deer and cattle foraging strategies under different

DEER AND CATTLE FORAGING STRATEGIES UNDER DIFFERENT

GRAZING SYSTEMS AND STOCKING RATES

by

ISAAC M. ORTEGA, B.S., M.S.

A DISSERTATION

IN

WILDLIFE SCIENCE

Submitted to the Graduate Faculty of Texas Tech University in

Partial Fulfillment of the Requirements for

the Degree of

DOCTOR OF PHILOSOPHY

Approved

Accepted

December, 1991

f

T3 , I ^ ^ ' ACKNOWLEDGEMENTS

l\/o 1^3

The study was supported by the Rob and Bessie Welder

Wildlife Foundation and the Department of Range and Wildlife

Management, Texas Tech University. I am indebted to many

individuals who offered their help, guidance, and friendship.

I would to thank Dr. James G. Teer for providing me a Welder

fellowship for five years. I am very thankful to Dr. Fred C.

Bryant who went the extra mile to obtain funds for this

project. I am thankful to Dr. Henry Wright for providing me

with funding for the last part of my degree program.

I would like to express my appreciation to my committee

members for their patience and taking time in guiding me

through the long process of the doctoral degree. These

include Dr. Fred Bryant, Chairman, Dr. Bill Dahl, Dr. Stephen

Demarais, Dr. Lynn Drawe, Dr. Ernest Fish, and Dr. Kent

Rylander.

Dr. Sergio Soltero-Gardea was a key person in the

completion of this project. As he put it ^ we shared not only

the logistic problems, but also chiggers and ticks together."

Although there were some rough times, we overcame them and

continued working hard to make this project a success. Thank

you, Sergio. I would also like to thank Dr. Lynn Drawe who

provided me with his friendship, constant help in field

activities, advice in the research work, and for listening to

my complaints. Mr. James Cox provided us with all his

1 1

imagination to solve any type of problem related to the field

activities. He was the master of building fences and pens,

and the handling of the cattle. I would like to thank Mr.

Baldomar Martinez, who also was extremely helpful in the

building of fences and pens, and the cattle handling.

I had the pleasure to work with many fine assistants

such as Mr. Lance Perry, Bruce Rust, Denisse Rufino, Cynthia

Simpkins, and Charles Forester. Thank you all.

Thanks also go to my good friend Dr. Tariq Qureshi. He

insured the health of the deer, esophageally fistulated

several steers, and provided enlightened conversation.

Thanks to fellow students Collen McDonough, Janet Rasmussen,

Kevin Theather, and many others for providing us with their

assistance and their friendship while at the Refuge. Thanks

to Dr. David Hirth, from Vermont University, who helped me to

better understand, the behavior of white-tailed deer. I

would like to thank the Welder personnel Gene, LaFaye, Mrs.

Weir, Vaunda, the Garzas, Beto, and Jessie for the many

little things they did for us.

In the tedious work of reading microhistological slides,

I would like to thank Gretchen Scott for training my two

excellent slide readers: Isabel Berger and Danielle Van Noy.

Thanks go to Andrea Ernst for entering data in the computer.

Special thanks go to Dr. David Haukos and Dr. David Wester

for helping me to better understand the numbers I collected

1 1 1

at Welder. I would like to express my appreciation to Dr.

Manuel Martinez from the Mathematics Department for helping

me to understand discriminant analysis. Thank you Rick

Relyea for let me use your fast Mac SE/30.

I would like to express special gratitude to Dr. Fred C.

Bryant for having confidence in the way I worked, for solving

any bureaucratic problem that arose, and for his guidance and

friendship throughout my degree.

A very important person who helped me every step of the

way in conquering this degree was my wife, Isabel. She was

my faithful field assistant while collecting data with the

deer. Although her fear of snakes was immense she did not

hesitate in helping me to herd the deer to and from the

treatment pastures. She allowed me to raise fawns inside of

the house and helped me in raising them. On campus, she

worked in the lab and on the computer. As Dr. Bryant

mentioned one time, 'Isabel deserves a Ph.D. for all the work

that she has done during this project," I agree. A couple of

little boys helped me in many ways, these are my two sons

Morty, Jr. and Ivan. They were a key factor in making my

fawns end up as very tame deer. Thanks to my parents, Eladio

and Nora; even from a great distance, they believed in me all

these years.

This work is dedicated to Isabel, Morty Jr., and Ivan.

IV

TABLE OF CONTENTS

ACKNOWLEDGEMENTS ii

ABSTRACT vii

LIST OF TABLES ix

LIST OF FIGURES xiv

CHAPTER

I. INTRODUCTION 1

Literature Cited 5

II. CONTRAST OF ESOPHAGEAL FISTULA VERSUS BITE-COUNT TECHNIQUES TO DETERMINE CATTLE DIETS 8

Introduction 8

Materials and Methods 9

Results 11

Discussion 20

Conclusions 21

Literature Cited 23

III. FOOD HABITS AND DIETARY OVERLAP OF CATTLE AND DEER UNDER DIFFERENT GRAZING SYSTEMS AND STOCKING RATES 25

Introduction 25

Study Site 26

Methods 2 8

Grazing Treatments 28

Deer Diets 30

Cattle Diets 31

Vegetation Measurements 32

V

Data Analysis 33

Results 35

Study Area Homogeneity and

Floral Changes 35

Cattle and Deer Diets 51

Dietary Overlap 69

Discussion 69

Floral Changes 69

Cattle and Deer diets 71

Management Implications 78

Literature Cited 82

IV. FORAGING BEHAVIOR OF TRACTABLE

WHITE-TAILED DEER 8 9

Introduction 89

Methods 91

Predictions 93

Results and Discussion 93

Conclusions 102

Literature Cited 104

APPENDICES

A. Plant species common and scientific names ... 106

B. Analysis of variance tables Ill

C. Formulae and raw data of cattle and deer food habits under different grazing strategies 115

D. Analysis of variance tables of foraging behavior of tractable white-tailed deer 149

VI

ABSTRACT

The purpose of this research was to determine the

foraging strategies of deer and cattle under continuous and

short-duration grazing at heavy and moderate stocking rates.

The study was conducted from October 1987 through July 1989

at the Welder Wildlife Refuge, Sinton, San Patricio County,

Texas. From tame white-tailed deer, I obtained food habits

data by direct observation. The esophageal fistula technique

was used to determine cattle diets. To understand how

different techniques might affect diet estimates for cattle,

I compared the esophageal fistula and direct observation

techniques using gentle, tractable cattle. I concluded that

for the Texas Coastal Bend, an area with highly diverse plant

communities, direct observation is not as reliable a

technique as the esophageal fistula. These techniques were

different in determining the use of forage classes and plant

species in cattle diets. The bite-count technique may be

acceptable if analyses are limited to only those plant

species making up >2% of the diet.

Homogeneity of the vegetation community of the study

pastures was not affected by the grazing treatments. However,

the drought of the second year produced some floral changes.

Through use of canonical discriminant analysis, diets of

deer and cattle were found to be distinct from each other in

every treatment throughout the sampling period. Differences

vii

were related to forage classes used by the animal species.

Overall, deer used mostly forbs (72%) while cattle primarily

used grasses (60%) and forbs (39%). The forbs Oxalls

dinellii, Ruellia nudiflora, and Desmanthus virgatus, and the

grasses Buchloe dactyloides, Tridens congestus, and Stipa

leucotricha were the species that separated deer and cattle

diets. Deer were most sensitive to the vegetation conditions

within each treatment during the summer months (May through

September) and the second winter which was affected by the

drought. During these periods deer selected different diets

across all treatments. Deer were the least sensitive to the

grazing treatments during spring. Their diets were the same

across all treatments.

The highest diet overlap (range = 43-64%) between deer

and cattle occurred in Winter 1 and Spring 1, when deer and

cattle were consuming Ambrosia psilostachya. Geranium

carolinianum, Oenothera speciosa, O. dillenii^ and Ratibida

columnaris. During the second year, significant overlap

occurred only on pastures heavily stocked by cattle.

Information on deer foraging behavior, which included

grazing time, bites per minute, and distance traveled, was

collected under the different treatments. Predictions such

as an inverse relationship between search time and grazing

time (r = -0.91), or the direct relationship between search

time and the distance traveled (r = 0.92), were confirmed for

white-tailed deer.

• I f

Vlll

LIST OF TABLES

2.1. Number of plant species detected monthly using the bite-count (BC) and the esophageal-fistula (EF) methods 15

2.2. Relative frequency of plant species in monthly cattle diets using the bite-count (BC) and the esophageal-fistula (EF) methods 16

3.1. Floral diversity index for the different grazing treatments during April 1986, 1988, and 1989 at the Welder Wildlife Refuge 37

3.2. Fall availability (percent frequency) of plant species in the treatment pastures at the Welder Wildlife Refuge 38

3.3. Winter availability (percent frequency) of plant species in the treatment pastures at the Welder Wildlife Refuge 40

3.4. Spring availability (percent frequency) of plant species in the treatment pastures at the Welder Wildlife Refuge 42

3.5. Summer availability (percent frequency) of plant species in the treatment pastures at the Welder Wildlife Refuge 44

3.6. Availability (percent frequency) of the five species most frequently used by cattle and deer under different grazing treatments across all seasons and years 1987-1989 at the Welder Wildlife Refuge 46

3.7. Browse availability (percent frequency) in the treatment pastures at the Welder Wildlife Refuge 52

3.8. Levels of significance of F-values for the discriminant analysis used to separate cattle and deer diets throughout the study periods at the Welder Wildlife Refuge 54

ix

3.9. Levels of significance of F-values for the discriminant analysis used to contrast cattle/cattle and deer/deer diets under different treatments throughout the study period at the Welder Wildlife Refuge 55

3.10. Forage classes (dietary percent) used by deer and cattle throughout the study, 1987-1989, at the Welder Wildlife Refuge 56

3.11. Forage classes (dietary percent) used by cattle and deer as influenced by grazing systems and stocking rates at the Welder Wildlife Refuge 58

4.1. Foraging behavior of white-tailed deer under different grazing treatments averaged across all seasons 94

4.2. Seasonal foraging behavior of white-tailed deer under different grazing treatments 96

4.3. Seasonal travel distance, search time, and grazing time of white-tailed deer across grazing treatments .•" 97

A.l. Common and scientific names of forbs used by deer and cattle at the Welder Wildlife Refuge, Sinton, TX, 1987-1989 107

A. 2. Common and scientific names of grasses and sedges used by deer and cattle at the Welder Wildlife Refuge, Sinton, TX, 1987-1989 109

A. 3. Common and scientific names of browse species used by deer and cattle at the Welder Wildlife Refuge, Sinton, TX, 1987-1989 110

B.l Analysis of variance for dietary forbs when comparing bite-count versus esophageal fistula 112

B.2 Analysis of variance for dietary grasses when comparing bite-count versus esophageal fistula 113

X

B.3 Analysis of variance for dietary browse when comparing bite-count versus esophageal fistula 114

C.l. Formulae for F ratios for the Mahalanobis

distance between each pair of groups 116

C.2. Formulae for Morosita-Horn similarity index ,. 117

C.3. Analysis of variance for availability of Stipa leucotricha 118

C.4. Analysis of variance for availability of Buchloe dactyloides 119

C.5. Analysis of variance for availability of Tidens congestus 120

C.6. Analysis of variance for availability of Lesquerella lindheimeri 121

C.7. Analysis of variance for availability of Ratibida columnaris 122

C.8. Analysis of variance for availability of Oxalis dillenii 123

C.9. Analysis of variance for availability of Commelina erecta 124

C.IO. Analysis of variance for availability of Phyrrhopappus multicaulis 125

C.ll. Analysis of variance for availability of Geranium carolinianum 12 6

C.12. Analysis of variance for forbs used by cattle under the influence of grazing systems and stocking rates throughout the study period 127

C.13. Analysis of variance for grasses/sedges used by cattle under the influence of grazing systems and stocking rates throughout the study period 128

XI

C.14. Analysis of variance for browse used by cattle under the influence of grazing systems and stocking rates throughout the study period 12 9

C.15. Analysis of variance for forbs used by deer under the influence of grazing systems and stocking rates throughout the study period 130

C.16. Analysis of variance for grasses/sedges used by deer under the influence of grazing systems and stocking rates throughout the study period 131

C.17. Analysis of variance for browse used by deer under the influence of grazing systems and stocking rates throughout the study period 132

C.18. Cattle and deer diet composition (%) under continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Fall 1 133

C.19. Cattle and deer diet composition (%) under continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Winter 1 135

C.20. Cattle and deer diet composition (%) under continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Spring 1 137

C.21. Cattle and deer diet composition (%) under continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Summer 1 139

Xll

C.22. Cattle and deer diet composition (%) under continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Fall 2 141

C.23. Cattle and deer diet composition (%) under continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Winter 2 143

C.24. Cattle and deer diet composition (%) under continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Spring 2 145

C.25. Cattle and deer diet composition (%) under continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Summer 2 147

D.l. Analysis of variance for the foraging behavior of tractable deer, using search time as dependent variable 150

D.2. Analysis of variance for the foraging behavior of tractable deer, using grazing time as dependent variable 151

D.3. Analysis of variance for the foraging behavior of tractable deer, using travel distance as dependent variable 152

Xlll

LIST OF FIGURES

2.1. Cattle diets as determined by the bite-count and the esophageal-fistula methods for different forage classes 12

2.2. Monthly cattle diets by forage class as determined by the bite-count and the esophageal-fistula techniques 13

3.1. Study area (a) Texas location of the study site and (b) design and distribution of treatment pastures and replications 29

3.2. Seasonal changes in the availability (percent frequency) of grasses most heavily used by deer and cattle 47

3.3. Seasonal changes in the availability (percent frequency) of forbs most heavily used by deer and cattle 4 9

3.4. Seasonal changes in the availability (percent frequency) of forbs most heavily used by deer and cattle 50

3.5. Plot of canonical discriminant centroids of deer and cattle diets for each grazing treatment pooled across seasons 53

3.6. Plot of canonical discriminant centroids for first year of deer and cattle diets for each grazing treatment 59

3.7. Plot of canonical discriminant centroids for second year of deer and cattle diets for each grazing treatment 60

3.8. Use of forbs by deer and cattle under continuous (CG) and short-duration (SD) grazing systems; and heavy and moderate stocking rates during 1987-1989 at the Welder Wildlife Refuge 62

3.9. Use of grasses by deer and cattle under continuous (CG) and short-duration (SD) grazing systems; and heavy and moderate stocking rates during 1987-1989 at the Welder Wildlife Refuge 63

XIV

3.10. Use of browse by deer and cattle under continuous (CG) and short-duration (SD) grazing systems; and heavy and moderate stocking rates during 1987-1989 at the Welder Wildlife Refuge 64

3.11. Dietary overlap between cattle and deer under continuous (C) and short-duration (S) grazing and heavy (H) and moderate (M) stocking rates 70

4.1. Seasonal diversity indices (1/d) for (a) vegetation of different treatments and (b) deer diets 98

4.2. Plot of regression lines for search time (min.) versus (a) grazing time (bites/min.), (b) travel distance (m), (c) diet diversity and (d) forage diversity (1/d) for white-tailed deer across all different grazing treatments 100

4.3. Plot of regression lines for (a) search time (min.) versus forage diversity (1/d); grazing time (bites/min) versus (b) travel distance (m), (c) diet diversity and (d) forage diversity (1/d) for white-tailed deer across all different grazing treatments 101

XV

CHAPTER I

INTRODUCTION

Rangeland management for optimum production of livestock

and large herbivores requires an understanding of their

behavior, population dynamics, and food habits (Chamrad et

al. 1979) . Many researchers have studied the composition of

diets selected by wild and domestic ungulates (Hanley 1982) .

In Texas, numerous studies exist concerning white-tailed deer

{Odocoileus virginianus), livestock, and exotics diets to

better understand their interrelationships (McMahan 1964,

Drawe 1967, Chamrad and Box 1968, Bryant et al. 1979, Pitts

and Bryant 1987, Jackley 1991). These studies have addressed

questions asked both by biologists and livestock producers

who are interested in knowledge which results in better

management of domestic, wild, and exotic ungulates. Today,

producers have special interest in the profits that can be

obtained from wildlife harvesting, especially white-tailed

deer (Bryant and Smith 1987, McCullough 1987, Glimp 1988,

Bryant 1989, Loomis et al. 1991).

Short-duration grazing (SD) was introduced in the USA as

an alternative grazing practice that reportedly allows the

rancher to increase stocking rates, therefore increasing his

economic return while improving range condition (Goodloe

1969, Savory and Parsons 1980). This grazing practice

remains controversial because (a) there are still doubts that

SD improves animal distribution, (b) some studies have

suggested that SD resulted in lower animal performance, (c)

that only a 10 to 20% stocking rate increase should be

considered, not a 100% increase as suggested by the principal

proponents of this grazing practice, (d) studies have shown

no increase of forage (grasses or forbs) standing crop, and

(e) of excessive economic input and management intensity

(Heitschmidt and Walker 1983, Dickerson 1985, Weltz and Wood

1986, Nelson et al. 1989, Bryant et al. 1989, Guthery et al.

1990, Ralphs et al. 1990). Some researchers have

investigated the impact of this system on wildlife (Bareiss

1985, Hyde 1987, Cohen et al. 1989).

Short-duration grazing is a method that is not

universally applicable. Modifications may need to be

implemented to obtain some of its benefits. These may be

related to capability of the land and/or the involvement and

commitment of the rancher to intensive cattle management

(Malecheck and Dwyer 1983, Quigley 1987). Establishment of

the number of paddocks, stocking rate, duration of grazing,

and rest will vary according to the weather patterns of the

area. However, there is a consensus that doubling the

stocking rate as proposed by Savory and Parsons (1980) is not

feasible in arid and semiarid regions (Bryant et al. 1989).

