further, young harriers may walk, hide, and create 'tunnels' more easily in areas
dominated by native grasses and forbs.
68
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77
Appendices
Appendix A. Tables.
78
Table 1. Length of the survey route in or adjacent to various units of the Peabody Wildlife Management Area and off the area.
Units or sections Length (km) Ken Hopewell and Homestead 14.64 Riverqueen** 11.74 Sinclair 9.65 Vogue 3.86 Gibraltor 2.57 Off Peabody WMA 28.24
**Ken American was apart of Riverqueen until summer of 2002. Ken Hopewell and Homestead units are adjacent to each other and are included together.
Table 2. Species of raptors (N = 19) observed on the various units of the Peabody WMA, 2002 - 2003 (X = observed). Species Vogue Sinclair Ken Hopewell
and Homestead Riverqueen Gibraltor
Northern Harrier (Circus cyaneus) X X X X X Mississippi Kite (Ictinia mississippiensis) - X - - - Swallow-tailed Kite (Elanoides forficatus) - X - - - Sharp-shinned Hawk (Accipiter striatus) X X X X X Cooper's Hawk (Accipiter cooperi) X X X X X Red-shouldered Hawk (Buteo lineatus) - X X X X Broad-winged Hawk (Buteo platypterus) X X X X X Red-tailed Hawk (Buteo jamaicensis) X X X X X Rough-legged Hawk (Buteo lagopus) - X X - X Golden Eagle (Aquila chrysaetos) - - - X - Bald Eagle (Haliaeetus leucocephalus) - X X X - Osprey (Pandion haliaetus) X X X - X Merlin (Falco columbarius) X X X X American Kestrel (Falco sparverius) X X X X X Prairie Falcon (Falco mexicanus) - X - - - Long-eared Owl (Asio otus) - X - X - Short-eared Owl (Asio flammeus) X X X X X Great Horned Owl (Bubo virginianus) X X X X - Barred Owl (Strix varia) - X - X -
79
Table 3. Total number of raptors observed during road surveys, 1 January 2002 - 25 July 2003. Species Number observed Percentage of total observed
Red-tailed Hawk 761 36.30 Northern Harrier 504 24.09 American Kestrel 487 23.28 Broad-winged Hawk 139 6.64 Red-shouldered Hawk 60 2.87 Osprey 35 1.67 Rough-legged Hawk 31 1.48 Cooper's Hawk 29 1.39 Sharp-shinned Hawk 17 0.81 Unidentified Buteo 10 0.48 Merlin 7 0.33 Great Horned Owl 3 0.14 Bald Eagle 2 0.10 Short-eared Owl 2 0.10 Golden Eagle 1 <0.05 Mississippi Kite 1 <0.05 Unidentified Accipiter 1 <0.05 Unidentified falcon 1 <0.05 Unidentified raptor 1 <0.05
80
Table 4. Total number of raptors observed during road surveys on various units of the Peabody Wildlife Management Area, 2002 – 2003.
