RANGE SIZE AND HABITAT USE OF ELK IN THE GLASS MOUNTAINS, TEXAS
A Thesis
By
BRENDAN R. WITT
Submitted to the School of Agricultural and Natural Resource Sciences
Sul Ross State University, in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE
December 2008
Major Subject: Range and Wildlife Management
RANGE SIZE AND HABITAT USE OF ELK IN THE GLASS MOUNTAINS, TEXAS
A Thesis
By
BRENDAN R. WITT
Approved as to style and content by:
______Louis A. Harveson, Ph.D. Patricia Moody Harveson, Ph.D. (Chair of Committee) (Member)
______Bonnie J. Warnock, Ph.D. (Member)
______Robert J. Kinucan, Ph.D. Dean of Agricultural and Natural Resource Sciences
ABSTRACT
As recently as the end of the nineteenth century, Texas had a native population of
Merriam’s elk (Cervus elaphus merriami) living in the southern Guadalupe Mountains.
Since the extirpation of this subspecies ca. 1915, state agencies and landowners began re- introducing Rocky Mountain elk (C. e. nelsoni) into west Texas as early as 1928.
Currently, there are 5 mountain ranges in west Texas with free-ranging populations of elk, but very little information is available pertaining to their ecology and overall management. We initiated a study to better understand movements and habitat use of elk in the Glass Mountains of west Texas. We captured and radioed 14 elk (3 M, 11 F) in fall 2006 - spring 2007 using free range darting and net guns fired from helicopters.
Home range sizes (100% minimum convex polygon) averaged 345 ± 24 km² for males and 145 ± 63 km² for females using an average of 79 locations for each individual. Eight broad classes of habitats were delineated: riparian, tobosa (Hilaria mutica) grassland, juniper (Juniperus coahuilensis) woodland, mesquite (Prosopis glandulosa)-tarbush
(Flourensia cernua) scrubland, creosote (Larrea tridentata)-mariola (Parthenium incanum) scrubland, desert grassland, desert scrubland, and evergreen woodland. Elk selected for juniper woodland, riparian, and evergreen woodland habitats and avoided tobosa grassland, creosote-mariola scrubland, desert grassland, and desert scrubland habitats. Mesquite-tarbush was used in proportion to availability. Because annual ranges were so large in the privately owned matrix, it is essential that management be conducted on a landscape scale rather than property specific and be focused on juniper woodland, riparian, and evergreen woodland habitats.
iii
DEDICATION
I dedicate this thesis to my mother, Marika R. Will, and my grandfather, William
R. Ralston. Without my mothers support during my undergraduate career I might not be writing this thesis today. She helped through tough times and even when I wanted to give up she helped to push me along. She helped me get to where I am today and for that
I am overwhelmingly grateful. My grandfather helped me understand where I wanted to be and what I wanted to know even if he did not realize it. I will never forget when he would take me fishing on the Kentucky lakes around where I was born and help me to appreciate wildlife. I wish he was here so I could show him what I have accomplished in an area he loved so much. I miss you Opa, I wish to one day be as good of a man as you were.
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ACKNOWLEDGMENTS
I would like to thank my committee chair, Dr. Louis Harveson, and my committee members, Dr. Bonnie Warnock and Dr. Partricia Moody Harveson, for helping me through many obstacles throughout this project. I thank Sul Ross State University for support with many materials needed for the project. Thank you to Bobby Zoch, Homer
Mills, Chance Parker, Jim Daccus, Shad Shoenfelt, and Johnny Lanum for land access and all of your hard work throughout this project, without these land owners this project could not have happened. I thank Walt Eisenhour, Curtis Christianson, and the Rocky
Mountain Elk Foundation for believing in the Natural Resource Management program at
Sul Ross State University and for all of the monetary support throughout the entire project. Thank you to all Rocky Mountain Elk Foundation volunteers for helping tremendously with all captures. Thank you to all who helped to collect data in the field despite hot weather and the extreme west Texas wind. Thank you to my pilot, George
Vose, for flying with me twice a week and through tough weather and always getting us back safely. Thank you to my family for their complete support and understanding throughout my college career. I would also like to thank all my friends who helped me through tough times and thank you to my fiancé for all of her love and support throughout this project. Lastly, I would like to thank my grandfather, William R.
Ralston, for always taking the time to take me outside and show me what I truly wanted to know and understand - wildlife.