Skovlin (1987) found that in southern Africa, severe range

degradation has resulted where stocking rates have been

doubled. Wildlife studies have shown that when SD has been

compared to continuous grazing (CG), no major adverse impact

has been recorded for game species such as quail and deer

(Bareiss 1985, Cohen et al. 1989, Guthery et al. 1990).

However, SD under a heavy stocking rate increased bird

species diversity which was attributed to a combination of

plant species composition and higher variance in structural

measures (Swanson 1988) .

Constraints for researchers working on grazing systems,

include the difficulty and expense in establishing replicated

experiments, the inability to examine stocking rate, prior

grazing history, and parameters which are difficult to

measure on animals or the environment (i.e., some types of

behavior or vegetation availability). Working with wild

species adds yet another constraint that relates to the

difficulty in obtaining accurate data. Such constraints have

slowed the pace of research concerning grazing systems.

Because of their economic and ecological importance,

there is a need to determine the impact of SD on white-tailed

deer on the Texas Coastal Bend. This study was an effort to

improve such knowledge. To avoid high expense, I conducted

research in a design which simulated, yet replicated both

continuous and short-duration grazing treatments. I included

a stocking rate commonly used throughout the region (1 AU/4.9

ha/yr), and a stocking rate at twice that level (1 AU/ 2.4

ha/yr). To obtain data on foraging strategies, I used

esophageally fistulated steers and tame deer. Since few

studies compare the techniques of esophageally fistulated

animals and direct observation (Free et al. 1971), I

conducted such a study using cattle. In Chapter II, I

present the results of this study. Chapter III explains the

effects of grazing systems and stocking rates on deer and

cattle diets, along with the possible overlap of their diets

that these treatments may inflict. Finally, Chapter IV deals

exclusively with the foraging behavior of white-tailed deer

under these grazing treatments.

Literature Cited

Bareiss, L.J. 1985. Response of bobwhites to short duration and continuous grazing in south Texas. M.S. Thesis. Texas Tech Univ. Lubbock, TX. 37 pp.

Bryant, F.C. 1989. Economic implications of wildlife. Proc. Western S e c , Amer. Soc. Anim. Sci. 40:500-502.

Bryant, F.C. and L.M. Smith. 1987. The role of wildlife as an economic input into a farming or ranching operation. Pp: 95-98. In: J.E. Mitchell (ed.) Impacts of the Conservation Reserve Program in the Great Plains. USDA Tech.Rep. RM-158, Rocky Mt. For. and Range Exp.Sta., Fort Collins, CO.

Bryant, F.C, B.E. Dahl, R.D. Pettit, and C M . Britton. 1989. Does short-duration grazing work in arid and semiarid regions? J. Soil and Water Cons. 44:290-296.

Bryant, F.C, M.M. Kothmann, and L.B. Merrill. 1979. Diets of sheep. Angora goats, Spanish goats and white-tailed deer under excellent range conditions. J. Range Manage. 32:412-417.

Chamrad, A.D., B.E. Dahl, J.G. Kie, and D.L. Drawe. 1979. Deer food habits in south Texas - status, needs and role in resource management. Proc. Welder Wildl. Found. 1:133-142.

Chamrad, A.D. and T.W. Box. 1968. Food habits of white tailed deer in south Texas. J. Range Manage. 21:158-164.

Cohen, W.E., D.L. Drawe, F.C. Bryant, and L.C Bradley. 1989. Observations on white-tailed deer and habitat response to livestock grazing in South Texas. J. Range Manage. 42:361-365.

Dickerson, R.L. 1985. Short duration grazing on Sand Shinnery oak range. M.S. Texas Tech Univ. Lubbock, TX. 88 pp.

Drawe, D.L. 1967. Forage preferences of deer and cattle on the Welder Wildlife Refuge. M.S. Thesis Texas Tech. Coll. Lubbock, TX, 75 pp.

Free, J.C, P.L. Sims, and R.M. Hansen. 1971. Methods of estimating dry-weight composition in diets of steers. J. Anim. Sci. 32:1003-1008

Glimp, H.A. 1988. Multi-species grazing and marketing. Rangelands. 10:275-278.

Goodloe, S. 1969. Short duration grazing in Rhodesia. J. Wildl. Manage. 22:369-373.

Guthery, F.S., CA. DeYoung, F.C. Bryant, and D.L. Drawe. 1990. Using short duration grazing to accomplish wildlife habitat objectives. Pp: 41-55. In: K.E. Severson (ed.) Can livestock be used as a tool to enhance wildlife habitat? USDA Forest Serv. Tech.Rep. RM-194. 123 pp.

Hanley, T.A. 1982. The nutritional basis for food selection by ungulates. J. Range Manage. 35:14 6-151.

Heitschmidt, R.K. and J. Walker. 1983. Short duration grazing and the Savory grazing method in perspective. Rangelands. 5:147-150.

Hyde, K.J. 1987. Effects of short duration grazing on white-tailed deer. M.S. Thesis. Texas A&I Univ. Kingsville, TX. 89 pp.

Jackley, J.J. 1991. Dietary overlap among axis, fallow, sika, and white-tailed deer in the Edwards Plateau Region of Texas. M.S. Thesis. Texas Tech Univ. Lubbock, TX. 189 pp.

Loomis, J.B., E.R. Loft, D.R. Updike, and J.G. Kie. 1991. Cattle-deer interactions in the Sierra Nevada: A bioeconomic approach. J. Range.Manage. 44:395-399.

Malecheck, J.C. and D.D. Dwyer. 1983. Short duration grazing. Utah Science. Summer: 32-37.

McCullough, D.R. 1987. The theory and management of Odocoileus populations. Pp: 535-549. In: CM. Wemmer (ed.) Biology and management of Cervidae. Research Symposia of the National Parks. Smithsonian Institution Press. Wash. D.C 577 pp.

McMahan, C A . 1964. Comparative food habits of deer and three classes of livestock. J. Wildl. Manage. 28:798-808.

Nelson, M.L., J.W. Finley, D.L. Scarnecchia, and S.M. Parish. 1989. Diet and forage quality of intermediate wheatgrass managed under continuous and short-duration grazing. J. Wildl. Manage. 42:474-479.

7 Pitts, J.S. and F.C. Bryant. 1987. Steer and vegetation

response to short duration and continuous grazing. J. Range Manage. 40:386-389.

Quigley, T.M. 1987. Short-duration grazing: an economic perspective. Rangelands. 9:173-175.

Ralphs, M.H., M.M. Kothmann, and CA. Taylor. 1990. Vegetation response to increased stocking rates in short-duration grazing. J. Range Manage. 43:104-108.

Savory, A. and S. Parsons. 1980. Ecological principles of short duration grazing. Beef Cattle Sci. Handbook. Agr. Serv. Found., Clovis, CA. 17:209-214.

Skovlin, J. 1987. Southern Africa's experience with intensive short duration grazing. Rangelands. 9:162-167.

Swanson, D.W. 1988. Effects of livestock grazing systems on grassland birds in south Texas. M.S. Thesis. Texas A&M Univ. College Station, TX. 50 pp.

Weltz, M. and M.K. Wood. 1986. Short duration grazing in central New Mexico: effects on infiltration rates. J. Range Manage. 36:365-368.

CHAPTER II

CONTRAST OF ESOPHAGEAL FISTULA VERSUS

BITE-COUNT TECHNIQUES TO DETERMINE

CATTLE DIETS

Introduct-ion

Techniques such as fecal analysis, forage utilization,

stomach analysis, esophageal and rumen fistulae, and direct

observation have been used to determine diets of free-ranging

ungulates (Holecheck et al. 1982). Among these techniques,

the most accurate method to determine food habits of

ungulates is the esophageal fistula (Mclnnis 1976, Mclnnis et

al. 1983) . This technique has been extensively used to

determine food habits of livestock since first described by

Torrell (1954), but has not been widely used with wild

ungulates (Kessler et al. 1981). The stress involved when

using semi-tame animals limits its efficacy (Short 1962,

Veteto et al. 1972). Direct observation (bite count) has

proven more useful for tame white-tailed deer {Odocoileus

virginianus) (Bryant et al. 1979, Thill and Martin 1989),

and tame mule deer {Odocoileus hemionus) (Olson-Rutz and

Urness 1987) . Direct observation has also been used in

domestic livestock research (Erasure 1979, Sanders et al.

1980) .

Free et al. (1971), working in a semi-arid Colorado

environment, found that whether using bite count or

8

esophageal fistula, a similar estimation of cattle diets can

be obtained. When using these techniques, he suggested that

reliable estimates depended upon the observer more than other

parameters such as density and diversity of plants. Erasure

(1979) working at the Welder Wildlife Refuge (Texas Coastal

Bend) compared bite count versus fecal analysis, concluding

that these methods gave similar results for cattle diets.

Since no comparison of esophageal-fistula (EF) and bite-count

(BC) techniques had been carried out in diverse and rich

vegetation types such as those found in the Texas Coastal

Bend, my objective was to determine the botanical similarity

of cattle diets estimated from the esophageal and bite-count

techniques.

Materials and Methods

The study area was located at the Rob and Bessie Welder

Wildlife Refuge, San Patricio County, Texas. The 1.7-ha

pasture used for this experiment was characterized as a

mesquite-mixedgrass community, in which grasses such as

buffalograss {Buchloe dactyloides), longtom {Paspalum

lividum), and little bluestem {Schizachyrium scoparium) were

dominant. Prairie coneflower {Ratibida columnaris) and clay

violet {Ruellia nudiflora) were the dominant forbs. Wood-

sorrel {Oxalis dillenii) also occurred in patches.

Measurements of vegetation were not conducted since I was

10

interested only in comparing diet sampling techniques.

Botanical names and plant identification follow taxonomy by

Gould and Box (1965) and Jones (1982) (Appendix A.1-A.3).

A total of 90 samples of cattle diets was collected in

August, September, and November, 1988, and February, May, and

July, 1989. Diet samples were obtained from five randomly-

selected, esophageally-fistulated steers observed during

three to four consecutive days per month. To increase

appetite of the steers, they were penned without food or

water for at least 12 hours the night before sampling.

Observation was conducted in the early morning. Steers were

fitted with a screen-bottom collection bag and allowed to

roam free in the pasture while the observer recorded the

number of bites of each species. Steers were sequentially

observed feeding for 25 bites until a minimum of 100 bites

per steer were recorded. Selection of plant parts was not

recorded. Data were recorded on tape and transcribed to a

computer. All BC data collection was carried out by the same

observer.

Extrusa samples were allowed to drain in the collection

bag for at least two hours. A subsample of the diet was

preserved in ethyl alcohol and prepared for microhistological

analysis according to Scott and Dahl (1980). An aliquot of

each sample was mounted on five microscope slides. From each

slide, 20 fields were read to identify plant species based on

11

a reference collection of plant specimens previously

collected in the field. Analysis of the botanical

composition was conducted by two highly trained observers at

the Department of Range and Wildlife Management, Texas Tech

University.

Species were pooled into three forage classes: forbs,

grasses, and browse. Diet data were analyzed using the

General Linear Model of Statistical Analysis System (SAS

1985) through a completely randomized design with a split-

plot in time arrangement (Tables B.1-B.3). Replication was

represented by animals. Each estimated species/forage class

mean obtained by BC was compared to that obtained by

microhistological analysis of EF samples using Fisher's

Protected LSD at the 95% confidence level.

Results

Across sampling periods and all species, these two

techniques were different (P<0.05) in detecting forbs and

grasses, but were similar (P>0.05) in detecting browse in the

cattle diets (Tables B.1-B.3, Fig. 2.1). Each month, data

collected using the BC technique revealed a trend of higher

composition of grasses and lower composition of forbs than

the EF (Fig. 2.2). Regardless of the technique used, cattle

ate different (P<0.05) amounts of grass and forbs from month

12

o c: o & o u hi

0) > -H 4J (XJ

EH

H

EH

w o w

L J Bite Count HI Esophageal Fistula

FORBS GRASSES BROWSE

Figure 2.1: Cattle diets as determined by the bite-count and the esophageal-fistula methods for different forage classes. Means with the same letter within forage class are not significantly different (P>0.05).

13

Forbs

o 0)

<D U Ui

> - H 4-» <0 rH 0) AUG OCT NOV FEB MAY J U L

EH W M Q

:2:

EH

W

o w

D Bite Count Esophageal F i s t u l a

Grasses

AUG OCT NOV FEB MAY J U L

Figure 2.2: Monthly cattle diets by forage class as determined by the bite-count and the esophageal-fistula techniques.

14

to month (Tables B.1-B.3, Fig. 2.2). This may reflect the

the availability of forage and selectivity of cattle.

The number of plant species detected by either technique

varied with the sampling period (Table 2.1). Although I

detected more plant species using the EF technique, most of

them were detected only in trace amounts and probably were

not an important contribution to cattle diets (Table 2.2).

Overall, more forb and grass species were detected by the EF

method (37 and 28, respectively) than with the BC (23 and 19,

respectively) (Table 2.1) . A total of 41 plant species were

common in diets estimated from both techniques.

Overall, 13 species were detected in amounts greater

than 2% of the diet, 5 were forbs and 8 were grasses.

Considering only those species comprising more than 2% of the

diet, 93% of the diet was accounted for by the BC method,

while the EF method accounted for only 79%. Among the most

important forbs in the cattle diet, Oxalis dillenii was

detected similarly (P>0.05) by either technique (Table 2.2).

Buchloe dactyloides and Schizachyrium scoparium were among

the most important grasses used by cattle, however they were

detected differently (P<0.05) by the two techniques (Table

2.2). Of the grass species comprising more than 2% of the

diet, almost twice as much Buchloe dactyloides was detected

using the BC technique (47%) compared to the EF technique

15

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20

(28%) (Table 2.2) . Dichanthium annulatum was the only one

detected similarly (P>0.05) by the two techniques (Table 2.2).

Discussion

Mclnnis (1976) and Mclnnis et al. (1983) established

that the most accurate method to determine food habits of

ungulates is the esophageal fistula. In my study, diets

obtained by BC detected fewer plant species when compared to

EF. Also, forbs were estimated in lower proportions using

the BC method compared to the EF method. On the Welder

Wildlife Refuge where density and diversity of plant species

is high, I expected these results. Since the BC method was

conducted on foot and observations were conducted 1-4 m from

the animal, plant species should have been identified easily.

However, a potential problem when using direct observation to

obtain cattle diets relates to the way cattle consume

vegetation. Inaccurate observation of the plant species

being eaten by cattle can be related to the wide mouth and

the sweeping prehension movements of the tongue of these

animals. Several plant species can be taken in one bite for

which the observer will be able to see the most obvious

species only; e.g., the long blades of grasses or large,

broad leaves of forbs. For a narrow-mouth species such as

deer, direct observation may be not as biased as with broad-

mouth animals. Thus, vegetational complexity and cattle

21

grazing behavior may help explain why forbs were

underestimated using BC.

Reliable diet estimates also would be dependent upon the

observer experience in a complex plant community (Free et al.

1971) . In my study an experienced observer was used, one who

had been studying the flora for several months before the

experiment. Thus the vegetational complexity and the way

cattle consume vegetation could have been important factors

in the observed discrepancy between the number of plant

species detected when using the BC and the EF techniques.

It is noteworthy that when only plants contributing

greater than 2.0% of the diet were examined, the BC diets

contained a greater proportion of those species in the EF

diets. Thus the BC technique may be acceptable if analyses

are limited to only those plant species making up > 2.0% of

the diet.

Conclusions

This study indicates that using the BC and EF techniques

to determine cattle diets in the Texas Coastal Bend gave

different results for forage classes and plant species

ingested by cattle. Grasses, the main forage class used by

cattle, were detected differently by the two techniques

(P<0.05). The BC technique detected grasses in greater

dietary amounts than the EF technique. This was especially

22

true of the two most important dietary constituents Buchloe

dactyloides and Schizachyrium scoparium. These results are

related to the high density and diversity of the vegetation

complex at the Welder Wildlife Refuge and to the ingestion

mechanism of cattle.

Either technique has its advantages and disadvantages

depending upon the environment, the level of resolution

required, and the animal species being used. In the Texas

Coastal Bend the EF method should be used when information on

floral diversity or botanical composition of cattle diets is

needed. Research using the BC method for cattle diets should

only report data as forage classes. Even though BC

overestimates grasses and underestimates forbs, the method

provides a reasonable estimate of forage classes consumed by

cattle throughout the year. Further, if only species

comprising greater than 2% of the diet are included, the BC

technique will estimate a greater percentage of the diet than

the EF technique.

23

Literature Cited

Bryant, F.C, M.M. Kothmann, and L.B. Merrill. 1979. Diets of sheep. Angora sheep, Spanish goats and white-tailed deer under excellent range conditions. J. Range Manage. 32:412-417.

Erasure, J. R. 1979. The effects of three grazing management systems on cattle diets on the Welder Wildlife Refuge. M.S. Thesis. Texas Tech Univ. Lubbock, TX. 93 pp.

Free, J.C, P.L. Sims, and R.M. Hansen. 1971. Methods of estimating dry-weight composition in diets of steers. J. Anim. Sci. 32:1003-1008

Gould, F.W. and T.W. Box. 1965. Grasses of the Texas Coastal Bend. Texas A&M University, College Station, TX. 18 6 pp.

Holecheck, J.L., M. Vavra, and R.D. Pieper. 1982. Botanical composition determination of range herbivore diets: a review. J. Range Manage. 35:309-315.

Jones, F.B. 1982. Flora of the Texas Coastal Bend. Welder Wildlife Foundation. Mission Press, Corpus Christi, TX. 2 67 pp.

Kessler, W.B., W.F. Kasworm, and W.L. Bodie. 1981. Three methods compared for analysis of pronghorn diets. J. Wildl. Manage. 45:612-619.