Species Vogue Sinclair Ken Hopewell and Homestead
Ken American and Riverqueen Gibraltor
Off Peabody WMA
Total
Northern Harrier 52 219 142 62 9 20 504 Mississippi Kite 1 1 Sharp-shinned Hawk 4 1 2 1 1 8 17 Cooper's Hawk 3 2 5 8 1 10 29 Red-shouldered Hawk 3 5 28 2 22 60 Broad-winged Hawk 1 76 39 3 19 1 139 Red-tailed Hawk 55 155 259 106 35 151 761 Rough-legged Hawk 16 15 32 Golden Eagle 1 1 Bald Eagle 1 1 2 Osprey 1 16 6 0 12 35 Merlin 3 1 3 7 American Kestrel 31 94 90 97 18 157 487 Great Horned Owl 1 1 1 2 Short-eared Owl 2 2 Unidentified Buteo 4 4 2 10 Unidentified Accipiter 1 1 Unidentified falcon 1 1 Unidentified raptor 1 1 Total 151 592 568 312 86 383 2092
81
Table 5. Total number of raptors observed during surveys on the Peabody Wildlife Management Area during the winters (January – March) of 2002 (10 surveys) and 2003 (7 surveys). 2002 AMKE COHA GOEA MERL NOHA OSPR RLHA RSHA RTHA SEOW SSHA UB Monthly Total
Jan 27 1 - - 62 - 6 2 68 - - - 166 Feb 29 2 - 5 102 - 7 3 99 2 3 - 252
Mar
10 1 - - 40 3 6 2 27 - - - 89
Totals 66 4 0 5 204 3 19 7 194 2 3 0
507 2003 Jan 20 1 - 43 - 2 6 53 - 1 2 128
Feb 14 1 - - 27 - 3 6 50 - 2 4 107Mar
9 2 - - 55 - 5 4 30 - - 3 108
Totals 43 3 1 0 125 0 10 16 133 0 3 9 343
AMKE = American Kestrel, COHA = Cooper's Hawk, MERL = Merlin, GOEA = Golden Eagle, NOHA = Northern Harrier, OSPR = Osprey, RSHA = Red-shouldered Hawk, RLHA = Rough-legged Hawk, SEOW = Short-eared Owl, SSHA = Sharp-shinned Hawk, UB = Unidentified Buteo
Table 6. Number of Northern Harriers of different sex and age classes observed on the Peabody Wildlife Management Area during the winter (Jan – Mar), 2002 - 2003. 2002 Adult Adult Total Brown Total Immature Total Unknown Unknown Unknown Unknown Total Monthly Total Female Male Female Male Jan 13 16 29 22 5 - - 6 6 62 Feb 16 24 40 45 10 - - 7 7 102
Mar 16 12 28 9 3 - - - - 40
Totals 45
52 97 76 18 0 0 13 13 204 2003 Jan 9 14 23 17 1 - - 2 2 43 Feb 8 6 14 8 2 1 - 2 3 27
Mar 6 20 26 21 3 2 1 2 5 55
Totals 23 40 63 46 6 3 1 6 10 125
82
Table 7. Proportion of dominant habitats (N = 96 points) found along the survey route through Ohio and Muhlenberg counties, KY, 2002-2003.
Habitat type Dominant
Habitat Woodlot 47.9% Tall grass 24.0% Short grass 10.4% Cropland 9.4% Scattered shrubs 3.1% Pasture 3.1% Wetland 2.1% Woodlot edge 0.0% Roadside edge 0.0%
Table 8. Habitats in which raptors were observed during road surveys on the Peabody Wildlife Management Area, 2002 - 2003.
Habitat type
Number of raptors observed
Percentage of raptors observed
Tall grass 1179 56.4 Roadside edge 287 13.7 Woodlot 220 10.5 Short grass 155 7.4 Woodlot edge 104 5.0 Wetland 49 2.3 Cropland 43 2.1 Scattered shrubs 42 2.0 Pasture 9 0.4 Unknown 4 0.2
83
Table 9. Percentage of habitat types used during the non-breeding and breeding season on the Peabody Wildlife Management Area, 2002-2003.
Habitat Type
Non-breeding Breeding
Tall grass 55.1% 59.1% Roadside edge 15.2% 10.9% Short grass 7.7% 7.0% Woodlot 7.4% 16.8% Woodlot edge 6.7% 1.7% Wetland 2.8% 1.4% Scattered shrub 2.4% 1.3% Cropland 2.2% 1.7% Pasture 0.6% 0.2%
Table 10. Behavior of raptors observed during road surveys on the Peabody Wildlife Management Area, 2002 - 2003.
Behavior Number observed Percentage Perch hunting 767 36.7 Soaring 491 23.5 Direct flight 372 17.8 Hunting in flight 275 13.1 Perch resting 97 4.6 Hover hunting 52 2.5 Carrying food 16 0.8 Feeding 16 0.8 Vocalization 3 0.1 Unknown 3 0.1
84
Table 11. Vegetation parameters measured within circular plots in areas used by foraging Short-eared Owls and nesting Northern Harriers, and at randomly-selected unused sites. Variable Method of estimation Foliage cover at heights of < 0.5m, 0.5 - 1 m, and > 1 m
A pole or meter stick at was used to measure vegetation cover. Data was recorded at the nest or plot center and then at 10 m intervals for Short-eared Owl foraging grounds or 2.2 m intervals for Northern Harrier nests along sampling lines in four cardinal directions from the center. Five points along the sampling line (excluding nest or plot center) was used. If foliage occurred within a radius of 0.1 m of the stick within a 0.1 segment, one hit was counted. Hits were averaged for each interval (<0.25 m, 0.25 - 0.5 m, 0.5 - 1 m, and 1 - 2 m) and a percentage was calculated.
Ground cover and type of cover
The presence or absence (i.e., bare ground) of ground cover and type of cover (grass, herb, shrub, or tree) at the plot center or nest and at 20 additional points within the plot (5 in each cardinal direction at 10 or 2.2 m intervals) was determined using a densitometer. A percentage was calculated.
Vegetation height
Using a 3 m pole or stick marked in 0.1 m intervals, the maximum height of vegetation was measured at 24 points within the plot (at the nest or center plus 5 in each cardinal direction at 10 or 2.2 intervals).
Litter depth
Litter depth was measured at 24 points within the plot (at the nest or center plus 5 in each cardinal direction at 10 or 2.2 m intervals).
Vertical cover at heights of < 0.5 m, 0.5 - 1.0 m, and 1 - 2 m
Vertical cover was determined using a white canvas cloth ( 0.5 m wide x 2 m high) divided vertically into 3 heights (< 0.5 m, 0.5 - 1.0 m, and 1 - 2 m). Each height was divided into a grid of 49 squares. The cloth was placed at the edge of plots at 11.3 m for Northern Harrier nests in 4 cardinal directions and, from a height of 1 m, an observer at the nest recorded the number of squares at least half obscured in each vertical section (Noon 1981). For Short-eared Owls, vertical cover was determined at 5 points in each cardinal direction. An observer, from a height of 2 m and a distance of 10 m along the sampling line, recorded the number of squares at least half obscured in each vertical section of the cloth.
85
Table 12. Variables permitting best discrimination between foraging areas of Short-eared Owls and randomly-selected, unused areas on a reclaimed surface mine grassland in west-central Kentucky.
Used areas
(N = 10) Unused areas
(N = 10)
Variable mean SE mean SE Nearest shrub 27.40 7.60 9.40 1.99 Nearest edge 768.50 150.89 464.50 95.91 Nearest water 284.67 42.02 242.74 33.56 Number of shrubs in circle 10.70 4.71 50.20 19.04 Trees > 8 cm in circle 0.10 0.10 0.00 0.00 % Herbaceous vegetation 22.92 7.22 66.83 8.90 Vertical height (cm) 24.25 2.80 55.58 5.55 % Foliage covera, < 0.5 m 5.77 0.42 7.76 0.40 % Foliage covera, 0.5-1.0 m 0.33 0.15 2.09 0.51 % Vertical coverb, < 0.5 m 29.64 2.02 44.58 1.13 % Vertical coverb, 0.5 -1.0 m 9.78 1.63 29.41 3.31
a Percentage of the occurrence of foliage within a radius of 0.1 m of the stick. b Percentage of squares at least half obscured.