Mclnnis, M.L. 1976. A comparison of four methods used in determining the diets of large herbivores. M.S. Thesis. Oregon State Univ Corvallis, OR. 127 pp.

Mclnnis, M.L., M. Vavra, and W.C Krueger. 1983. A comparison of four methods used in determine the diets of large herbivores. J. Range Manage. 36:302-306.

Olson-Rutz, K.M. and P.J. Urness. 1987. Comparability of behavior and diet selection of tractable and wild mule deer. Utah Dept. Nat. Res. Pub. No. 88-3. 40 pp.

Sanders, K.D., B.E. Dahl, and G.Scott. 1980. Bite-count vs fecal analysis for range animal diets. J. Range Manage. 33:146-149.

SAS. 1985. SAS User's Guide: Statistics, Version 5 Edition. SAS Institute Inc. Gary, N C

24

Scott, G. and B.E. Dahl. 1980. Key to selected plant species of Texas using plant fragments. Occasional Papers, The Museum, Texas Tech Univ. Lubbock, TX. 37 pp.

Short, H.L. 1962. The use of a rumen fistula in a white-tailed deer. J. Wildl. Manage. 26:341-342.

Thill, R.E. and A. Martin. 1989. Deer and cattle diets on heavily grazed pine-bluestem range. J. Wildl. Manage. 53:540-548.

Torrell, D.T. 1954. An esophageal fistula for animal nutrition studies. J. Anim. Sci. 13:878-882.

Veteto, C , C E . Davis, R. Hart, and R.M. Robinson. 1972. An esophageal cannula for white-tailed deer. J. Wildl Manage. 36:906-912.

CHAPTER III

FOOD HABITS AND DIETARY OVERLAP OF CATTLE

AND DEER UNDER DIFFERENT GRAZING SYSTEMS

AND STOCKING RATES

Introduct ion

Animal species that share a common resource may use

different strategies to exploit it. Environmental factors

such as droughts or wet periods and animal characteristics

such as mouth morphology, gut morphology and physiology, body

size, and behavior are proximate factors that shape such

strategies.

Livestock management can affect the strategy used by

wild ungulates to exploit resources. Factors such as

artificial barriers (fences), grazing systems, and stocking

rates could increase the pressure on wild species for a rapid

adaptation to the newly-created environment. This may be the

case for white-tailed deer (Ociocoiieus virginianus) when

interacting with cattle under grazing systems imposed by man.

Short-duration grazing (SD) has been a controversial

grazing strategy used by many ranchers since its introduction

to the USA (Savory and Parsons 1980, Heitschmidt et al. 1982,

Pitts 1983, Dickerson 1985, Bryant et al. 1989). Continuous

grazing (CG) has been the traditional grazing practice for

many years. A conflict arises when a rancher desires profits

25

26

from both wildlife and livestock without negatively affecting

the wild species or the rangeland.

Although studies have been conducted in many regions to

evaluate different grazing systems and stocking rates, little

is known about how SD and CG under different stocking rates

affect deer or cattle in the Texas Coastal Bend. The

objectives of this study were (a) to examine the initial

vegetation homogeneity and floral changes over time in the

plant community under study, (b) to determine the botanical

composition of cattle and deer diets under SD and CG, each

under heavy and moderate stocking rates, and (c) to determine

the magnitude of the dietary overlap between cattle and deer

under these conditions.

Study Site

The study was conducted at the Rob and Bessie Welder

Wildlife Refuge, San Patricio County, Texas. The 3,157-ha

refuge is located in the Coastal Bend region, a transitional

zone between the Gulf Prairies and Marshes and the South

Texas Plains (Thomas 1975). The climate can be described as

humid, subtropical with hot summers and cool winters. The

refuge has an average yearly rainfall of 89.2 cm, varying

among years from a low of 37.5 cm to a high of 148.7 cm.

Rainfall can occur any time of the year, but usually peaks in

late summer and fall. Permanent vegetation of the area is

not controlled by the average rainfall, but by the extremes.

27

Plant growth can occur every month of the year if moisture is

available (Box et al. 1970). At the study area average

annual rainfall from 1962 to 1988 was 95.3 cm. In 1987,

annual rainfall was 88.8 cm although most (41.7 cm) of it

fell during the second quarter. A drought hit the Coastal

Bend during 1988 when rainfall was only 60.3 cm, most (32.3

cm) of which came in the third quarter. During 1989 the

drought continued and the area received only 11.7 cm of

rainfall in the first six months.

Grazing treatments were established near the Lagarto

Tank. This site was chosen based on homogeneity of the

mesquite-mixedgrass plant community in that area of the

refuge. This community is found throughout the region on

poorly-drained Victoria clay soils. It is characterized by

moderate stands of honey mesquite {Prosopis glandulosa) ,

interspersed with mottes of brasil {Condalia hookeri), and

Texas persimmon {Dyospiros texana). Buffalograss {Buchloe

dactyloides), pink tridens {Tridens congestus) , and

bermudagrass {Cynodon dactylon) are the dominant grasses.

Among forbs Prairie coneflower {Ratibida columnaris), western

ragweed {Ambrosia psilostachya) , clay violet (i ueiiia

nudiflora), and patches of wood-sorrel {Oxalis dillenii) are

the dominants. Sumpweed {Iva annua) was a dominant forb

after heavy rains in June 1987. Botanical names and plant

identification follow taxonomy by Gould and Box (1965) and

Jones (1982) (Appendix A.1-A.3).

28

Methods

Grazing Treatments

Diet sampling was conducted with deer and cattle on two

grazing systems (SD and CG) and two stocking rates (heavy and

moderate) from October 1987 to July 1989. All treatments

were replicated (reps = 2). Moderate stocking rates were set

at 1 AU/4.9 ha/yr, a stocking rate commonly used in the

Coastal Bend; whereas, pastures receiving heavy stocking

rates were stocked at twice the moderate rates, 1 AU/ 2.4

ha/yr.

The treatments and replications were located in areas in

which similar grazing practices had been used since 1974.

The CG was part of the Mesquite Pasture, which had been

grazed continuously prior to this study for 12 yrs. The SD

was part of East Moody Pasture, a pasture grazed under a

1-herd, multi-pasture system similar to SD (Drawe and Cox

197 9). Short-duration and CG pastures were fenced in January

1987 and stocked with cattle in March 1987. The SD treatment

pastures and replications were subjected to a rigid rotation

of 28 days of rest (no cattle grazing) and 4 da of grazing.

Cattle that grazed the SD treatments were kept in a nearby

pasture when the SD pastures were being rested. The location

of the treatment pastures (Fig. 3.1) allowed the experimental

animals (deer and cattle) to remain in the vicinity for

access as well as for conditioning to seasonal changes of the

flora.

29

B

3^ Welder Widlife Refuge s (San Patricio County)

Fistulated cattle/ pastures /

D

Short Duration Heavy

4 ha

<

Short Duration

Moderate

4 ha

^

Short Duration Moderate

4 ha

«i

Short Duration Heavy

4 ha

^ Continuous / Grazing / Moderate

/ 8 ha

r n u

Continuous

Grazing Heavy 8 ha

Continuous Grazing

Heavy 8 ha

Continuous Grazing Moderate

8 ha

Figure 3.1: Study area (a) Texas location of study site and (b) design and distribution of treatment pastures and replications.

30 Deer Diets

Tame deer were used to obtain information on deer diets.

Although only does were used in this experiment, they should

provide unbiased deer diet information (La Gory et al. 1991).

Detailed explanation on raising and care of deer used in this

study are found elsewhere (Ortega et al. 1990, Ortega 1991).

During non-sampling periods, the routine was for deer to be

kept inside a pen (784 m^) at night, while during the day for

around nine to 10 hrs, they were allowed to roam and feed in

a holding pasture (0.5 ha) of vegetation similar to the

treatment pastures (Fig. 3.1). This allowed the deer to

become familiar with vegetation changes on the study area.

Deer were supplemented with 750 g/deer/day of 16% protein

pellet and 750 g/deer every other day of alfalfa hay. To

increase the appetite of deer in the morning during foraging

trials, alfalfa hay was not provided and the animals were

allowed to stay in the holding pasture for only 4-5 hours.

Foraging trials were conducted during early morning from

6:30 AM to 8:30 AM, lasting an average of 38 min (Range = 25-

85 min). Observations were conducted by the same observer of

four randomly selected deer (from a total of nine tame deer

available for sampling) in each replication 1-da/mo for

almost 2 yr. On the day of each trial, four deer were taken

to a pre-determined treatment pasture (replication) by having

the deer follow the observer. Deer were herded toward the

pastures by an assistant to prevent deer from feeding while

31

in transit. When in the pasture, deer were allowed to roam

freely. There was no influence by the observer on the

direction deer traveled, except when a deer tried to move to

another replication pasture. Deer were sequentially observed

feeding for 25 bites to complete a minimum of 100 bites/deer.

Bite-count data consisted of recording only plant species

that the deer consumed; no data were recorded on plant parts

consumed. Data were recorded on tape and transcribed to a

computer the same morning. A total of 68,239 bites was

recorded over the study period.

Cattle Diets

Diet samples were obtained in each replication 2-da/mo

from five randomly selected, esophageally fistulated steers

from a group of 12 animals. Fistulated steers were kept in

the vicinity of the treatment pastures year-round (Fig. 3.1).

To increase appetite of the steers, the night before sampling

they were penned without food or water for at least 12 hr.

Diet samples were collected in the early morning. Collection

of extrusa was made using screen-bottom canvas bags. Steers

were kept in the pasture treatments for at least 1 hr. After

sampling, animals were freed to graze in a 1.7-ha adjacent

pasture.

Extrusa samples were allowed to drain in the collection

bag for at least 2 hr. A subsample of the diet was preserved

in ethyl alcohol and prepared for microhistological analysis

according to Scott and Dahl (1980). A total of 708 samples

32

was collected. An aliquot of each sample was mounted on five

microscope slides. From each slide, 20 fields were read to

identify plant species based on a reference collection of the

plant specimens previously collected in the field. Analysis

of the botanical composition was conducted at the Department

of Range and Wildlife Management, Texas Tech University.

According to previous studies (Kie et al. 1980, Sanders et

al. 1980), there was no need to correct for over- or

underestimation of the microhistological readings unless

plants occurring in trace amounts occurred disproportionately

high in the diet. The few species that could have been over-

or underestimated, such as Sida filicaulis, had a very low

availability (< 2.0% frequency) and never comprised more than

2.0% of the diet of either animal species.

Vegetation Measurements

To document herbage biomass changes in the different

treatments, 10-0.25 m^ randomly-selected quadrats in every SD

and CG treatment replication were clipped to ground level the

day before grazing the SD treatment. These samples were

frozen and later separated by hand into the following

categories: desirable and undesirable forbs, desirable and

undesirable grasses, and desirable and undesirable grass-like

plants. The samples were oven dried and weighed after

separation into categories. Soltero-Gardea (1991) presented

a detailed analysis of these data.

33

To document changes in plant species availability and

floral diversity, 50-0.25 m^ randomly-selected quadrats/

treatment replication, were read for presence/absence

(species frequency). These data were collected each month in

all treatment replications 2-da before grazing the SD

treatment. To minimize error, data collection was done by

the same observer throughout the experiment. Data were

collected using a tape recorder and transcribed to a computer

in the lab after sampling.

The point-centered quarter method (Dix 1961) was used to

estimate availability of the woody vegetation. Sampling was

conducted from 8 to 14 August 1988. A total of 10 randomly-

selected line transects was sampled using five points in each

line, totaling 50 points per treatment replication. Data

were collected by a two-person team, a sampler and a

recorder. Relative frequency of the woody species was

determined from these data.

Data Analysis

Data were analyzed seasonally because effect of

treatment on ungulate diets could be more easily interpreted

than on a monthly basis. Seasons were established according

to growing season of the vegetation and climatic patterns.

They are as follows: Fall 1: Oct. and Nov. 1987; Winter 1:

Dec. 1987, Jan. and Feb. 1988; Spring 1: Mar. and Apr. 1988;

Summer 1: May, Jun., Jul., Aug., and Sep. 1988; Fall 2:

Oct. and Nov. 1988; Winter 2: Dec 1988, Jan. and Feb. 1989;

34

Spring 2: Apr. and May 1989; and Summer 2: Jun. and Jul.

1989.

In addition to botanical composition of treatment

pastures based on frequency of occurrence. Shannon's

diversity index (Magurran 1988) was calculated for the

different pastures to determine the homogeneity of the area.

These diversity indices were calculated for April 1986, 1988,

and 1989.

Cattle and deer diets were analyzed using canonical

discriminant analysis, a multivariate statistical technique

that allows study of differences between two or more groups

simultaneously (Klecka 1980, Lindeman et al. 1980). This

technique also has been used by Hanley and Hanley (1982) to

study resource partitioning among ungulates. Discriminant

analysis permits the separation of deer and cattle diets

under any of the treatments if the animals were eating

different plant species. In contrast, if deer or cattle

under any of the treatments were eating similar forages, they

would not be separated (Green 1971). This similarity would

be interpreted to mean that some overlap is occurring among

these animal species.

Discriminant analysis was applied to the diet data

pooled across all seasons and within seasons. In both

instances, plant species comprising less than 5% of the diet

in any one of the 8 groups (4 treatments x 2 animal species)

were not included. The most valuable plant species to

discriminate between the diets of animal species or the diets

as affected by the treatments were revealed by the

discriminant function coefficients (Hanley and Hanley 1982).

To test for statistical significance among groups, the F

ratio for the Mahalanobis distance between each pair of

groups was calculated (Hanley and Hanley 1982, Lindeman et

al. 1980; Appendix C.l). A separate univariate analysis for

deer and cattle diets using forage classes was analyzed using

the General Linear Model of Statistical Analysis Systems (SAS

1985) through a completely-randomized design with a split-

plot. The Morosita-Horn index (Magurran 1988; Appendix C.2)

was used to determine diet overlap between cattle and deer

(Schwartz and Ellis 1981). This index is recommended by

Wolda (1981) to avoid the complex handling of data in

relation to the effects of sample size and diversity.

Results

Study Area Homogeneity and Floral Changes

The study area was selected for visual homogeneity of

the plant community. A sampling of the herbage layer

conducted in April 1986 showed an average diversity index for

all the treatment pastures of H = 2.41. There was no

difference (P>0.05) among treatment pastures, with diversity

indices ranging from H = 1.95 to H = 2.63 (Table 3.1).

However, there was an increase in diversity in all the

pastures by April 1988 (H = 3.08) and a decrease in diversity

36 Table 3.1: Floral diversity index for the

different grazing treatments during April 1986, 1988, and 1989 at the Welder Wildlife Refuge. (S = short-duration grazing, C = continuous grazing, H = heavy stocking rate, M = moderate stocking rate, rl = replication 1, r2 = replication 2)

Pastures

SH rl

r2

SM rl

r2

CH rl

r2

CM rl

r2

1986

2.42

1.95

2.32

2.58

2.56

2.63

-

-

Year

1988

3.17

2.97

3.13

3.03

3.05

3.12

3.02

3.12

1989

2.53

2.58

2.74

2.81

2.49

2.54

2.68

2.53

37

in April 1989 (H = 2.61). Diversity of treatment pastures

was similar (P>0.05) in April 1986 and April 1989, but it was

different (P<0.05) between these two dates and April 1988.

There was no difference (P>0.05) in diversity among pasture

treatments or replication within years (Table 3.1).

Availability of most species was affected by season

(P<0.05), with the exception of Malvastrum aurantiacum,

Euphorbia prostrata, and Eryngium hookeri (P>0.05) (Tables

3.2-3.5) . Some species, i.e.. Ambrosia psilostachya, were

affected by the grazing system, an unexplainable interaction

of grazing system/stocking rate/season, i.e., Vicia

leavenworthii and Sporobolus asper, an unexplainable

interaction of grazing system/stocking rate, i.e., Paspalum

langeif or an unexplainable interaction of grazing

system/season, i.e., Marsilea macropoda, Oenothera speciosa,

and Hordeum pusiiiu/n(P<0.05) (Tables 3.2-3.5) .

From the herbage layer, the most frequently used plant

species by cattle and deer were analyzed to illustrate

homogeneity of the treatments (Table 3.6). Stipa leucotricha

was the only grass affected by the grazing system

(P<0.05)(Tables 3.6 and C.3). It occurred more frequently

under CG than SD. Buchloe dactyloides increased continually

throughout (P<0.05) (Tables 3.2-3.5, Table C 4 , Fig. 3.2).