86
Table 13. Number of Northern Harrier nests located on and off the Peabody Wildlife Management Area during the 2003 and 2003 breeding seasons and the fate of those nests. 2002 2003 Total Total number of nests: 27 19 46 Sinclair 10 14 24 Homestead 8 1 9 Ken Hopewell 2 1 3 Vogue 3 1 4 Riverqueen 3 2 5 Private Property off the Peabody WMA 1 0 1 Total number of successful nests (number of young fledged): 5 (15) 5 (13) 10 (28) Sinclair 2 (8) 2 (5) 4 (13) Homestead 0 1 (4) 1 (4) Ken Hopewell 2 (5) 1 (2) 3 (7) Vogue 0 1 (2) 1 (2) Riverqueen 1 (2) 0 1 (2) Private Property 0 0 0 Nest Success 18.5% 26.3% 21.7% Total number of eggs counted 116 74 190 Mean clutch size (based only on clutches known to be complete) 5.4 (21) 4.3 (13) 5.07 (34)
Total number of nestlings observed (counting all nests, including some where some eggs may not yet have hatched) 58 29 87
Hatching success (based only on nests where fate of all eggs was known) 74.4% 96.4% 84.5%
Mean brood size (based only on nests where fate of all eggs was known) 4.13 (8) 4.5 (6) 4.29 (14)
Total number of fledglings: 15 13 28 Males 1 8 9 Females 3 4 7 Unknown sex 11 1 12 Nestling success 33.4% (8) 49.5% (6) 40.3% (14)
87
Table 14. Variables permitting best discrimination between successful and predated nests of Northern Harriers on a reclaimed surface mine grassland in west-central Kentucky. Predated nests Successful nests
(N = 32) (N = 10)
Variable mean SE mean SE % Grass cover
27.03
5.85
17.00
10.96
% Shrub cover
9.38
3.40
12.50
8.37
Foliage cover at nesta, below 0.5 m
7.36
0.26
7.68
0.77
Foliage cover at nesta, 0.5 – 1 m
2.78
0.27
4.58
0.52
Foliage cover at nesta, > 1 m
0.09
0.05
0.05
0.03
% Vertical coverb, 1 – 2 m
43.20
6.37
75.47
9.71
a Percentage of the occurrence of foliage within a radius of 0.1 m of the stick. b Percentage of squares at least half obscured.
88
Table 15. Variables permitting best discrimination between nest sites of Northern Harriers and randomly-selected, unused sites on a reclaimed surface mine grassland in west-central Kentucky. Used sites Unused sites (N = 42) (N = 38) Variable mean SE mean SE Distance to nearest tree (m)
32.5
5.6
28.2
4.8
Distance to nearest water (m)
139.6
13.1
166.7
15.2
Distance to nearest shrub (m)
8.38
1.47
14.31
2.29
Number of trees < 8 cm dbh
0.75
0.32
0.87
0.37
% Tree cover
1.14
0.46
0.66
0.47
Foliage covera, 0.5 - 1 m
4.22
0.23
3.25
0.19
a Percentage of the occurrence of foliage within a radius of 0.1 m of the stick.
Table 16. Estimated area of potential habitat (open grasslands) for Northern Harriers and the density of Northern Harrier nests (km2) on various units of the Peabody Wildlife Management Area.
Unit Area (km2)
Active pairs 2002
Nest density 2002
Active pairs 2003
Nest density 2003
Nest densities for 2002-2003
combined Sinclair 11.9 6 0.50 7 0.58 0.54 Vogue 2.4 2 0.83 1 0.41 0.62 Ken Hopewell/Homestead 20.7 6 0.28 2 0.09 0.18 Riverqueen/Ken American 4.7 3 0.63 2 0.42 0.52 Nest 25/ Ken Hopewell 3.3 1 0.30 0 0 0.15 Total or Mean/km2 43 18 0.61 12 0.30 0.40
89
Appendix B. Figures.
90
Figure 1. Map of the Peabody Wildlife Management Area in Ohio and Muhlenberg counties, Kentucky
91
Figure 2. The survey route through the Peabody Wildlife Management Area and surrounding areas.
92
0
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30
40
50
60
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80
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Figure 3. Mean number of raptors observed per month during road surveys on the Peabody Wildlife Management Area, 2002 – 2003.
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Figure 4. Raptor densities on various units of the Peabody Wildlife Management Area during the winter (January - March), 2002 – 2003 (S = Sinclair, V = Vogue, H/KH = Homestead and Ken Hopewell, RQ = Riverqueen, and G = Gibraltor).
93
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Figure 5. Variation in the number of Red-tailed Hawks observed during surveys on the Peabody Wildlife Management Area, 2002 - 2003.
94
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Figure 6. Densities of Red-tailed Hawks during the winter (January - March) and summer (June - July) on various units of the Peabody Wildlife Management Area (S = Sinclair, V = Vogue, H/KH = Ken Hopewell and Homestead, RQ = Riverqueen, and G = Gibraltor).
95
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Figure 7. Variation in numbers of Northern Harriers observed during road surveys on the Peabody Wildlife Management Area, 2002 - 2003.
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Figure 8. Densities of Northern Harriers on various units of the Peabody Wildlife Management Area during the winter (January - March), 2002 – 2003 (S = Sinclair, V = Vogue, H/KH = Ken Hopewell, RQ = Riverqueen, and G = Gibraltor).
96
Figure 9. The location of a communal roost used by Northern Harriers on the Sinclair Unit (S1 and S2 intersection) of the Peabody Wildlife Management Area.
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Figure 10. Variation in numbers of American Kestrels observed during road surveys on the Peabody Wildlife Management Area, 2002 - 2003.
97
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98
Figure 12. Locations of communal roosts of Short-eared Owls on the Sinclair Unit of the Peabody Wildlife Management Area, near S3 food plot areas.
99
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0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
CR GL GS PAS RE SS UNK W WE WET
Habitat Type
Perc
ent
Non-breeding�����
Breeding
Habitat available
Figure 13. Habitats in which Red-tailed Hawks were observed during road surveys conducted during the non-breeding (October - March) and breeding seasons (April - September), 2002 - 2003 (CR = cropland, GL = tall grass, GS = short grass, PAS = pasture, RE = roadside edge, SS = scattered shrub, UNK = unknown, W = woodlot, WE = woodlot edge, and WET = wetland).
100
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����������
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0%
80.0%
90.0%
100.0%
CR GL GS RE SS UNK W WET
Habitat Type
Perc
ent
Non-breeding�������� Breeding
Habitat available
Figure 14. Habitats in which Northern Harriers were observed during road surveys conducted during the non-breeding (October - March) and breeding (April - September) seasons, 2002 - 2003 (CR = cropland, GL = tall grass, GS = short grass, RE = roadside edge, SS = scattered shrubs, UNK = unknown, W = woodlot, and WET = wetland).
101
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0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0%
80.0%
CR GL GS RE SS W WE WETHabitat Type
Perc
ent
Non-breeding�������� Breeding
Dominant Habitat
Figure 15. Habitats in which American Kestrels were observed during road surveys conducted during the non-breeding (October - March) and breeding (April - September) seasons, 2002 - 2003 (CR = cropland, GL = tall grass, GS = short grass, RE = roadside edge, SS = scattered shrubs, W = woodlot, WE = woodlot edge, and WET = wetland).
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0
20
40
60
80
100
120
140
160
1988
-89
1989
-90
1990
-91
1991
-92
1992
-93
1993
-94
1994
-95
1995
-96
1996
-97
1997
-98
1998
-99
99-2
000
2000
-01
2001
-02
2002
-03
Year
num
ber
of in
divi
dual
s
Figure 16. Numbers of Short-eared Owls observed during Paradise Christmas Bird Counts from 1988 through 2003 (based on data from Ferrell 1990-2003).
Figure 17. Count area for the Paradise Christmas Bird Count in Muhlenberg, Ohio, Butler, McLean, and Logan counties
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02
468
101214
1618
Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec
Month
Num
ber
of o
bser
vatio
ns
Figure 18. Annual variation in number of Red-shouldered Hawks observed during road surveys on the Peabody Wildlife Management Area, 2002 - 2003.
0
5
10
15
20
25
30
CR GL GS RE SS W WE WET
Habitat type
Num
ber
of o
bser
vatio
ns
Figure 19. Habitats in which Red-shouldered Hawks (N = 60) were observed during road surveys in the Peabody Wildlife Management Area, 2002 – 2003 (CR = cropland, GL = tall grass, GS = short grass, RE = roadside edge, SS = scattered shrubs, W = woodlot, WE = woodlot edge, and WET = wetland).
104
0
5
10
15
20
25
30
GL GS RE SS
Habitat type
Num
ber
of o
bser
vatio
ns
Figure 20. Habitats in which Rough-legged Hawks (N = 31) were observed during road surveys on the Peabody Wildlife Management Area, 2002 – 2003 (GL = tall grass, GS = short grass, RE = roadside edge, and SS = scattered shrubs).
0
2
4
6
8
10
12
DF HF HH PH PR S
Behavior
Num
ber
of o
bser
vatio
ns
Figure 21. Behavior of Rough-legged Hawks (N = 31) observed during road surveys on the Peabody Wildlife Management Area, 2002 – 2003 (DF = direct flight, HF = hunting in flight, HH = hover hunting, PH = perch hunting, PR = perch resting, and S = soaring).