Tridens congestus peaked in availability in the Fall 1,

Summer 1, and Summer 2 (P<0.05) (Table C 5 , Fig. 3.2) and had

a higher availability in the moderate than in the heavy

38 Table 3.2 Fall availability (percent frequency) of plant

species in the treatment pastures at the Welder Wildlife Refuge. (Species with a relative frequency > 2%; S = short duration, C = continuous grazing; H = heavy, M = moderate)

FALL 1 FALL 2

SM CM SH CH SM CM SH CH

FORBS

Ambrosia psilostachya 14.7 11.1 15.5 13.1 8.0 3.8 8a7 3.7

Commelina erecta 3.3 3.4 1.3 laO

Desmanthus vlrgatus 1.9 2.0 1.2 2.6 2.0 2.7 1.8 2.3

Iva annua 19.2 18.1 17.8 14.0 1.0 0.4 1.0 0.3

Lesquerella lindheimeri 0.7 1.0 2.7 3.1

Lythrum californicum 0.4 0.2 0.2 3.1 2.9 4.3 2.9

Machaeranthera tenuis 1.3 1.9 2.0 2.7 1.2 1.5 0.4 1.3

Malvastrum aurantiacum 2.4 2.0 2.9 2.3 1.9 2.4 2.6 1.8

Marsilea macropoda 1.5 2.2 1.3 0.9 2. .2. 3.5 3.3 3a6

Oenothera speciosa 0.5 0.1 0.6 0.3 1.3 1.1 2.0 1.4

Oxalis dillenii 0.3 0.2 0.1 0.4 4.2 4.4 3.8 3.9

Phyla incisa 2.2 5.3 4.0 5.1 4.4 7.6 6.2 5.7

Phyla nodiflora 1.0 1.5 0.7 3.6 2.6 4.3 1.8 3.7

Ratibida columnaris 1.8 5.3 1.9 5.0 2.5 5.2 3.8 3.2

Ruellia nudiflora 6.5 9.9 6.2 9.7 6.4 9.0 7.0 11.6

Tragi a brevispica 1.0 1.2 2.4 1.5

Table 3.2: Continued. 39

FALL 1 FALL 2


GRASSES AND SEDGES

Buchloe dactyloides 6.3 8.9 7.9 10.5 14.5 17.1 15.9 17.3

Cyperus acuminatus 7.8 7.5 5.8 5.9 4.9 6.8 4.9 6.5

Dichanthium aristatum 2.4 0.7

Paspalum lividum 2.2 0.9 2.3 2.2 1.8 1.5 1.7 2.1

Schizachyrium scoparium 4.2 8.2 3.1 4.4

Setaria genlculata 2.6 1.9 2.9 2.2

Sporobolus asper 8.2 5.3 5.2 3.8

Stipa leucotricha 0.8 0.8 0.4 2.6

Tridens congestus 12.6 10.4 10.1 9.6 3.7 2.3 2.2 2.6

40 Table 3.3: Winter availability (percent frequency) of plant


WINTER 1 WINTER 2


FORBS

Ambrosia psilostachya 11.0 8.0 11.7 9.8 8.7 3.8 7.8 3.1

Argythamnia humilus 1.0 1.0 0.4 1.1 2.2 2.1 2.1 3.4

Euphorbia prostrata 2.2 - 2.2 - 0.5 - 0.3

Euphorbia spathulata - 2.8 - 2.9 - 0.2

Geranium carolinianum 11.1 9.7 10.1 9.5 3.7 1.9 2.5 1.3

Lesquerella lindheimeri - - - - 7.1 8.2 12.3 12.0

Lythrum californicum 5.5 4.6 7.8 4.8 3.8 5.2 5.4 4.9


Marsilea macropoda 1.6 2.1 1.1 1.2 1.3 1.9 0.6 0.8

Nothoscordum bivalve 2.5 1.7 3.0 1.7 6.1 4.9 5.5 3.9


Oxalis dillenii 1.4 2.3 1.5 3.1 6.7 6.6 5.5 5.4

Phyla incisa 1.1 2.6 0.7 1.4 2.5 5.3 4.0 3.5

Phyla nodiflora 0.3 1.9 0.4 1.5 2.0 2.1 1.0 4.2

Phyrrhopappus multicaulis 5.7 7.7 5.9 8.3 - 0.1 - 0.4



Vicia leavenworthii 3.2 2.2 1.8 3.0 0.4 0.5 0.2 0.3

Table 3.3: Continued

WINTER 1 WINTER 2


GRASSES AND SEDGES




Schizachyrium scoparium 3.6 - 5.4 - 3.7 - 5.4

Stipa leucotricha - - - - 4.6 7.6 4.0 9.6


42 Table 3.4 Spring availability (percent frequency) of plant


SPRING 1 SPRING 2


FORBS

Ambrosia psilostachya 8.8 6.0 9.6 7.6 7a9 5a6 5.8 2.7


Chaerophylum tainturieri 2.8 3.6 4.7 4.3

Desmanthus vlrgatus 1.1 0.3 0.3 0.4 3.6 4.6 4aO 4a4

Eryngium hookeri 2.3 2.4 1.4 3.0

Euphorbia prostrata 4.7 5.7 0.6

Euphorbia spathulata 5.1 5.0 0.3


Iva annua 1.6 1.0 2.1 1.9 1.1 0.5 0.6

Lesquerella lindheimeri 1.9 3.1 1.8 4.6 3.0 4.4 5.7 5.1




Oenothera speciosa 6.9 7.8 5.3 6.0 0.7 0.3 1.1

Oxalis dillenii 2.8 3.1 2.8 2.9 1.9 2.8 3.0 1.8

Phyla incisa 0.8 1.2 1.1 1.4 2.1 5.9 6.6 7.6

Phyla nodiflora 0.1 1.7 0.4 1.0 1.4 2.6 2.5 2.2

Phyrrhopappus multicaulis 5.9 4.2 5.7 4.5 0.1


Table 3.4: Continued. 43

SPRING 1 SPRING 2



Senecio imparipinnatus 4 . 8 4 . 5 4 . 2 3 . 4

Tragi a brevispica 0.9 0.6 1.4 1.1 1.3 2.2

Vicia leavenworthii 3.9 2.7 2.4 2.7

GRASSES AND SEDGES



Hordeum pusillum 4.4 6.7 4.1 6.3 3.2 3.1 1.9 2.9

Paspalum langei 3.2 2.2 1.1 0.7


Schizachyrium scoparium 2.6 3.5 1.2 2.4

Stipa leucotricha 0.6 1.1 0.3 0.4 16.7 16.4 13.8 17.7


44 Table 3.5 Summer availability (percent frequency) of plant


SUMMER 1 SUMMER 2


FORBS



Commelina erecta 2.8 2.3 1.3 3.5

Desmanthus vlrgatus 4.2 3.1 3.0 4.3 5.6 4.1 4.9 4.2

Iva annua 2.9 1.1 2.4 1.4 0.3 0.3




Mimosa strigillosa 0.9 1.0 3.5 1.6

Oenothera speciosa 2.3 1.4 1.9 1.6

Oxalis dillenii 6.2 6.2 7.3 5.4 2.2 1.2 3.7 0.5

Phyla incisa 2.3 5.0 3.4 3.9 2.9 10.8 7.7 6.7

Phyla nodiflora 2.2 3.7 1.5 4.1 3.8 4.9 3.5 7.6

Ratibida columnaris 4.2 5.5 5.0 5.1 0.5 0.4


Tragi a brevispica 2.1 2 . 2 2 . 0 2 . 1

45 Table 3.5: Continued.

SUMMER 1 SUMMER 2


GRASSES AND SEDGES




Schizachyrium scoparium 3.0 - 4.3 - 3.8 - 6.8 -


Table 3.6: Availability (percent frequency) of the five species most frequently used by cattle and deer under different grazing treatments across all seasons and years 1987 - 1989 at the Welder Wildlife Refuge. (Grazing systems: SD = short-duration, CG = continuous; Stocking rates: H = heavy, M = moderate; Means with the same superscript between rows within grazing systems and stocking rates are not significantly different (P>0.05)).

46

Primary Forage Species

To Cattle:

Treatments

Grazing

Systems

Stocking

Rates SD CG H M

Buchloe dactyloides 1 2 . 9 ^ 1 5 . 9 a 1 5 . 8 ^ 13.Oa

Tridens congestus 6.6< 5.5' 4.9b 7.2^

Stipa leucotricha 2.3b 3.3a 2.7a 2.9a

Lesquerella lindheimeri 2.3< 2.6^ 3.0a 1.9a

Ratibida columnaris 5.0' 5.9< 5.3' 5.5a

To Deer

Oxalis dillenii 3.9< 3.7" 3.7a 3.8^

Commelina erecta 0.6' 1.4a 0.9a l.ia

Phyrrhopappus multicaulis 1.5' 1.6' 1.6' 1.5a

Geranium carolinianum 2.7a 2.3a 2.3a 2.73

Ratibida columnaris 5.0' 5.9a 5.3' 5.5a

> 1 o G Q) P

cr (D

i p

-p c Q) U

<u 0^

EH

PQ

t-: |

M

F - l W-1 S P - 1 S S - 1 F - 2 W-2 SP-2 SS-2

50

40-1 Tridens congestus

F-l W-1 SP-1 SS-1 F-2 W-2 SP-2 SS-2

F-l W-1 SP-1 SS-1 F-2 W-2 SP-2 SS-2

Figure 3.2: Seasonal changes in the availability (percent frequency) of grasses most heavily used by deer and cattle. Grazing systems: C = continuous, S = short-duration; Stocking rates: H = heavy, M = moderate. Across treatments different letters indicate difference of availability between seasons (P<0.05). Difference of availability within season under grazing system (GS) or stocking rate (SR) (P<0.05).

48

treatments during Fall 1, Winter 1, and Spring 2 (P<0.05)

(Tables 3.2, 3.3, 3.4). Stipa leucothricha peaked in

availability in Spring 2 (Tables 3.4, C.3, Fig. 3.2) and was

available in greater proportions in the CG than SD treatments

during Winter 2 (P<0.05)(Fig. 3.2).

Among the forbs, Lesquerella lindheimeri had a small

availability peak in Spring 1 and a larger peak in Winter 2

(P<0.05) (Tables 3.2-3.5, Table C 6 , Fig. 3.3), with a higher

availability in the CG than in the SD treatments

(P<0.05)(Fig. 3.3). Ratibida columnaris showed a steady

decline throughout the study in all treatments starting in

Winter 1 (P<0.05) (Tables 3.3-3.5, Table C 7 , Fig. 3.3).

Oxalis dillenii had a peak in Summer 1, declining towards the

end of the sampling (P>0.05) (Tables 3.2-3.5, Table C 8 , Fig.

3.3), with a higher availability in the heavy than in the

moderate treatments in Spring 2 (P<0.05) (Fig. 3.3) .

Commelina erecta peaked in Fall 1, Spring 1, and Summer 2

(P<0.05) (Table 3.3-3.5, Table C.9, Fig. 3.4). Phyrrhopappus

multicaulis peaked in Winter 1, decreasing in Spring 1 and

was practically unavailable the rest of the sampling period

(P<0.05) (Table 3.3-3.5, Table CIO, Fig. 3.4). Finally,

Geranium carolinianum peaked in Winter 1, decreasing in

Spring 1, with a second peak in Winter 2 (P<0.05) (Table 3.2-

3.5, Table C.ll, Fig. 3.4).

Analysis of the browse layer shows that several species

were similarly available throughout the area, regardless of

>1 o G Q) P tr (D

ip

-P G (U U

0) di

>H E-t

M

F-l W-1 SP-1 SS-1 F-2 W-2 SP-2 SS-2

F-l W-1 SP-1 SS-1 F-2 W-2 SP-2 SS-2

20

15

Oxalis dillenii

F-l W-1 SP-1 SS-1 F-2 W-2 SP-2 SS-2

Figure 3.3: Seasonal changes in the availability (percent frequency) of forbs most heavily used by deer and cattle. Grazing systems: C = continuous, S = short-duration; Stocking rates: H = heavy, M = moderate. Across treatments, different letters indicate difference of availability between seasons (P<0.05). Within season, difference in availability are indicated by GS (grazing system) or SR (stocking rate) (P<0.05)

> 1 u G Q) P tr (U

cpi

-P C 0) O 5-1 CU

EH

CQ

M

i

50

F - l W-1 S P - 1 S S - 1 F - 2 W-2 S P - 2 S S - 2

20

15-1

Phyrrhopappus multicaulis

W-1 SP-1 SS-1 SP-2 SS-2

F-l W-1 SP-1 SS-1 F-2 W-2 SP-2 SS-2

Figure 3.4: Seasonal changes in the availability (percent frequency) of forbs most heavily used by deer and cattle. Grazing systems: C = continuous, S = short-duration; Stocking rates: H = heavy, M = moderate. Across treatments, different letters indicate difference of availability between seasons (P<0.05). Within season, difference in availability are indicated by GS (grazing system) or SR (stocking rate) (P<0.05)

51

grazing treatment. Prosopis glandulosa was the most abundant

brush species on the study area (Table 3.7).

Cattle and Deer \^]f^i-^

Through canonical discriminant analysis, the diets of

deer and cattle were found to be distinct from each other in

every treatment across the entire sampling period (Fig. 3.5).

The differences were significant (P<0.001)(Table 3.8). As

indicated by the distances between the centroids, in most of

the seasons, diets were similar in composition when comparing

cattle versus cattle or deer versus deer under the different

treatments (Table 3.9).

Overall, disregarding treatments, cattle ate mostly

grasses (60%) and forbs (39%), while deer used forbs

(72%)(Table 3.10). The first function of the discriminant

analysis shows that the forbs 0. dillenii, Ruellia nodiflora,

and Desmanthus vlrgatus, mostly consumed by deer, and the

grasses T. congestus, B. dactyloides, and S. leucotricha,

mostly eaten by cattle, were the primary plant species

separating deer diets from cattle diets (Fig. 3.5). The

second discriminant function explains the effects of grazing

systems on diets. Consumption by deer of the forbs Commelina

elegans, C. erecta, R. columnaris, and Ambrosia psilostachya,

and consumption of cattle of the grasses Schizachyrium

scoparium, and Paspalum lividum were the key plants that

separated the diets under CG from SD grazing (Fig. 3.5).

Table 3.7: Browse availability (percent frequency) in the treatment pastures at the Welder Wildlife Refuge. (S = short duration, C = continuous grazing; H = heavy, M = moderate)

52

TREATMENTS

SPECIES S M C M S H C H

Acacia farnesiana 17.9 10.1 19.3 10.5

Acacia tortuosa 6.1 4.2 9.1 2.5

Berberis trifoliolata 1.7 1.2 3.1

Celtis laevigata

Celtis pallida

0.5

1.1

3.6

0.6

1.9 0.6

1.8

Condalia hookeri 0.5 3.0 1.3 2.5

Diospyros texana 0.5 3.0 0.6 1.2

Eysenhardtia texana 3.3 0.6 1.2 0.6

Forestiera angustifolia 1.1 1.2 0.6

Lycium berlandieri 0.6 0.6

Prosopis glandulosa 61.8 65.7 65.4 67.0

Prosopis reptans 1.7 4.7 5.7

Zanthoxylum fagara 2.2 2.4 0.6 3.1

Ziziphus obtusifolia 1.1 0.6

53

2 -

M M

CO M

X 0

- 2 -

- 4

-

^Cattle/CH ^ •Cattle/CM

•Cattle/SM • Cattle/SH

1

Deer/CH^ Deer/CM^

Deer/SH^.^ Deer/SM

1 - 4 - 2 0

0. dillenii, R. nudiflora, D. virgatus ^ >

< > T. congestus, B. dactyloides, S. leucotricha

AXIS I

A

TJ

o CJ

a:

TJ •u o QJ U Q)

OJ

0)

•0 • H

o <a •u 0)

o

CO

5 3

• H

Q<

e 3

•H U m a o o

CO

V

Figure 3.5: Plot of canonical discriminant centroids of deer and cattle diets for each grazing treatment pooled across seasons. Direction of arrows bordering the figure indicates most valuable plant species for discrimating between the diet composition of the various groups.

54 Table 3.8: Levels of significance F-values for the

discriminant analysis used to separate cattle and deer diets throughout the study period at the Welder Wildlife Refuge. [Asterisks indicate significant difference between the groups within seasons:* = P<0.01; ** = P<0.005; *** = P<0.001, ns= not significant (P>0.01); C = continuous grazing, S = short-duration grazing, H = heavy stocking rate, M = moderate stocking rate]

C o n t r a s t s F a l l W i n t e r S p r i n g Summer F a l l W i n t e r S p r i n g Summer O v e r a l l 1 1 1 1 2 2 -1 2

D e e r - C a t t l e

CH * CH

CH * CM

CH * SH

CH * SM

CM * CH

CM * CM

CM * SH

CM * SM

SH * CH

SH * CH

SH * CM

SH * SM

SM * CH

SM * CH

SM * CM

SM * SM

* * * * *

* * * * *

* * * * * * * * * * * * * * * * * * * * * * * * * * *

* * * * * • * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * * * * * * *

* • * * * * * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * • * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * * * * * * *

* * * * * * * • * * * * * * * * * * * * * * * * * * *

* * * * * • * * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * *

* * * * * *

* * * * * *

* * • * * *

* * * * * *

55 Table 3.9: Levels of significance of F-values for the

discriminant analysis used to contrast cattle/cattle and deer/deer diets under different treatments throughout the study period at the Welder Wildlife Refuge. [Asterisks indicate significant difference between the groups within seasons: * = P<0.01; ** = P<0.005; *** = P<0.001, ns = not significant (P>0.01); C = continuous grazing, S = short-duration grazing, H = heavy stocking rate, M = moderate stocking rate]

C o n t r a s t s F a l l W i n t e r S p r i n g Summer F a l l W i n t e r S p r i n g Summer 1 1 1 1 2 2 2 2

C a t t l e - C a t t l e

CM*CH n s n s n s ** n s *** n s n s

SH*CH n s n s ns *** n s ns n s ns

SH*CM n s n s ns *** n s ** ** ns

SM*CH n s n s n s *** ns ** * **

SM*CM n s n s n s *** ** ns n s n s

SM*SH n s n s n s *** n s ** ** *

D e e r - D e e r

CM*CH n s n s n s n s ns ** ns *

SH*CH n s ** n s *** n s *** ns ***

SM*CH n s ** ns *** ns *** ns ***

SH*CM n s ** n s *** ** *** ns **

SM*CM ** n s n s *** ** *** ns **

SM*SH n s n s ns n s n s ** n s n s

56

Table 3.10: Forage classes (dietary percent) used by deer and cattle throughout the study, 1987-1989 at the Welder Wildlife Refuge, (s.d. = standard deviation).

Species

Cattle

s.d.

Deer

s.d.