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0
0.2
0.4
0.6
0.8
1
1.2
1988
-89
1989
-90
1990
-91
1991
-92
1992
-93
1993
-94
1994
-95
1995
-96
1996
-97
1997
-98
1998
-99
99-2
000
2000
-01
2001
-02
2002
-03
Year
Indi
vidu
als p
er h
our
Figure 22. Number of Rough-legged Hawks per party hour observed during the Paradise Christmas Bird Count from 1988 – 2003 (Ferrell 1990-2003).
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0.0%
10.0%
20.0%
30.0%
40.0%
HP HVP SP TD UNK
Attack type
Perc
ent
% Used����% Successful
Figure 23. Proportion of types and success rates of attacks (N = 183) used by Northern Harriers on the Peabody Wildlife Management Area (HP = hook pounce, HVP = hover pounce, SP = straight pounce, TD = touchdown, and UNK = unknown).
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0.0%
10.0%
20.0%
30.0%
40.0%
HP HVP SP TD
Attack type
Perc
ent
% Used����
% Successful
Figure 24. Proportion of types and success rates of attacks (N = 128) used by Short-eared Owls on the Peabody Wildlife Management Area (HP = hook pounce, HVP = hover pounce, SP = straight pounce, and TD = touchdown).
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Figure 25. Estimated home range of an adult male Northern Harrier on the Ken Hopewell Unit of the Peabody Wildlife Management Area, Ohio County, KY.
108
Figure 26. Estimated area of potential habitat (outlined in black) for breeding Northern Harriers during the 2002 and 2003 breeding seasons on the Sinclair Unit of the Peabody Wildlife Management Area, Muhlenberg County, Kentucky (11.9 km2; white circles indicate 2002 nests and black triangles 2003 nests).
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0
2
4
6
8
10
12
14
16
incubation nestling
Stage lost
num
ber
of n
ests
2002����
2003
Figure 27. The stage during nesting when nests of Northern Harriers on the Peabody Wildlife Management Area were lost to predators.
0
5
10
15
20
25
black catt dogb fesc indcurr ironw ser swpe swit
Vegetation Type
Num
ber
of n
ests
Figure 28. Dominant vegetation at nests of Northern Harrier nests (N = 44) on the Peabody Wildlife Management Area, 2002 – 2003 (black = blackberry, catt = cattail, dogb = dogbane, fesc = fescue, indcurr = indian current, ironw = ironweed, ser = sericea, swpe = sweet pea, and swit = switchgrass).
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0
2
4
6
8
10
12
14
2002 2003
Year
num
ber
of n
ests
Non-native����
Native
Figure 29. Use of exotic and native vegetation by Northern Harriers on the Peabody Wildlife Management Area, 2002 - 2003.
Figure 30. Location of Northern Harrier nests on the Sinclair Unit of the Peabody Wildlife Management Area in 2002 and 2003 (white circles indicate 2002 nests and black triangles 2003 nests).
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Appendix C. Detailed Description of the Road Survey Route.
From Beaver Dam (starting point) to Vogue (end point) (see Tables C-1, C-2, and C-3):
1. Applehouse Rd. (between NAPA Auto Parts and the BP station). Exit 75 off the Western Kentucky Parkway. The NAPA Auto Parts parking lot is a good spot for weather observations, but walk to grassy area to take temperature reading because heat may be given off by the parking lot.