Forbs

39.1

15.2

72.2

28.5

Grasses

59.9

15.4

14.2

15.1

Browse

1.0

3.1

13.6

19.0

57

For cattle and deer, according to univariate analysis,

neither the grazing system nor stocking rate affected

(P>0.05) their use of forbs, grasses, or browse (Tables 3.11

and C.12-C17). However, using deer-deer statistical

comparison with multivariate statistics (Table 3.9), provides

a comprehensive index of deer sensitivity to local conditions

(i.e., grazing treatments). Comparing seasons, deer were

most sensitive to summer conditions both years because diets

were different (P<0.01) when deer fed in the various

treatment pastures. After summer, deer were most sensitive

in winter during the drought, followed by fall. Deer

sensitivity to treatment pastures was the least during the

spring both years. Across seasons, deer were least sensitive

to conditions created by stocking rates within grazing

systems. For example, within CG deer were sensitive to

stocking rate (diets were different between CH and CM) in

only 2 of 8 seasons (Table 3.9). Similarly, within SD, deer

were sensitive to stocking rate only in Winter 2. Deer were

most sensitive to vegetal conditions between CM and SM and CM

and SH. Diets were different in 5 of 8 seasons.

Diet composition by season varied between deer and

cattle under the different treatments. However, diets of

deer and cattle were different throughout the 22-mo sampling

period as indicated by the first discriminant function

(Figs. 3.6-3.7).

Table 3.11: Forage classes (dietary percent) used by cattle and deer as influenced by grazing systems and stocking rates at the Welder Wildlife Refuge. Within animals species, means for forage classes between grazing systems or stocking rates were not different (P>0.05) (s.d. = standard deviation).

58

Cattle

Grazina System

Short-duration

s.d.

Continuous

s.d.

Stockina Rate

Heavy

s.d.

Moderate

s.d.

Deer

Grazina System

Short-duration

s.d.

Continuous

s.d.

Stockina Rate

Heavy

s .d.

Moderate

s .d.

Forbs

36.2

14.6

41.8

15.2

42.9

14.6

35.2

14.7

68.7

23.8

74.9

25.9

71.4

24.3

71.8

25.7

Grasses

63.2

14.7

56.7

15.4

55.8

14.6

64.1

15.0

18.7

17.2

9.8

10.5

14.3

14.7

14.2

15.4

Browse

0.6

1.2

1.5

4.2

1.3

4.0

0.7

1.9

12.6

16.7

14.6

21.5

13.7

18.9

13.8

19.6

H M

W H

B.

R. nudiflora, C. erecta, r . congestus, B. wildenowii, P. glandulosa L . lindheimeri

. < ]

dactyloides, T. congestus.

59

R. columnaris, I. ann ua

3

i>

Q<

A 8 i>

P. multicaulis, R. columnaris

[>

2

m

0)

6

V A

«0

<0

o o

CC,

6

4

2

0

- 2

- 4

- 6

- 8

6

4

2

0

- 2

- 4

- 6

- 8

D e e r

^CM

• c H

• •sM SH

FAL

C a t t l e

CH • • C M

^SH *SM

SPRI

C a t t l e

CM CM

CH^^'SH

L 1

D e e r

• CM • CH

^"•SM

NG 1

C a t t l e

CM CH • • ^ ^ S H

D e e r •CH • CM

• SM • SH

WINTER 1

C a t t l e

C M ^ ^ ^ «

^ " • • S H

D e e r

CH CM^

• SM *SH

SUMMER 1

3 H

CX o o to

CO

A

oc

V

6 3

•H

m § o to

CO

V

- 8 - 6 - 4 - 2 0 6 8 - 6 - 4 - 2 0 8

B. willdenowii, L. lindheimeri, T. congestus, B. dactyloides, T. congestus s . leucotricha, M. aurantiacum

<\ ^

P. multicaulis, L. californicum

> O. dillenii

->

AXIS I

Figure 3.6: Plot first each borde plant diet CM = heavy SH =

of canonical discriminant centroids for year of deer and cattle diets for grazing treatment. Direction of arrows ring the figure indicates most valuable species for discrimating between the composition of the various groups. continuous moderate, CH = continuous , SM = short-duration moderate, short-duration heavy.

<XJ

Cn

1X1

o +J CO

o ••s

CO

H H

W H

V A

CD

e

S. scoparium, S. leucotricha, T. congestus, D. annulatum

< • <J-

60

O. dillenii

A 8 6

S. leucotricha, T. congestus, R. nudiflora, C. erecta S. dactyloides, P. incisa

1> >

4

2

0

-2

-4

-6

-8

6

4

2

0

-2

-4

-6

-8

Cattle

CM^ CH^

S^^""

FAL]

Cattle SH^

CH SM^ ^ CM^

Deer • CM

ACH

• SM *SH

L 2

Deer

SH#CH CM^SM

SPRING : /

Deer

CH^

CM^

^•SH SM^

Cattle

• CH

^M

WINTER 2

Cattle

CM^^CH SM* *SH

Deer •CH

• CM

SM SH

SUMMER 2

CO

V

-8 -6 -4 -2 0 8 -6 -4 -2 0 8

T. congestus, S. leucotricha, B. dactyloides, T. congestus, B. dactyloides, D. annulatum 3- leucotricha

<-

O. dillenii, R. nudiflora

^ virgatus

-[>

Figure 3.7:

AXIS I

Plot of canonical discriminant centroids for second year of deer and cattle diets for each grazing treatment. Direction of arrows bordering the figure indicates most valuable plant species for discrimating between the diet composition of the various groups. CM = continuous moderate, CH = continuous heavy, SM = short-duration moderate, SH = short-duration heavy.

61

During Fall 1, cattle diets were similar across all

treatments (Table 3.9, Fig. 3.6). Deer diets were similar in

all treatments except between grazing systems under moderate

stocking (Table 3.9, Fig. 3.6). As reported by Soltero-

Gardea (1991), the dietary crude protein in deer under SD was

at the maintenance level, while in the CG it was higher than

maintenance level. During this season deer in the SD used

more grasses (40%) such as P. lividum and only 30% forbs,

while in CG deer used mainly forbs (50%), browse {Prosopis

gladulosa beans), and very little grass (Figs. 3.8-3.10).

In Winter 1, cattle diet composition under the different

treatments was still similar, while deer diets were different

because of the effect of the grazing systems, but not

stocking rate (Table 3.9, Fig. 3.6). Deer increased

consumption of forbs which resulted in dietary crude protein

higher than the maintenance level in all treatments (Soltero-

Gardea 1991). Species such as R. columnaris and P.

multicaulis were important to deer diets at this time.

Although there was no difference from Fall 1 in the

consumption of forbs by cattle (Fig. 3.8), their level of

crude protein dropped under the maintenance level in the CG

treatments and under heavy stocking (Soltero-Gardea 1991).

During Spring 1, cattle diet composition was similar

across all treatments, as were deer diets (Table 3.9, Fig.

3.6) . Deer use of forbs increased from winter to spring

(Fig. 3.8), but the crude protein level dropped

0)

-P c (U o u

100

62 Cattle - CG

Cattle - SD

Deer - CG

Deer - SD

Grazing System

0 1 1 \ 1 1 1 F-l W-1 SP-1 SS-1 F-2 W-2 SP-2 SS-2

100

•*- Cattle - Heavy

-B— Cattle - Moderate

Deer - Heavy

Deer - Moderate

Figure

W-1 SP-1 SS-1 F-2 W-2 SP-2 SS-2

Use of forbs by deer and cattle under continuous (CG) and short-duration grazing (SD); and heavy and moderate stocking rates during 1987-1989 at the Welder Wildlife Refuge. Different letters indicate difference within season (P<0.05). No letters indicate no difference within season.

63

Q)

D

100

F-l

••- Cattle - CG

-B- Cattle - SD

Deer - CG

Deer - SD

Grazing System

W-1 SP-1 SS-1 F-2 W-2 SP-2 SS-2

-p c <D U U <D 100

80-

Cattle - Heavy

-Q- Cattle - Moderate

Deer - Heavy

Deer - Moderate

F-l

Figure 3.9

Stocking Rate

W-1 SP-1 SS-1 F-2 W-2 SP-2 SS-2

Use of grasses by deer and cattle under continuous (CG) and short-duration grazing (SD); and heavy and moderate stocking rate during 1987-1989 at the Welder Wildlife Refuge. Different letters indicate difference within season (P<0.05). No letters indicate no difference within season

Q) CO

-P G (U O U <D CU

Cattle - CG

-B- Cattle - SD

Deer - CG

Deer - SD 100

80

64

Grazing System

60-

F-1 W-1 SP-1 SS-1 F-2 W-2 SP-2 SS-2

Cattle - Heavy Deer - Heavy

-O— Cattle - Moderate —O— Deer - Moderate 100

Stocking Rate

80-

60-

SP-2 SS-2

Use of browse by deer and cattle under continuous (CG) and short duration grazing (SD); and (b) heavy and moderate stocking rate during 1987-1989 at the Welder Wildlife Refuge. Different letters indicate difference within season (P<0.05). No letters indicate no difference within season

65

(Soltero-Gardea 1991). Cattle increased forbs use, which

explains the observed increased level of dietary crude

protein as reported by Soltero-Gardea (1991). The forbs, R.

columnaris, P. multicaulis, Lythrum californicum, Lesquerella

linheimeri, and the grasses Bromus willdenowii, and T.

congestus were important plant species consumed by cattle and

deer during that period (Table C.20, Fig. 3.6).

In Summer 1, both cattle and deer diets were affected by

the grazing systems, while cattle diets also were affected by

the stocking rates (Table 3.9, Fig. 3.6). The effect of the

treatments on the diets of either animal species made their

diets different when making intra-species comparison. By

this time of the year, deer were concentrating heavily on

patches of O. dillenii, especially under moderate stocking

rates. Deer diets under CG contained more C. elegans and C.

erecta than in the SD treatments. Lythrum californicum and

Paspalum lividum were used more in the SD than in the CG

treatments. Other species used more in the heavy treatments

were species such a R. columnaris, R. nudiflora and the grass

B. dactyloides. The grass Schizachyrium scoparium was used

extensively in the SD heavy treatment by deer during this

season (Table C.21). Cattle were using the forbs 0.dillenii

and Phyla incisa and the grass B. dactyloides in greater

proportions in the CG than in the SD treatments. The grasses

Panicum hallii and S. scoparium were used by cattle mostly in

the SD compared to CG treatments. Tridens congestus was used

66

by cattle in similar proportions in most treatments but it

was used less in the CG heavy treatment (Table C.21).

During Fall 2, cattle diets were different between SD

and CG under the moderate stocking, while in the other

treatments they were similar (Table 3.9). Deer diets were

affected by the SD under both stocking rates compared with

the CG moderate treatment (Table 3.9, Fig. 3.7). Forbs

consumed by deer during this season were C.elegans

(especially in the CG moderate = 23%), C. erecta (mostly in

the CG), L. californicum (mostly in the SD moderate), and O.

dillenii (in every treatment, but lower in the CG

moderate) (Table C22) . Cattle used Ambrosia psilostachya in

greater proportion in the SD than in the CG, while for P.

incisa, the opposite was true. Some of the grasses used by

cattle were B. dactyloides, S. scoparium (especially in the

SD treatments), S. leucotricha (higher use in the CG

treatments), and T. congestus (Table C.22).

In Winter 2, both grazing systems and stocking rates

affected deer, while stocking rates affected cattle (Table

3.9, Fig. 3.7), making their diet composition different.

Once again deer fed heavily on the patches of O. dillenii

except in the SD heavy treatment. Schizachyrium scoparium

was used by deer more in the SD than in the CG treatments,

while the sedge Cyperus acuminatus was used more in the

moderate than in the heavy treatments. This is one of the

seasons in which deer used less forbs and more browse than

67

normal, including Condalia hookeri (mostly in the heavy

treatments), Zanthoxylum fagara (mostly in the CG

treatments), and Eysenhardtia texana (mostly in the SD

treatments)(Table C.23, Figs 3.8 and 3.10). From this season

to the end of the sampling period, cattle used more grasses

and less forbs under moderate compared to heavy stocking

(Figs. 3.8 and 3.9). Cattle under the moderate stocking rate

had a level of crude protein in their diet well below their

maintenance level and 2% below crude protein values for

cattle under heavy stocking (Soltero-Gardea 1991). In terms

of plant species consumed, B. dactyloides was used more by

cattle under moderate (26%) than heavy (19%) stocking and B.

dactyloides was lower in crude protein content and

digestibility than during any other time of the study

(Soltero-Gardea 1991). Cattle doubled the amount of B.

dactyloides in their diet from Fall 2 to Winter 2 (Tables

C22 and C.23) .

Crude protein in cattle diets increased during Spring 2,

but levels were still well under the maintenance level under

moderate compared to heavy stocking (Soltero-Gardea 1991).

During Spring 2, cattle diets were different in the moderate

stocking rate compared to some of the other treatments (Table

3.9, Fig. 3.7). However, the third discriminant function

(which accounted for 5% of the treatment effects) shows that

cattle diets also were affected by grazing systems. Cattle

consumed lower amounts of forbs, in any of the treatments.

68

than the previous season (Figs 3.8). By this time of the

year the phytomass in general was very low in all treatments

(Soltero-Gardea 1991). Deer diets were not affected by any

treatment during the Spring 2 (Table 3.9, Fig. 3.7). They

increased their consumption of forbs from Winter 2 to Spring

2. Dietary crude protein content for deer increased slightly

to just above maintenance (10% crude protein)(Soltero-Gardea

1991) . Deer still were consuming O. dillenii, along with R.

nodiflora, but in the heavy treatments, they used more L.

lindheimeri. Cattle were using mostly T. congestus, S.

leucotricha, and B. dactyloides (Table C.24, Fig. 3.7).

In Summer 2, during the peak of the drought, phytomass

was at the lowest level recorded during the study, but both

deer and cattle had dietary crude protein above maintenance

(Soltero-Gardea 1991). During the Summer 2 there was a

similar effect of the grazing systems and stocking rates over

cattle diets compared to Spring 1 (Table 3.9, Fig. 3.7).

Composition of deer diets was strongly affected by grazing

systems and stocking rates (Table 3.9, Fig. 3.7). Deer had

decreased their use of forbs switching primarily to the

browse Condalia hookeri, especially under CG compared to SD

grazing (Table C.25). O. dillenii was practically gone by

this season (Fig. 3.3). The only readily available forb was

Desmanthus virgatus, which was taken by deer. B. dactyloides

was in its peak of production (Fig. 3.2) and was an important

item in cattle diet.

69 Dietary Overlap

Diet overlap between cattle and deer was minimal in Fall

1 regardless of treatment (Fig. 3.11) because deer used forbs

and browse and cattle used grasses and forbs. Highest

overlap between the diets of cattle and deer occurred in

Winter 1 and Spring 1, a time when both species were

consuming similar plant species (forbs such as A.

psilostachya, G. carolinianum, O. speciosa, O. dillenii, R.

columnaris) (Tables C.19-C20). The high degree of overlap

during Winter 2 and Spring 2 in the heavy stocking rates

compared to moderate stocking in either grazing system is

important to note (Fig. 3.11). L. lindheimeri was a forb

highly used by both deer and cattle (Tables C.23-C.24) which

probably accounted for this overlap.

Discussion

Floral Changes

Initial vegetation composition of the study area was

found to be homogeneous. Grazing treatment had no impact on

homogeneity of the plant community. There were floral

changes, but these were a product of the drought during the

second year.

Periodic drought is a characteristic of the South Texas

climate (Drawe 1985). During a drought, the forage

production can be reduced more than 50% compared to the

average annual production (Holecheck et al. 1989). The use

70

F-l W-1 SP-1 SS-1 F-2 w-2 SP-2 SS-2

Figure 3.11: Dietary overlap between cattle and deer under continuous (C) and short-duration (S) grazing systems and heavy (H) and moderate (M) stocking rates.

71

of the pastures by livestock may create problems for wildlife

because of the removal of annual growth. This combination of

a climatic event plus grazing will result in shifts,

sometimes dramatic, in species composition. Drought-

resistant species will increase at the expense of drought-

susceptible species (Pieper and Donart 1975). Such may be

the case with the observed increased of species as Oxalis

dillenii. The increase of this perennial species is directly

related to the opening of the herbage canopy, an effect of

the drought of the second year and the stocking rate.

Soltero-Gardea (1991) confirmed the findings of several other

studies where heavy stocking rates have more impact on

biomass than grazing systems. Another species that also

increased was Buchloe dactyloides, which is able to take

advantage of shallow moisture and increase vegetatively by

stolons (Chamrad and Box 1965). However, it is important to

understand that this was only the initial response to a

drought and that short-term (<2 yr) changes in the vegetation

composition did not occur because of grazing systems or

stocking rates.

Cattle and Deer Diets

The idea that deer and cattle compete for food resources

in the Texas Coastal Bend under different grazing practices

is a constant concern of ranchers and biologists. If cattle

and deer were both at high densities so as to create

72

exploitation competition, in which inhibitory effects occur

from reduced availability of a common resource (Pianka 1983,

Keddy 1989), deer would most probably be the species to

suffer most. Most sympatric species, including closely

related species such as South American camelids, will

partition their environmental resources (Franklin 1982, San

Martin and Bryant 1987). This can be achieved in three basic

ways: temporally, spatially, and trophically, which will

reduce competition allowing the coexistence of both species

(Pianka 1973). In the case of cattle/deer interactions in

the Texas Coastal Bend, these two species partition the

resource temporally by feeding at different times of the day.

Cattle usually feed regularly throughout the day, while deer

do most feeding in the early morning or evening. They also

partition the resources spatially. It has been demonstrated

that deer will move out when cattle are moved into a SD cell

(Hyde 1987, Cohen et al. 1989a and 1989b) or into HILF

pastures (Adams 1978).

Are these two animal species able to partition food

resources? There is evidence that cattle and deer have

different adaptations to herbivory. Most large herbivores,

such as cattle, are adapted to eat a variety of plants low in

digestibility and crude protein. Their rumen morphology,

relative to small herbivores, is better adapted to digest

diets containing large amounts of fiber (i.e., grasses).