2. Take a left onto 369 south. 3. Right onto Wysox Rd. (gravel road). 4. Wysox Road becomes Pond Run Rd. 5. Pond Run Rd. turns into KY 92-1245. 6. KY 92-1245 ends at 62. Take a left. 7. Go over bridge (Green River). 8. First left after bridge is Rockport Paradise Rd. (no sign present, and a very sharp
turn) 9. Follow Rockport Paradise Rd. (some sharp turns on this road) until 176 (Paradise
power plant). 10. Turn left onto 176 (sometimes called the TVA Circle Rd.). 11. Turn right and (go through two stop signs) onto gravel road (Riverside Church
Rd; no marker present). 12. Go about 0.5 mile and take a right onto S2 (second right after the two haul roads). 13. Follow S2 up the hill to S1. 14. Take a right onto S1 (sharp turn). 15. Take a left onto 176. 16. Survey discontinues at intersection of 431 and 176. 17. Go north on 431 to the Western Kentucky Parkway. 18. Go west on Western Kentucky Parkway to exit 53 (181). 19. At ramp, the survey continues. 20. Take a left onto 181 north. 21. Take a left after railroad tracks (about 20 m) onto RQ 12 (no longer RQ 12 now). 22. On RQ 12 or Ken American Road, go west to big power lines (see map). 23. When parallel to lines and going up the hill take that left. 24. Ends at Cedar Grove Cemetery Rd (paved road). 25. Take left onto Cedar Grove Cemetery Rd. 26. Take a left at RQ 9 (first left after going under railroad tracks) 27. Follow RQ 9 until it ends. 28. Take a left onto unmarked gravel road (RQ 9 or Doodle Road - refer to Peabody
WMA map). 29. Take a right onto Cedar Grove Cemetery Rd. 30. Take a right onto RQ 1 (first 4-way intersection; see Peabody WMA map).
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31. Stay on RQ 1 until it ends. (Careful, this road forks, stay right - See Peabody WMA map).
32. Take a right onto RQ Haul Rd. 33. Go to 175 crossing (caution), go into Vogue-V-6. 34. Follow V-6. 35. Take a left onto V-7 (sign may be obscured by vegetation). 36. Take first right onto unmarked gravel road (I called it the Vogue Hill Rd.), no
gas-line or gas pumpstation roads are included as roads! 37. Follow Vogue Hill Rd. to crest, just past the sumac. Stop here. This is the end
point of the survey route.
Table C-1. Units of the Peabody WMA and odometer readings (starting at Beaver Dam and stopping in the Vogue Unit).
Unit Odometer Homestead and Ken Hopewell 6.5 - 15.6 Gibraltor 22.4 - 24.0 Sinclair 27.8 - 33.8 Riverqueen 49.5 - 56.8 Vogue 56.7 - 59.2
From the Vogue Unit to Beaver Dam:
1. Starting point is Vogue Hill Rd., at the crest of hill. 2. Go down hill and take a left at S 7. 3. Take a right at S 6. 4. At 175 crossing, go straight onto RQ Haul Rd. 5. Take a left onto S 1 (there is a sign there) 6. Take a left onto Cedar Grove Cemetery Rd. (just past lake on left; 4-way
intersection). 7. Take a left onto S 9 or Doodle Rd. 8. Take a right onto S 9. (shot up sign there). 9. Take a left onto Cedar Grove Cemetery Rd. 10. Take a right onto RQ 19 or Ken American Rd. 11. Take a right onto 181 south. 12. Go under Western Kentucky Parkway and get on ramp (go east). Survey count
discontinues. 13. Go to Central City exit, and then get on 431 south to Drakesboro. 14. At Drakesboro, take a left onto 176. Survey continues here. 15. Take a right onto S 1 (coal trucks get on here too) 16. Take a left onto S 2. 17. Take a left onto Riverside Church Rd. Go through two stop signs. 18. Take a left onto 176 (or TVA Circle Road; it’s a paved road).
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19. Take a right onto Rockport Paradise Rd (no marker present). 20. Take a right onto 62. 21. Take a right onto KY 92-1245. 22. KY 92-1245 turns into Pond Run Rd (gravel road). 23. Take a left at Wysox Rd. 24. Take a left onto 369. 25. Take a right onto Applehouse Rd. 26. End survey at parking lot of NAPA Auto Parts.
Table C-2. Units of the Peabody WMA and odometer readings (Vogue Unit to Beaver Dam).
Unit Odometer Vogue 0.0 - 2.4 Riverqueen 2.5 - 9.8 Sinclair 25.2 - 31.2 Gibraltor 35.0 - 36.6 Homestead and Ken Hopewell 43.4 - 52.5
Table C-3. Digital orthophotographs (7.5 min, quadrangle quarters) that include portions of the Peabody Wildlife Management Area (KYGEONET 2000).
P22SW Q22NW P22NE P22NW Q21NW P21SE P21NE P23SW P20SW Q21NE P23NW P19SW Q22NW P22SE P19SE
Illegal shooting
Although public opinions about raptors have changed since the early 1900s, the
illegal shooting of raptors still occurs. On 18 October 2003, an injured Red-tailed Hawk
(immature male) was found on the Sinclair Unit of the Peabody WMA by my field
assistant, Matt Giovanni. The bird was subsequently taken to Raptor Rehab of Kentucky
114
in Louisville, Kentucky (Operated by Eileen Wicker). X-rays revealed that the bird had
been shot in the right wing. The bird was successfully treated, rehabilitated, and released
near the Homestead Unit on 24 March 2003. Raptors are protected under the Migratory
Bird Treaty Act of 1918.
Appendix D. General Life History Observations.
Breeding biology
Northern Harrier nests were initiated (egg-laying) on the Peabody WMA from
April to June (earliest was 1 April and the latest was 20 June). Observations of male
Northern Harriers performing courtship flights or 'sky dances' were made between 8
February - 23 June in 2002 and 2003. Thompson-Hanson (1984) reported that sky
dancing began in late February (24 February), but my observations suggest that courtship
flights may begin earlier. In addition, an adult female Northern Harrier was observed sky
dancing on the Riverqueen Unit on 26 April 2003. An adult male, sky dancing nearby
(nest 11 and 39 area), apparently observed the female displaying and flew directly to the
female who had perched on a post shortly after displaying. They immediately copulated.
Females have been reported sky dancing (Simmons et al. 1987), but little is known about
the possible functions of the female sky dance. However, my observation suggests that at
least one possible function of the female sky dance is to solicit a copulation.
Other interesting behaviors were also observed during the pair-bonding and nest-
building periods. Toland (1986) described a 'leap frog' behavior in which female and
male Northern Harriers took turns leaping into thick vegetation near a future nest-site.
During my study, male harriers were frequently observed flying or diving (feet first) into
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dense thickets of blackberries, possibly attempting to clear an area for a nest. In addition,
paired harriers were observed chasing each other and switching perches. One such pair
was observed in a wet, forested area on the Riverqueen Unit in May 2002. The area was
subsequently searched, but no nest was located. Northern Harriers have been reported to
nest in forested habitats (Watson 1977). Furthermore, the female at nest 22 took food
from her nest and apparently cached food several times. This has been reported by
MacWhirter and Bildstein (1996)
Watson (1977) suggested that, after losing a nest, male Northern Harriers may
begin building a new platform without a female present ('frustration' behavior), and such
behavior was observed on the Riverqueen and Sinclair units. The male harrier at nest 39
(Riverqueen Unit) was observed carrying nesting material one week after its first nest
was lost to predation (27 May 2003). This male hovered over certain areas, dropped
nesting material, and then grabbed more material. No female was observed in the area.
Similarly, on the Sinclair Unit, nest 29 was depredated (5 June 2003), but the male
remained in the area for another 10 days. During this time, the male was observed sky
dancing and 'leaping' into a blackberry thicket, possibly attempting to create a nest
platform. Again, no female was observed in the area.
Disturbance
Although most literature indicates a preference of 'undisturbed areas' by Northern
Harriers, some individuals in my study showed remarkable tolerance to human
disturbance. Several Northern Harrier nests were located within 100 m of roads where
there was much traffic, including large coal trucks (80 tons). Thompson-Hanson (1984)
also reported that Northern Harriers appeared to tolerate human activity. As long as
116
117
disturbance occurs regularly, harriers seem unaffected. One extraordinary case of
disturbance was observed on the Riverqueen Unit. Nest 28 was located in a small cattail
marsh, approximately 170.5 m from the nearest road. On 26 April 2003, the nest was
checked for activity because the female had been observed building a nest on 17 April.
Shortly before arriving, a male and female harrier were observed in flight near the nest
area and, once at the nest site, I discovered a dog exhibition in progress. A tent was
located within 150 m of the nest along with a crowd of people (including several shooting
blanks) and hunting dogs. One group of men and their dogs were within 20 m of the
harrier nest. Surprisingly, a check of the nest on the next day revealed an incubating
female.