Small-bodied ungulates, such as deer, require a greater

73

concentration of digestible energy. They will select more

edible and digestible diets than large ungulates (Nagy et al.

1969, Janis 1976, Kay et al. 1980, Schwartz and Ellis 1981,

Demmet and Van Soest 1983, Hobbs et al. 1983).

White-tailed deer have been classified as a ''concentrate

selector," able to use plants with a higher content of crude

protein (i.e., forbs, browse); whereas, cattle have been

classified as a ''roughage eater, " able to use plants with a

higher concentration of fibers (i.e., grasses)(Demmet and Van

Soest 1983, Hofmann 1973 and 1989). My findings supported

this: cattle ate mostly grasses, which were found to be low

in crude protein and digestibility (Soltero-Gardea 1991),

while deer used mostly forbs which were found to be high in

crude protein and digestibility (Soltero-Gardea 1991).

Grass use by cattle in this study was lower than

previous studies carried out at the Welder Wildlife Refuge.

Other researchers reported higher use of grass by cattle than

in this study (Drawe 1967, Drawe and Box 1968, Drawe et al.

1988). Everitt et al. (1981) found that the year-round diet

of cattle in the South Texas Plains (Hidalgo County)

comprised 75% grasses and only 21% forbs. In the Edwards

Plateau Region of Texas, Taylor et al. (1980) also found that

grasses were the dominant forage (above 90%) for cattle,

while forbs and browse were minor components. Similar cattle

diets were found in north-central Texas (Sanders 1975) and in

northern Mexico (Chavez 1986).

74

Higher forb use (39%) by cattle in this study should be

of some concern since it is the main forage class for white-

tailed deer in the area. In other studies cattle used high

amounts of forbs depending on the season (Lauchbaugh et al.

1990) or the grazing system used (Pitts and Bryant 1987). In

my study, there was no difference between CG and SD in the

use of forage classes by cattle. Similar findings were

reported by Sanders (1975) when comparing CG and high-

intensity low-frequency (HILF) grazing systems, or Taylor et

al. (1980) when comparing SD and Merrill grazing systems.

I found a high use of forbs by deer (range= 30 to 80%,

average = 72%) depending on the season, but Kie et al.

(1980), also working at Welder, found that deer used a higher

percentage (up to 95%, average 81%) of forbs than in this

study, although they found similar consumption of grasses.

Drawe (1967) found that deer at Welder Wildlife Refuge used

more forbs on sandy (92%) than on clay (69%) soils. On clay

soil deer use up to 40% grasses during the winter. However

during the summer deer ate more forbs (70%) than grasses

(8%), and used up to 20% browse (Drawe 1968). My study was

conducted on clay soil, which may explain the lower relative

forb consumption.

Other deer diet studies have shown that deer are more

browsers than grazers as in this study. Only 25 mi northeast

of Welder, at the Aransas National Wildlife Refuge, White

(1973) determined that deer ate up to 67% browse and less

75

than 30% forbs (most important use during mid-summer). In

comparison, deer in the Rio Grande plains (Everitt and Drawe

1974, Everitt and Gonzalez 1979) used more browse (mostly

cacti, up to 61%) than my deer in the Texas Coastal Bend.

Edwards Plateau deer also used more browse (50 to 70%) than

in the Rio Grande Plains or the Texas Coastal Bend (McMahan

1964, Bryant et al. 1979 and 1981, Waid 1983, Warren and

Krysl 1983) . Jackley (1991) found that white-tailed deer in

the Edwards Plateau Region used high amounts of forbs (up to

52%) when they were highly abundant. South-central Oklahoma

deer could shift from a high use of forbs, in spring and

summer, to browse in the fall, to browse and grasses in the

winter (Van Vreede 1987).

Deer in this study used a high variety of plant species,

depending upon the season and the treatment. Few species

were consistently used throughout the study period. Oxalis

dillenii was consistently used as it was available. However,

the similar high use of O. dillenii in every treatment may be

a reflection of selection of familiar food, perhaps a

physiological adaptation (i.e., gut flora, digestive

efficiency) (Partridge 1981). McCullough (1985) found that

the George Reserve (MI) deer ate a wide array of species in

all forage classes, showing high variation by season and

between years. This reinforces the old idea that habitat

management for deer should be directed to managing for

diversity of plant species. Deer have evolved the ability to

76

select a mix of forages that balance nutritional demands

(Vangilder et al. 1982).

The hypothesis that either grazing systems or stocking

rates could affect deer was confirmed in part by this study.

Fall deer diets were the same in most of the treatments.

During the winter deer became more selective, especially in

Winter 2, as their diets were differentially affected by the

treatments. In the spring, deer selected the same diet

regardless of the treatment where they were feeding. Summer

was critical for deer. Deer were extremely selective; their

diets were different depending upon the treatment where they

fed. In summary, deer tend to be more selective during the

summer and during drought, except for the spring months. On

the other hand, cattle were not as selective as deer during

the drought. In most of the seasons, with the exception of

Summer 1, cattle ate similar diets across all treatments.

Deer were affected by the grazing systems during Winter

1 and Summer 2 (Fig. 3.9), obtaining more forbs in the CG

than in the SD pastures. During the first two seasons of

1987 it is clear that the higher consumption of forbs by deer

in the CG resulted in them being able to maintain a dietary

crude protein above the maintenance level, especially under

CG (Soltero-Gardea 1991). I expected that deer in the SD

heavy would do better since many of the plant species are

"renewed" more often than in the CG. Evidently, repeated

77

heavy grazing followed by 3-4 weeks of rest did not "renew"

plants to render them more nutritious.

Across all treatments and periods, most important

species used by cattle were the grasses B. dactyloides, T.

congestus and S. leucotricha. Most important species for

deer were O. dillenii, C. erecta, and P. multicaulis.

However, other species were important depending upon the

the season and the treatment. Ambrosia psilostachya, R.

columnaris, L. lindheimeri, and G. carolinianum were forbs

important to cattle in different seasons under different

treatments. Some of the species important to deer, depending

on the season and treatment, were browse such as P.

glandulosa beans and Condalia hookeri, grasses such as P.

lividum and S. scoparium, and forbs such as R. nudiflora, L.

californicum, L. lindheimeri, R. columnaris, G. carolinianum,

and Desmanthus virgatus.

The highest overlap (range = 43-64%) between deer and

cattle occurred in Winter 1 and Spring 1, when deer and

cattle were consuming the forbs A. psilostachya, G.

carolinianum, O. speciosa, 0. dillenii, and R. columnaris.

These are critical periods in which both domestic and wild

ungulates tend to seek out new, rapidly growing plant species

(Mackie 1978). During the second year, significant overlap

(range = 48-64%) occurred only on pastures heavily stocked by

cattle.

78

In forested pine-hardwood, central Louisiana, Thill

(1984) found that diet overlap between deer and cattle went

from 12% in summer up to 4 6% in winter. Deer in Louisiana

are browsers (65% browse in diet) and cattle are grazers (up

to 74% grass in the diet); however, cattle can shift to

browse (up to 48%) which is the reason for the increased

dietary overlap (Thill and Martin 1986 and 1989). However, a

high degree of trophic overlap is not sufficient evidence for

competition. To demonstrate competition, data must be

obtained showing diminished health or reproduction on one of

the species involved in the interaction (Thill and Martin

1986). This aspect was outside the scope of my study.

Management Implications

The Texas Coastal Bend is an area with the potential to

produce quality deer because of high habitat diversity, a

fact of which ranchers are aware. However, periodic droughts

complicate selection of a grazing scheme that will avoid

deterioration of the habitat for livestock as well as

wildlife. To be sure, stocking rates should be carefully

monitored because dietary overlap between cattle and deer was

exacerbated under heavy stocking rates regardless of grazing

system.

In my study, I found no short-term differences in the

effect that SD or CG had on white-tailed deer diets. This

species is highly adaptable to survive and thrive under

79

adverse situations in which many other species might become

endangered. A perfect example of this is the Edwards Plateau

Region which contains one of the highest densities of white-

tailed deer in the country (Jackley 1991) in spite of the

diversity and pressure of livestock and exotic ungulates.

Planning a grazing system in the Texas Costal Bend

should take into consideration many factors, such as range

operation, economic constraints, management goals, class and

kind of livestock, wildlife and habitat management (Drawe

1985), and the high probability of having a drought. A CG

system may be the best solution, because of lower input costs

and fewer management decisions. However, only a moderate

stocking rate should be considered to avoid overgrazing

during the periods of minimal forage growth (Matches and

Burns 1985) . Overgrazing may affect wild populations more

severely than domestic livestock.

Pieper and Heitschmidt (1988) suggest that the benefits

of SD are most evident in a grazing situation characterized

by mesic environment with extended growing periods, i.e.,

conditions found in the Texas Coastal Bend. Ranchers should

also take into account that the highest deer densities and

economic returns come from grazing systems which included

systematic deferments (Reardon et al. 1978). Deer habitat

selection is highly correlated to the frequency of deferment.

Besides the initial investment in fences, which produce

problems when the ranch is leased for hunting, other

80

considerations need to be planned, such as the number of

pastures and length and frequency of grazing periods (Booysen

et al. 1974). Ranchers desiring to implement SD must be

totally dedicated to the concept (Drawe 1985), which will

improve the knowledge of the range condition, the livestock

herd, and the wildlife. My study had the limitation of a

strict 4-da/grazing, 28-da/rest and that SD treatments were

only a simulation. This reduced my ability to understand the

complexity of herbivory of these two species under the

treatments being imposed.

Most ungulates will survive even if their numbers are

lowered because of a drought. They are highly adapted to a

diverse diet that can shift during critical periods (Hansen

and Reid 1975) . However, white-tailed deer habitat should be

managed to stimulate the production of a great variety of

plant species (Vangilder et al. 1982). A rotational system

in the Texas Coastal Bend Region may accomplish that.

However, Texas Coastal Bend ranchers should be concerned

during summer, the most critical season for white-tailed

deer. There should be minimal concern about deer condition

during spring.

Further research needs to be directed to determine

reproductive success of white-tailed deer under SD and CG, as

well as to measure physiological, physical, and behavioral

aspects of this species under either grazing system. Several

authors concluded that heavy SD may remove enough grasses to

81

increase forbs, a forage highly used by deer in the Texas

Coastal Bend Region. . However, Soltero-Gardea (1991) showed

that at the beginning of a drought, desirable forbs decreased

in all systems and stocking rates. Further research

concerning synecological changes under any grazing treatment

needs to be carried out during drought, one of the most

critical periods for livestock and wildlife in the Texas

Coastal Bend Region.

82

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Van Vreede, G. 1987. Seasonal diets of white-tailed deer in south-central Oklahoma. M.S. Thesis. Tech Univ. Lubbock, TX. 84 pp.

Waid, D.D. 1983. Physiological indices and food habits of deer in central Texas. M.S. Thesis. Tech Univ. Lubbock, TX. 82 pp.

Warren, R.J. and L.J. Krysl. 1983. White-tailed deer food habits and nutritional status as affected by grazing and deer-harvest management. J. Range Manage. 36:104-109.

White, M. 1973. The whitetail deer of the Aransas National Wildlife Refuge. Texas J. Sci. 24:457-489.

Wolda, H. 1981. Similarity indices, sample size and diversity. Oecologia. 50:296-302.

CHAPTER IV

FORAGING BEHAVIOR OF TRACTABLE

WHITE-TAILED DEER

Introductinn

Foraging models need variables such as net food value

and profitability, which involve parameters such as gross

value, energy cost, eating time, digesting time, prey pursuit

and handling time (search, encounter, decision on taking or

not taking prey) (Stephens and Krebs 1986). The majority of

the work conducted in this field has considered carnivores

for which prey pursuit and handling time are important

constraints. However, for herbivores these two parameters

are irrelevant; instead eating time and digesting/processing

are the primary constraints (Owen-Smith and Novellie 1982) .

For ungulates, these parameters have been studied mostly in

livestock because it is more difficult to obtain similar data

for wild species. Time-budget/foraging behavior and foraging

models have been studied in or applied to wild ungulates such

as moose {Alces alces) (Belovsky 1978, Risenhoover 1986,

Saether and Andersen 1990), kudu {Tragelaphus strepsiceros)

(Owen-Smith and Novellie 1982), pronghorn {Antilocapra

americana), deer {Odocoileus virginianus, O. hemionus), elk

{Cervus elaphus), sheep {Ovis canadensis), and bison {Bison

bison) (Belovsky 1986, Olson-Rutz and Urness 1987) .

89

90

In comparison to omnivores, herbivores require fewer

specific nutrients since some can be synthesized (Owen-Smith

and Novellie 1982) . However, problems exist when determining

nutritional value of dietary items because plant nutrient

content will vary not only with plant phenological stage, but

also with plant parts consumed by the animal. These problems

can be solved more easily if research is directed at domestic

livestock. Determination of foraging behavioral parameters

such as distance traveled, eating rate, and bite size in wild

species is more difficult to study. For white-tailed deer,

food intake (as estimated by biting rate and bite size) has

been determined in a few studies and with tame animals only

(Crawford and Whelan 1973, Crawford 1982).

Still fewer studies have attempted to evaluate the

influence of livestock grazing practices on feeding behavior

of white-tailed deer. In particular, search strategy could

be affected although such behavior usually is dictated by

evolution and not open to modification under changing

environmental circumstances (O'Brien et al. 1990).

The objective of this study was to evaluate white-tailed

deer travel distance, grazing time, and search time under the

influence of different cattle grazing systems and stocking

rates.

91

Methods

Data were collected from December 1987 to July 1989 at

the Welder Wildlife Refuge, Sinton, Texas. The sampling

period was divided into seven seasons according to the

vegetative growing period and temperature (for further

details on seasons see Chapter III). Animal capture and

taming process are explained in detail by Ortega et al.

(1990) and Ortega (1991). Grazing treatments, animal care,

and procedures for food habits data collection are explained

in Chapter III.

On the day of the trial, four tame deer were taken to

the treatment pastures. The tractable deer followed the

observer and/or were herded toward the pastures by an

assistant. This helped prevent the deer from feeding while

in transit. When in the pre-selected treatment pasture deer

were allowed to roam freely. Thus, deer were not influenced

as to the direction of travel, except when they went to a

fence to try to move to another treatment pasture. The four

deer were each sequentially observed feeding for 25 bites to

complete a minimum of 100 bites per deer. Time in seconds

was recorded from the first to the last bite of the 25 bites

observed for each deer.

92

Data for the behavioral aspects of the study were

summarized and analyzed as follows:

(a) Search Time: total time (in minutes) recorded from

the moment deer entered the pasture to be sampled, until the

moment individuals finished feeding;

(b) Grazing Time: total time when deer were feeding

during the 100 bites observed, recorded as bites per minute;

(c) Travel distance: a pedometer was used by the

observer to record distance (m) traveled by the group of deer

while in each treatment pasture. Since the observer walked

among the group of four deer to observe feeding, it was

appropriate to consider travel distance as an average

distance for the group of animals; and

(d) Diet and Forage Diversity were calculated using the

Berger-Parker diversity index (d). To insure that the index

increased with increasing diversity, the reciprocal form

(1/d) was used (Magurran 1988).

For data analysis, I used the statistical model of a

split-plot in time ANOVA (SAS 1985, Ott 1988) (Tables D.l-

D.3). For analysis of the diet and forage diversity, the

Kruskal-Wallis test was used (Ott 1988). Correlation and

regression analysis was conducted to establish relationships

among the different parameters obtained (Ott 1988).

93

Predictions

I expected the following:

1. As search time increases, grazing time should decrease.

The animal has little time to feed because of using its

time searching for more profitable food. While search

time should increase as travel distance increases, diet

and forage diversity also should increase. This may be

the case in a more homogeneous plant community compared to

a patchy community. This would be the case in which

animals eat what is available during the search pass,

without stopping for the more palatable/profitable food

item.

2. As diet and forage diversity decreases, grazing time and

travel distance should increase. In this example, the

animal has found a patchy environment in which there are

more palatable/ profitable food items on which it will

spend more time feeding.

Results and Discussion

There was no difference (p>0.05) in white-tailed deer

foraging behavior among grazing systems or stocking rates

(Table 4.1, Tables D.1-D.3). This agrees with the idea by

O'Brien et al.(1990) that search behavior will not be

modified by changes in the environment, i.e., grazing

practices in my study.

94 Table 4.1: Foraging behavior of white-tailed deer

under different grazing treatments averaged across all seasons. (SD = short-duration grazing, CG = continuous grazing; means with the same superscript within stocking rates or grazing systems are not significantly different (P>0.05)).

Foraging Behavior

Stocking Rate

Heavy Moderate

Grazing System

SD CG

Search Time (minutes)

68.8 a 69.4 39.9 ^ 37.4

Grazing Time (bites/min)

38.9 a 38.5 a 67.3 ^ 70.9 ^

Travel Distance (meters)

973.0 a 995.5 984.1 3 984.5 ^

95

There were highly significant differences (P<0.001) in

foraging behavior among seasons (Table 4.2, Tables D.l -

D.3) . Deer had the longest search time during Winter 1,

progressing to shorter search time during seasons of the

second year (Table 4.2). Effect of season on travel distance

was similar to results of search time: the longest distance

traveled by deer was during Winter 1; shorter distances were

traveled during the second year (Table 4.2). A possible

explanation relates to "lack of knowledge" of the area by the

deer, which kept them longer in the pastures while searching

for food items. The more familiar the animals became, the

shorter time they spent searching and the shorter distance

they traveled to find food, which most of the time was found

in patches, especially, patches of Oxalis dillenii.

The longest grazing time by deer was recorded during

Spring 2, Winter 2, and Fall 2; grazing time was shortest

during Winter 1 (Table 4.3). The more time deer spent

searching for food the less time they spent feeding, which

accounts for the shortest grazing time during Winter 1.

There were differences in diversity of vegetation and

deer diets under the different treatments and throughout

seasons (P<0.05) (Fig. 4.1). Although these differences

existed, I still used these data to test some of my

predictions.

Several of my predictions were confirmed, i.e., when

search time increased grazing time decreased (r = -0.91,

96

p c CD

I - P M O

(D CO cp cp II - H

J-l ^ 0) CO -O P C P

o p (U

-P M - H cd

P CU

> i >

0) -P

 i X l

CO cp II O iT>

C X U - H O N "

- H CO CO > M CU CO O -P

^ — CO i en g U (0 4-> O M CO - P

(U CO P

- P - ^ M G CO Cn O

C ^--^ O - H -P CO N CO (0 fO >-• 0) >-

M E H

CO CD - P - H

CD 6

•ri E H

Cn C

• H N fCj M

CO CD - p

- H

CD

- H EH

o M (C <D

CO

CO

CO

CO

X CO

X CJ

CO

CO

o (0 (0 CD CO

r-^ • ^

o • ^

o

•a* CN CNI

i n CNJ U3

CO r-to

o VD <X>

O O 00

oo o

o 00 o CNJ

n in

CO

m

ro

ro

00

i n

in

*^

o

o o Cvj

o CN

i n

CN

VD

in

VD in

CN

o VD

o

oo CN 00

CN r-o

CN

00

in

o VD

cy>

VD VD

CNJ

C3 VD

O 00

o VD

CTl

00

OO C~-

CN

CN

cr>

oo

00 00

o o VD

O VD in

00

in

VD

CTV

oo

00

CN OO

CN

o CN VD

O VD VD

O oo VD

i n

CN

C\J CT>

CT> CTl

VD

ro CTi

o ro

CN

o o oo

o VD VD

O CN

oo

r-ro

cr> i n

^ VD

cy> oo

CN CT>

r-oo

CN r-

cy>

VD

o

rH

in r-

ro ro

o •^

in ^

^ ro

^ 00

a\ CN

00 oo

o VD i n

00 ^

Ovj • ^

o 00

r-\ OO

CTi CN

CTi CvJ

X U

CN i n

^ •^

en 00

o 00

CTv CN

CTi CN

O 00

CN

u CD j j c;

• H IS

0^ C

• H M On CO

M

^ H g 13

CO

CsJ

^ -H (0 t ,

M CD 4-) G

• H S

tn C

- H M

a CO

M CD c g d CO

Table 4.3 Seasonal travel distance, search time, and grazing time of white-tailed deer across grazing treatments. (Values with different superscripts within columns are significantly different P<0.001)

97

Season

Winter

Spring

Summer

Fall 2

Winter

Spring

Summer

1

1

1

2

2

2

Search

Time

(minutes)

56

42

42

32

31

29

31

a

b

b

c

c

c

c

Grazing

Time

(bites/minute)

41.6

60.1

60.9

84.3

86.9

93.2

71.6

d

c

c

a

a

a

b

Travel

Distance

(meters)

1621 a

1189 ^

1154 b

701 c

556 c

655 c

745 c

98

winter 1 Spring 1 Summer 1 Fall 2 Winter 2 Spring 2 Summer 2

• CH [~] CM HI SH n SM

Winter 1 Spring 1 Summer 1 Fall 2 Winter 2 Spring 2 Summer 2

Figure 4.1: Seasonal diversity indices (1/d) for (a) vegetation of different treatments and (b) deer diets. The higher the index number the greater the diversity. (C = continuous grazing, S = short-duration grazing, H = heavy stocking rate, M = moderate stocking rate).

99

Fig. 4.2.a) and travel distance increased (r = 0.92, Fig.

4.2.b). Evidently, deer traveled longer distances searching

for food without stopping to eat. Even though there was no

relationship between diet diversity and search time, the

greater the diversity of plant species affected search time.

Thus, the more "decisions" the deer may have had to make to

obtain the most profitable food, the greater the increase in

its searching time (Fig. 4.2.d). Thus, the theory that

animals spend more time searching for food in a more diverse

environment was found to be true for white-tailed deer in

this study (r = 0.68, Fig. 4.2.d).

As animals spend more time searching for highly

palatable/profitable food, diet diversity should be higher.

This was not found to be true in this study (r = 0.07, Fig.

4.2.C). This may be related to the fact that white-tailed

deer are concentrate selectors (Hofmann 1985). Thus deer

take fewer species than offered by the environment and spend

more time on certain species to achieve the greatest

concentration of dietary nutrients.

Because white-tailed deer are concentrate selectors, a

determined number of species (highly palatable/profitable

ones) may be necessary to support deer in an area. A highly

correlated cubic polynomial regression shows that a forage

diversity index between 8 to 10 may be necessary to make the

area suitable for deer (Fig. 4.3.a).

100

B -H EH

Cr« C

-H N CO P o

1 ?R —1

1 0 0 -

7 5 -

5 0 -

9 R Z O

r^ = 0 .

•

N*%

1

83

\s

1

r =

1

- 0 . 9 1

•

1

r ^ = 0 .84 r = 0 . 92

20 30 40 50 60 70

S e a r c h Time (min.) Search Time (min.)

r = 0.07 :2 = 0.47 r = 0.68

20 30 40 50 60 70

Search Time (min.)

n 14

20 30 40 50 60 70

S e a r c h Time (min. )

Figure 4.2: Plot of regression lines for search time (min.) versus (a) grazing time (bites/min.), (b) travel distance (m), (c) diet diversity and (d) forage diversity (1/d) for white-tailed deer across all different grazing treatments. Coefficient of determination (r ) and correlation coefficient (r) are given above each graph.

101

XJ 14

20 30 40 50 60 70

S e a r c h Time (min.)

2400 r ^ = 0 . 7 9 r = - 0 . 8 9

20 40 60 80 100 120

G r a z i n g Time (b/m)

20 40 60 80 100 120


• 7 ^ 1 A

I-H

' - ' 1 2 -> 1

tl 10-•H CO ^ ft-(U ° >

<1> , Cr> 4 -cO P

r 2 =

• •

1

0

•

.39

• • •

•

•

• Vv

• ^

• • •

fl

1

r

c »

1

= - 0 . 6 2

• •

" ^ ^ • >^^

1 1 UA 20 40 60 80 100 120


Figure 4.3: Plot of regression lines for (a) Search time (min.) versus forage diversity (1/d); grazing time (bites/min) versus (b) travel distance (m), (c) diet diversity, and (d) forage diversity (1/d) for white-tailed deer across all grazing treatments. Coefficient of determination {T2) and correlation coefficient (r) are given above each graph.

102

As grazing time increased, white-tailed deer travel

distance decreased (r = -0.89, Fig. 4.3.b). This behavior was

related to a patchy environment in which deer stopped at a

patch and spent time grazing before moving on to another

patch. As grazing time increases, diet diversity should

decrease, especially in a patchy situation. Thus, deer would

stop at a patch and spend some time there before moving on to

another area. This relationship was not found (r = -0.17,

Fig 4.3.C), suggesting that deer may be going from patch to

patch feeding on several species within each patch without

concentrating on only one or few species, unless they found a

patch that contained one highly palatable/profitable species

(e.g., Oxalis dillenii) . — _- . .

As forage diversity decreased grazing time increased

(r = -0.62, Fig. 4.3.d). Again, this was related to a patchy

environment. The fewer the species in the area, the greater

the amount of one species that might be found. Thus when

deer found those patches (e.g., Oxalis dillenii), they were

highly fed upon and had a higher represention in the diet.

Conclusions

Foraging behavior in deer was unchanged regardless of

grazing system or different stocking rate, but there were

differences among seasons. I observed that as search time

increased grazing time decreased while travel distance

increased. It seems that a forage diversity of about 8 to 10

103

will make a suitable habitat for deer because it is at that

diversity that deer search time levels off. I also observed

that as forage diversity decreased grazing time increased;

and when grazing time increased, travel distance decreased.

This may be related to a patchy environment with highly

palatable/profitable species found in those patches.

Further studies need to be conducted to determine

parameters such as bite size to be able to classify deer

under Schoener's (1971) feeding strategies of time-minimizer

vs energy-maximizer. Belovsky (1986) has classified white-

tailed deer as energy maximizers (the animal maximizes the

amount of energy gained in a fixed time). This could be true

in the deer that I studied. In the case of the Texas Coastal

Bend, deer must be adapted to very high temperatures most of

the day from April to October, which may limit the time for

grazing to nighttime or at sunrise/sunset. Thus, deer should

maximize the amount of energy gained within that period.

104

Literature Cited

Belovsky, G.E. 1978. Diet optimization in a generalist herbivore: the moose. Theor. Pop. Biol. 14:105-134.

Belovsky, G.E. 1986. Optimal foraging and community structure: implications for a guild of generalist grassland herbivores. Oecologia. 70:35-52.

Crawford, H.S. 1982. Seasonal food selection and digestibility by tame white-tailed deer in central Maine. J. Wildl. Manage. 46:974-982.

Crawford, H.S. and J.B. Whelan. 1973. Estimating food intake by observing mastications of tractable deer. J. Range Manage. 26:372-375.

Hofmann, R.R. 1985. Digestive physiology of the deer — their morphophysiological specialization and adaptation. Royal Soc. New Zealand Bull. 22:393-407.

Magurran, A.E. 1988. Ecological diversity and its measurements. Princeton Univ. Press. Princeton, NJ. 17 9 pp.

O'Brien, W.J., H.I. Browman, and B.I. Evans. 1990. Search strategies of foraging animals. Amer. Sci. 78:152-160.

Olson-Rutz, K.M. and P.J. Urness. 1987. Comparability of foraging behavior and diet selection of tractable and wild mule deer. Utah Div. Wildl. Res. Pub.No 88-3. 3 9 pp.

Ortega, I.M. 1991. Taming captive-born and wild-born white-tailed deer fawns. Texas J. Sci. 43:215-217.

Ortega, I.M., L.D. Perry, D.L. Drawe, F.C. Bryant. 1990. Observations on obtaining white-tailed deer fawns for experimental purposes. Texas J. Sci. 42:69-72.

Ott, L. 1988. An introduction to statistical methods and data analysis. Third Edition. PWS-KENT Pub. Co. Boston. MA. 835 pp.

Owen-Smith, N. and P. Novellie. 1982. What should a clever ungulate eat? Amer. Nat. 119:151-178.

Risenhoover, K.L. 1986. Winter activity patterns of moose in interior Alaska. J. Wildl. Manage. 50:727-734.

105 Saether, B. and R. Andersen. 1990. Resource limitation in a

generalist herbivore, the moose Alces alces: ecological constraints on behavioural decisions. Can. J. Zool. 68:993-999.

SAS. 1985. SAS User's Guide: Statistics, Version 5 Edition. SAS Institute Inc. Gary, N C 956 pp.

Schoener, T.W. 1971. Theory of feeding strategies. Ann.Rev. Ecol. Syst. 2:369-403.

Stephens, D.W. and J.R. Krebs. 1986. Foraging theory. Princeton Univ. Press. Princeton, NJ. 247 pp.

APPENDIX A

PLANT SPECIES COMMON AND SCIENTIFIC NAMES

106

Table A.l 107

Common and scientific names of forbs used by deer and cattle at the Welder Wildlife Refuge, Sinton, TX, 1987-1989.

COMMON NAME SCIENTIFIC NAME

Fern acacia

Western Ragweed Marsh Parsley

Low wildmercury

Sump aster

Chervil

Widow's tears Golden Wave Prairie tea Dodder Bundle flower Eryngo Prostrate euphorbia Spurge Carolina geranium Blue morning-glory Sumpweed Bladderpod

Loosestrife

False mallow

False mallow

Pepperwort

Bur-clover Powderpuff Horsemint False garlic Pink Evening Primrose Wood-sorrel Phlox Sawtooth Frogfruit Spatulate Frogfruit Leaf-flower

Acacia angustisima (Mill.) Ktze.* Agalinis heterophylla (Nutt.) Small Ambrosia psilostachya DC. Apium leptophyllum (Pers.) F. von

Muell. Argythamnia humilis (Engelm, & Gray)

Muell. Arg. Aster subulatus Michx. Brazoria scutellarioides Engelm. &

Gray Chaerophylum tainturieri Hook. Commelina elegans H.B.K. Commelina erecta L. Coreopsis tinctoria Nutt. Croton monanthogynus Michx. Cuscuta spp. Desmanthus virgatus (L.) Willd. Eryngium hookeri Walp. Euphorbia prostrata Ait. Euphorbia spathulata Lam. Geranium carolinianum L. Ipomoea hederacea Jacq. Iva annua L. Lesguereiia lindheimeri (Gray) Wats. Limnosciadium pumilum (Engelm. &

Gray) Math. & Const. Lythrum californicum Torr. & Gray Machaeranthera tenuis (Wats.) Turner

& Home Malvastrum aurantiacum (Scheele)

Walpers Malvastrum coromandelianum (L.)

Garcke Marsilea macropoda A.Br. Maximalva filipes (Gray) Fryxell Medicago polymorpha L. Mimosa strigillosa Torr.& Gray Monarda punctata L. Nothoscordum bivalve (L.) Britt. Oenothera speciosa Nutt. Oxalis dillenii Jacq. Phlox drummondii Hook. Phyla incisa Small Phyla nodiflora (L.) Greene Phyllanthus polygonoides Spreng.

Table A.l: Continued lOS


False dandelion Prairie coneflower Little snoutbean Dewberry Clay violet Meadow Pink Ragwort Spreading Sida Silverleaf nightshade Sow thistle Green-thread Brush Noseburn Frostweed Purple Vetch Annual Broomweed

Phyrrhopappus multicaulis DC. Ratibida columnaris (Sims) D.Don. Rhynchosia minima (L.) DC. Rubus trivialis Michx. Ruellia nudiflora (Gray) Urban Sabatia campestris Nutt. Senecio imparipinnatus Klatt Sida filicaulis Torr. & Gray Solanum elaeagnifolium Cav. Sonchus spp. Thelesperma filifolium (Hook.) Gray Tragia brevispica Englm. & Gray Verjbesina microptera DC. Vicia leavenworthii Torr. & Gray Xanthocephalum dracunculoides (DC.)

Shinners

* Follows taxonomy of Jones, F.B. 1982. Flora of the Texas Coastal Bend. Welder Wildlife Foundation. Mission Press, Corpus Christi, TX. 267 pp.

Table A.2. 109

Common and scientific names of grasses and sedges used by deer and cattle at the Welder Wildlife Refuge, Sinton, TX, 1987-1989.

COMMON NAME

Winter bentgrass Prairie threeawn Silver bluestem Rescue grass Buffalo grass Sedge Bermuda grass

Kleberg bluestem Angleton bluestem

Spikerush Plains lovegrass Little barley Bunch cutgrass Nimblewill Filli panicum Halls panicum Vine mesquite Rustyseed paspalum Longtom

Carolina canarygrass Little bluestem

Bulrush Knotroot Meadow dropseed Winter grass White tridens

Pink tridens

SCIENTIFIC NAME

(Forsk.) Stapf (Poir.) C E .

(L.) R.& S.

Agrostis hiemalis (Walt.) B.S.P.* Aristida oligantha Michx. Bothrichloa saccaroides Rydb. Bromus willdenowii Kunth. Buchloe dactyloides (Nutt.) Engelm. Carex brittoniana Bailey Cynodon dactylon (L.) Pers. Cyperus acuminatus Torr.& Hook. Cyperus articulatus L. Cyperus haspan L. Dichanthium annulatum Dichanthium aristatum

Hubb. Eleocharis acicularis Eleocharis montevidensis Kunth. Eragrostis lugens Nees. Hordeum pusillum Nutt. Leersia monandra Swartz. Muhlenbergia schreberi Gmel. Panicum filipes Scribn. Panicum hallii Vasey. Panicum obtusum Hitchc. & Chase. Paspalum langei (Fourn.) Nash. Paspalum lividum Trin. Paspalum sp. Phalaris caroliniana Walt. Schizachyrium scoparium (Michx.)

Nash Scirpus saximontanus Fern. Setaria genlculata (Lam.) Beauv. Sporobolus asper (Michx.) Stipa leucotricha Trin. Tridens albescens (Vasey)

Standi. Tridens congestus (L.H.Dewey) Nash

Kunth.

Woot

* Follows taxonomy of Gould, F.W. and T.W. Box. 1965. Grasses of the Texas Coastal Bend. Texas A&M University, Collegue Station, TX. 186 pp.

Table A.3 110

Common and scientific names of browse species used by deer and cattle at the Welder Wildlife Refuge, Sinton, TX, 1987-1989.


Blackbrush acacia Huisache Huisachillo Agarito Chittimwood Sugar hackberry Granjeno Brasil Texas persimmon Kidneywood Tanglewood Berlandier wolfberry Honey Mesquite Creeping Mesquite Colima Lotebush

Acacia rigidula Benth.* Acacia smallii Isely Acacia scaffneri (Wats.) Herm. Berberis trifoliolata Moric. Bumelia lanuginosa (Michx.) Pers. Celtis laevigata Willd. Celtis pallida Torr. Condalia hookeri M.C Johnst Diospyros texana Scheele Eysenbardtia texana Scheele. Forestiera angustifolia Torr. Lycium berlandieri Dunal Prosopis glandulosa Torr. Prosopis reptans Benth. Zanthoxylum fagara (L.) Sarg. Ziziphus obtusifolia (T.&G.) Gray

* Follows taxonomy of Jones, F.B. 1982. Flora of the Texas Coastal Bend. Welder Wildlife Foundation. Mission Press, Corpus Christi, TX. 267 pp.

APPENDIX B

ANALYSIS OF VARIANCE TABLES

111

112

-P G P O O I

(U -p -H aO

G - H p CO

o o G (U

,G 15

CO

Xi u o ip

> i p CO

4-> 0)

-H

-o CO P O

cp P +J CO

 >

i p

o CO

- H CO > 1

i H CO G <

CO aG 0^ O CO 

PQ

(U

rH aO CO EH

-P CO (U EH

0 P

tH CO > I

CU

IM

CO CN

CO

VD CN

O CN

rH 00

58

7.

rH O

CNI

O 00

'=r

o

28

6

VD i n

CTv

in

en

r-\

in in

CO T H

VD

CN TH

CO CO

t 4

 G o s -K

x u (U H •K

a (U pc

C30 O tH O

•

o

00

o o

•s^ in o CN

x^ o G O

-K aG

o CU

EH

O CN

P G O

-K

u CU

EH -K a <u

pc:

113

 - H aQ

Cn G

- H P CO a B o u G 0

aG >

CO 

> i P CO 4-J (U

- H

-o P O

i p



m o CO

- H CO

• CO

rH P 4-1 CO

-H cp

H CO 

>1 4-) rH CO G <

CN

PQ

CU H aQ CO

EH

G p O O

4-> CO 0

E H

0 P

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APPENDIX C

FORMULAE AND RAW DATA OF CATTLE AND DEER

FOOD HABITS UNDER DIFFERENT GRAZING

STRATEGIES

115

c.l. Formulae for F ratios for the Mahalanobis distance between each pair of groups*

F = (Ji + "2 - P - 1) ^ (ni * n ) ^ 2 (n + n2 - 2) (n + n2) * ° "

where ni = number of samples in group 1

n2 = number of samples in group 2

p = total number of groups (in our case 8: 4

treatments * 2 species)

D^M = pairwise distance within groups.

d.f. are determined by the formulae = ni + n2 - p - 1.

116

*(after Lindeman et al. 1980)

117 C 2 . Formulae for Morosita-Horn similarity index*

where

211 {an • * bn •) • MH ~ " •—

{da + db)aN * bN

aN - total percent of diet in esophageal fistula

method,

bN = total percent of diet in bite-count method,

in this case 100 for either aN or bN,

ani = the percent of diet in the 1 th plant species

in esophageal fistula method,

bn± = the percent of diet in the i th plant species

in bite-count method.

2 2

Dan. Zbn . da = and db =

2 2

aN bN A C MH of 100 would result if the two methods were identical

* (after Magurran 1988)

118

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p CO •K

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CD P to

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to

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to Q)

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u CD •K

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Table C.18: Cattle and deer diet composition (%) under continuous (C) and short-duration (S) grazing systemb, and heavy (H) and moderate (M) stocking rates during Fall 1. (Species with a relative frequency >2% in any of the treatments, T=trace)

CATTLE DEER

S M CM S H C H S M CM S H C H

F o r b s

Ambrosia psilostachya 1.7 1.6 1.6 5.6 0.5

Commelina elegans 1.4 3.2 1.1 2.2

Commelina erecta 6.9 25.1 3.0 36.5

Croton monanthogynus

Iva annua

3.1 8.0 5.9 3.2

10.1 7.2 7.9 12.4

0.3 2.0

0.2 0.7

Lythrum californicum 1.0 1.8 0.1 2.5

Malvastrum aurantiacum 9.6 8.0 7.9 9.5 3.3 1.1 2.0

Marsilea macropoda 2.2 1.1 2.6 2.6 0.1 0.4

Phyla incisa 0.3 3.8 0.3 2.6 0.8 1.5

Phyla nodiflora 0.1 0.1 0.2 3.2

Ratibida columnaris 15.4 12.2 9.5 13.6 1.0 0.7

Ruellia nudiflora 1.8 0.6 1.4 7.7 10.7 6.1 13.3

Xanthocephalum dracunculoides 0.3 1.3 0.1 4.3

Grasses and Seciges

Bothrichloa saccaroides 3.2 0.8 4.4 3.6

Buchloe dactyloides 20.8 18.6 17.5 18.1 2.9 1.3 1.3

Cynodon dactylon 0.3 2.8

Cyperus acuminatus 11.7 1.2 0.5

Table C.18: Continued.

CATTLE

S M CM S H C H

134

DEER

S M CM S H C H

Dichanthium annulatum

Leersia monarda

Paspalum lividum

Schizachyrium scoparium

Setaria genlculata

Sporobolus asper

Stipa leucotricha

Tridens congestus

2.5 0.2 3.2 0.7

1.8 8.2 1.6 2.4

0.7 0.6 2.6 0.5

4.0 1.2 7.6 0.5

0.7 0.8 1.1 0.2

1.6 7.5 3.6 1.8

0.5 2.1 0.6 1.0

11.7 8.4 14.9 5.1

16.4

9.0

0.7

19.0

3.1

5.0 0.2

0.3

Browse

Celtis laevigata

Condalia hookeri

Diospyros texana

Eysenhardtia texana

Prosopis glandulosa

Zanthoxylum fagara

0.1

2.1 1.3 4.8

6.3 5.3 3.1 8.2

4.9 3.3 1.1 2.2

2.7 0.7 12.2 6.6

7.6 35.4 25.0 5.6

0.9 10.7 1.1 6.7

135 Table C.19: Cattle and deer diet composition (%) under

continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Winter 1. (Species with a relative frequency >2% in any of the treatments, T=trace)

CATTLE DEER


F o r b s



Jva annua 1.7 2.2 1.5 2.6 0.1 0.1 - 0.1

Lesquerella lindheimeri 1.8 6.7 3.0 3.7


Machaeranthera tenuis 1.9 0.1 2.0 0.3 0.2 0.4


Marsilea macropoda 2.4 1.8 2.6 2.4

Phyla incisa 1.1 3.0 0.9 4.7

Phyrrhopappus multicaulis 0.2 T 0.6 0.3 14.8 21.7 14.1 13.0


Ruellia nudiflora 0.4 T 0.1 T 2.2 0.6 2.2 0.6

Xanthoc ephalum dracunculoides 5.7 2.5 2.1 7.1 0.3 1.3 0.9 2.5

Grasses and Sedges

Bromus willdenowii 5.6 10.8 8.5 4.2


Cynodon dactylon 1.8 0.5 2.1 0.5 1.6 0.2 3.5

Cyperus acuminatus 0.3 1.1 0.2 0.8 4 .0 0.2 0.7 0.3

Table C.19: Continued. 136

CATTLE

Muhlenbergia schreberi

Paspalum lividum

Schizachyrium scoparium

Sporobolus asper

Stipa leucotricha

Tridens congestus

S M C M S H C H

2 . 5 2 . 3 1 .4 2 . 2

1 .7 0 . 3 2 . 5 0 . 7

2 . 5 0 . 9 4 . 3 0 . 5

4 . 0 1 .8 3 . 5 3 . 1

3 . 0 4 . 9 2 . 3 4 . 9

1 0 . 7 7 . 9 9 . 1 6 . 1

DEER

S M C M S H C H

8 . 6 8 . 1 9 . 4 1.4

3 .5 9 . 5

0 . 1

B r o w s e

Condalia hookeri

Eysenhardtia texana

Zanthoxylum fagara

0.0

0.1

1.0 2.0 2.6 1.2

0.8 0.3 1.9 3.0

0.5 0.6 2.2 4,8


continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Spring 1. (Species with a relative frequency >2% in any of the treatments, T=trace),

CATTLE DEER


F o r b s




Lythrum californicum 0.3 0.4 0.3 T 12.5 4.8 8.1 3.1

Malvastrum aurantiacum 2.0 2.2 3.6 1.4 0,7 1.7 1.1 0.1


Oxalis dillenii 3.5 8.7 3.0 7.5 4.4 7.9 3.4 3.2

Phyrrhopappus multicaulis 0.3 1.0 0.5 0.9 22.9 9.1 23.2 18.4



Grasses and Sedges




Hordeum pusillum 4.3 3.5 5.5 4.6 3.5 4.2 4.1 0.2

Schizachyrium scoparium 0.9 0.2 1.9 0.2 1.6 0.2 3.3

Stipa leucotricha 1.3 1.7 2.3 1.4 0.1

Tridens congestus 11.9 6.9 10.1 6.1


CATTLE DEER

S M C M S H C H S M C M S H C H

Browse

Celtis laevigata 0.4 0.1 0.6 0.2 2.0

Diospyros texana 0.6 2 0.3 2.8


continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Summer 1. (Species with a relative frequency >2% in any of the treatments, T=trace).

CATTLE

S M CM S H C H

DEER

S M CM S H C H

F o r b s


Commelina elegans 0.3 1.2 0.3 1.5 5.3 0.7 6.2

Commelina erecta 3.2 3.7 1.8 4.5 4.6 11.1 3.8 11.3

Desmanthus virgatus 0.6 0.1 0.7 0.4 9.2 9.5 8.3 9.4



Mimosa strigillosa 0.1 0.1 0.1 2.9 1.4 3.4 2.2


Oxalis dillenii 1.7 3.1 1.5 4.4 31.1 30.2 26.1 26.8

Phyla incisa

Ratibida columnaris

2.6 5.8 3.2 5.0

3.3 4.2 3.6 3.6

0.8 2.5 0.9 2.2

0.8 1.6 2.8 2.5

Ruellia nudiflora 1,4 1.3 2.0 1.8 7.5 6.1 8.0 7.8

Grasses and Sedges

Agrostis hiemalis

Bothrichloa saccharoides

Buchloe dactyloides

Cynodon dactylon

2.8 1.2 1,4 1.2

2.4 1.2 2.8 0.8

17.5 19.9 16.2 22.1

1.1 1.7 1.2 1.1

1.8 3.4 2.0 3.4

0.5 1.4 2.5 2.4

Dichanthium annulatum 2.3 2.8 2.6 3.5

Muhlenbergia schreberi 2.1 2.7 1.7 1.0 0.1 0.2


Browse

CATTLE DEER

S M CM S H C H S M C S H C H

Panicum hallii 2.1 0.9 3.0 1.2 0.2 0.1

Paspalum langei 1.2 0.2 2.1 0.3




Tridens congestus 19.3 17.4 15.4 13.9 0.3 T

Celtis laevigata 0.1 0.1 0.7 0.9 2.3 1.9

Diospyros texana 0.1 0.6 0.2 0.6 1.5 2.6 1.2

Prosopis glandulosa 0.1 0.1 0.2 1.3 3.1 3.1 1.8


continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Fall 2. (Species with a relative frequency >2% in any of the treatments, T=trace)

Grasses and Sedges

CATTLE DEER


F o r b s


Commelina elegans 0.3 4.2 0.4 1.3 2.7 23.0 1.5 6.1


Desmanthus virgatus 0.1 0.1 0.6 0.7 2.4



Machaeranthera tenuis 0.1 0.3 1.3 1.1 2.3 1.3


Mimosa strigillosa 2.3 1.4 0.8 0.1


Oxalis dillenii 4.8 7.3 3.1 3.0 20.9 12.1 18.0 17.8

Phyla incisa 3.5 4.8 2.3 9.4 1.6 2.4 1.4 1.8

Phyla nodiflora 0.2 0.1 T 0.2 0.8 0.6 4.0 10.8



Solanum elaeagnifolium 0.1 0.8 2.7 3.4

Bothrichloa saccaroides 1.8 1.1 2.0 0.7 1.2 0,2 0.2


T a b l e C .22 : C o n t i n u e d . 142

CATTLE

S M CM S H C H

DEER

S M CM S H C H

Cynodon dactylon

Cyperus acuminatus

Dichanthium annulatum

3.8 3.0 1.2 2.0

0,1 0.6 0.3 0.6

6.4 2.6 2.5 3.8

0.3 0.6 0.5 0.1

1,2 1.5 2.0 0,7

0,2

Muhlenbergia schreberi 0.8 1.3 0.9 2.3

Paspalum lividum 1.2 0.3 0.5 0.5 3,2 0.4 2.4 1.3

Schizachyrium scoparium 6.3 0.7 8.9 0.8 7.5 6.3


Tridens congestus 9.5 7.9 8.3 8.4

Browse

Celtis laevigata

Eysenhardtia texana

Zanthoxylum fagara 0.1

1,7 2,8 4,7 0,4

1,2 3.2 0.5

1.1 3.8 3.6 8.4


continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Winter 2. (Species with a relative frequency >2% in any of the treatments, T=trace).

CATTLE

S M CM S H C H

DEER

S M CM S H C H

F o r b s






Oenothera speciosa 0.1 0.2 2.3 1.5 2.0 2.6

Oxalis dillenii 1.2 0.5 1.2 1.6 22.0 24.0 5.6 17.9

Phyla incisa 5.7 9.4 7.8 7.9 0.4 1.9 0.5 1.0

Ratibida columnaris 3.0 2.9 4.5 7.0 2.7 8.8 5.9 5,8

Ruellia nudiflora 0.2 0.1 0.8 0.6 1.7 3.5

Solanum elaeagnifolium 0.5 0.3 1.0 2.1

Grasses and Sedges


Carex brittoniana 1.5 1.0 2.1 1.8

Cynodon dactylon

Cyperus acuminatus

2.0 2.6 1.7 1.6

0.2 0.1 0.2 0,3

0.1 - - 0.2

7.2 6.6 3.5 1.3


Schizachyrium scopari

Stipa leucotricha

urn 5.8 0.8 3.9 0.2

19.6 22.1 14.8 17.3

5.9 0.1 8.3

1.3 0.5 2.5 3.0


CATTLE DEER

Browse


Tridens congestus 9.4 8.2 7.8 7.2 0,3

Celtis pallida 1.1 3.5 5,2 4,5

Condalia hookeri 0.8 0.1 3.3 9.8

Eysenhardtia texana 7.8 3.8 9.7 0,9

Zanthoxylum fagara 2.5 14.5 4.4 8.4


continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Spring 2. (Species with a relative frequency >2% in any of the treatments, T=trace)

Grasses and Sedges

CATTLE DEER


F o r b s


Commelina elegans 0.0 0.6 0.9 0.1 5.3 1.0 1.3

Commelina erecta 0.4 1.5 0.2 1.5 3.7 2.4 7.5



Lythrum californicum 0.1 0.6 0.1 0.9 3.4 2.2 2,5 2.1

Malvastrum aurantiacum 2.8 4.1 4.0 3.3 3.6 7.3 3,6 4.2

Mimosa strigillosa 0.9 0.9 2.0

Oenothera speciosa 0.1 0.0 0.1 6.2 1,1 3,2 1.6

Oxalis dillenii 2.4 1.0 2.3 4.9 38.8 31.9 26.2 35.3

Phyla incisa 1.2 1.7 1.9 2.2 0.2 1.3 2.2

Ratibida columnaris 3.5 2.6 4.9 3.0 4.6 7.5 6.6 1,7

Ruellia nudiflora 1.0 0.8 0.8 1.6 8.5 11.6 13.3 5,8



Cynodon dactylon 1.7 2.9 0.8 3,0

Cyperus acuminatus 1.3 0.1 0.1 0.4 2.1 2,0 1,7 0,6



Browse

CATTLE DEER

S M C M S H C H S M CM S H C H


Sporobolus asper 0.3 2.0 0.6 0.6


Tridens congestus 17.0 13.2 13.1 9.1 0.2

Celtis laevigata 1.6 0.3 3.8

Condalia hookeri 0.2 0.6 2,6

Zanthoxylum fagara 0,2 0,3 0.3 3.5


continuous (C) and short-duration (S) grazing systems, and heavy (H) and moderate (M) stocking rates during Summer 2, (Species with a relative frequency >2% in any of the treatments, T=trace).

Grasses and Sedges

CATTLE DEER


F o r b s

Argythamnia humilus 2.1 1.4 3.2 2.2

Commelina elegans 0.8 0.2 1.4 1.3 1.9 12.0



Lesguereiia lindheimeri 2.7 2.9 4.8 2.3

Lythrum californicum 0.6 1.4 0.8 4.1 0.6 0.2

Malvastrum aurantiacum 2.7 5.5 4.2 4.7 1.7 1.0 3,7 3.7

Mimosa strigillosa 0.1 0.1 0.4 0.1 6,3 5,1 0,8

Oxalis dillenii 0.4 0.1 0.3 0.2 4.1 1.6 5.6 1.8

Phyla incisa 2.6 3.1 6.8 3.6 3.3 5.0 3.4 3.0

Phyla nodiflora 0 .7 2 . 8 1.4 2 . 8 2 . 0 7 . 8 4 . 2 0 . 3

i^ue i i ia nudiflora 2.9 2.7 3.7 3.2 11.2 9.5 8.0 7.1

Agrostis hiemalis 2.3 0.8 0.4 0.4


Cynodon dactylon 1.3 1.8 1,4 1.5 1.2 7.5 0.1


Paspalum lividum 0.5 1.3 0.3 0.6 2.2 2.4 0.5

Tab le C . 2 5 : C o n t i n u e d .

CATTLE

148

DEER

B r o w s e

S M C M S H C H S M C M S H C H

Schizachyrium scoparium 5.5 1.2 6.7 0,9 6.3 0.7 7.1 0.1



Celtis laevigata T T 4.5 1.4 6.2 3.1

Celtis pallida 2,7 0.3 0.1 4.8

Condalia hookeri 5,1 17.5 3.1 16.1

Diospyros texana T T 0.1 5.5 3.3 7.4 2.0

Eysenhardtia texana 1.7 5.4 0.3

Prosopis glandulosa 0.6 1.2 1.9 3.2 3.3 5.0 4.6 2.2

APPENDIX D

ANALYSIS OF VARIANCE TABLES OF FORAGING

BEHAVIOR OF TRACTABLE WHITE-TAILED DEER

149

150

p 0 0

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deer and cattle foraging strategies under different

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