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TABLE OF CONTENTS
Page
ABSTRACT……………………………………………………………...... iii
DEDICATION...... iv
ACKNOWLEDGEMENTS………………………………………………...... v
TABLE OF CONTENTS…………………………………………………...... vi
LIST OF TABLES ………………………………………………………...... vii
LIST OF FIGURES ……………………………………………………...... viii
LIST OF APPENDICES……………………………………………………………… xi
INTRODUCTION…………………………………………….…………...... 1
CHAPTER I: IDENTIFYING ELK RANGE SIZE IN THE GLASS MOUNTAINS OF
TEXAS...... …...... …………… 5
CHAPTER II: USE OF HABITAT BY ELK IN THE GLASS MOUNTAINS,
TEXAS...... …...... 30
APPENDICES………………………………………………………………………... 56
VITA………………………………………………………………………...... 58
vi
LIST OF TABLES
Table Page
1.1 Annual, summer, and winter ranges as determined from radio telemetry locations for bull (M) and cow (F) elk in the Glass Mountains, Texas, November 2006 - March 2008…………………………………………... 25
2.1 Example of vegetation identification in the Glass Mountains using soil data for Brewster (TX622), Pecos (TX 371), and Jeff Davis (TX243) counties…………………………………………………………………... 36
2.2 Error matrix of the vegetation map derived from soils data in the Glass Mountains, Texas………………………………………………………… 38
2.3 Habitat characteristics of the study area for habitat use-availability analysis in the Glass Mountains, Texas, November 2006 – March 2008... 40
2.4 Annual selection ratios of bull (M) and cow (F) elk and percent use versus availability of the landscape in the Glass Mountains, Texas, November 2006 – March 2008…………………………………………... 41
2.5 Summer selection ratios of bull (M) and cow (F) elk and percent use versus availability of landscape in the Glass Mountains, Texas, November 2006 – March 2008…………………………………………... 43
2.6 Winter selection ratios of bull (M) and cow (F) elk and percent use versus availability of the landscape in the Glass Mountains, Texas, November 2006 – March 2008………………………………………………………. 45
vii
LIST OF FIGURES
Figure Page
1.1 Radiotelemetry locations and summer, winter, and annual home ranges (100% Minimum Convex Polygon) for elk M1 in the Glass Mountains, Brewster and Pecos counties, Texas, November 2006 - March 2008...... 11
1.2 Radiotelemetry locations and summer, winter, and annual home ranges (100% Minimum Convex Polygon) for elk M2 in the Glass Mountains, Brewster and Pecos counties, Texas, November 2006 - March 2008...... 12
1.3 Radiotelemetry locations and summer, winter, and annual home ranges (100% Minimum Convex Polygon) for elk M3 in the Glass Mountains, Brewster and Pecos counties, Texas, November 2006 - March 2008...... 13
1.4 Radiotelemetry locations and summer, winter, and annual home ranges (100% Minimum Convex Polygon) for elk F4 in the Glass Mountains, Brewster and Pecos counties, Texas, March 2007 - March 2008...... 14
1.5 Radiotelemetry locations and annual home range (100% Minimum Convex Polygon) for elk F5 in the Glass Mountains, Brewster and Pecos counties, Texas, March 2007 - March 2008. Summer and winter range sizes not calculated due to insufficient sample size...... 15
1.6 Radiotelemetry locations and summer, winter, and annual home ranges (100% Minimum Convex Polygon) for elk F6 in the Glass Mountains, Brewster and Pecos counties, Texas, March 2007 - March 2008...... 16
1.7 Radiotelemetry locations and summer, winter, and annual home ranges (100% Minimum Convex Polygon) for elk F7 in the Glass Mountains, Brewster and Pecos counties, Texas, March 2007 - March 2008...... 17
1.8 Radiotelemetry locations and summer, winter, and annual home ranges (100% Minimum Convex Polygon) for elk F8 in the Glass Mountains, Brewster and Pecos counties, Texas, March 2007 - March 2008...... 18
viii
Figure Page
1.9 Radiotelemetry locations and summer, winter, and annual home ranges (100% Minimum Convex Polygon) for elk F9 in the Glass Mountains, Brewster and Pecos counties, Texas, March 2007 - March 2008...... 19
1.10 Radiotelemetry locations and summer, winter, and annual home ranges (100% Minimum Convex Polygon) for elk F10 in the Glass Mountains, Brewster and Pecos counties, Texas, March 2007 - March 2008...... 20
1.11 Radiotelemetry locations and summer, winter, and annual home ranges (100% Minimum Convex Polygon) for elk F11 in the Glass Mountains, Brewster and Pecos counties, Texas, March 2007 - March 2008...... 21
1.12 Radiotelemetry locations and summer, winter, and annual home ranges (100% Minimum Convex Polygon) for elk F12 in the Glass Mountains, Brewster and Pecos counties, Texas, March 2007 - March 2008...... 22
1.13 Radiotelemetry locations and annual home range (100% Minimum Convex Polygon) for elk F13 in the Glass Mountains, Brewster and Pecos counties, Texas, March 2007 - March 2008. Summer and winter range sizes not calculated due to insufficient sample size...... 23
1.14 Radiotelemetry locations and summer, winter, and annual home ranges (100% Minimum Convex Polygon) for elk F14 in the Glass Mountains, Brewster and Pecos counties, Texas, March 2007 - March 2008...... 24
2.1 Locations of vegetation transects and ground truthing locations on study area overlaid onto a preliminary vegetation map derived from optimal forage conditions (map legend is located in Appendix C)……. 35
2.2 Annual habitat use-availability for bull and cow (A), bull (B), and cow (C) elk based on S ([U + 0.001]/[A + 0.001]) values in the Glass Mountains, Texas, November 2006 – March 2008……………………. 42
2.3 Summer habitat use-availability for bull and cow (A), bull (B), and cow (C) elk based on S ([U + 0.001]/[A + 0.001]) values in the Glass Mountains, Texas, November 2006 – March 2008……………….…….. 44
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Figure Page
2.4 Winter habitat use-availability for bull and cow (A), bull (B), and cow (C) elk based on S ([U + 0.001]/[A + 0.001]) values in the Glass Mountains, Texas, November 2006 – March 2008……………………. 46
x
LIST OF APPENDICES
Appendix Page
A Morphological measurements from elk captured in the Glass Mountains, Brewster and Pecos counties, Texas, October 2006 - March 2007...... 56
B Corrected vegetation map following ground truthing and DOQQ In comparison………...... Pocket
C Map legend used for figure 2.1 on page 35…………………………. 57
xi 1
INTRODUCTION
Elk (Cervus elaphus), one of the largest members of the Cervidae family, are
found throughout the western United States as well as in small, isolated populations in
central and eastern United States and Canada (Thomas and Toweill 1982). Significant
research has been conducted on these populations concerning several key ecological
features. The Rocky Mountains and Pacific Northwest account for the majority of the
research because the elk populations are well established and classified as game species.
Research on these populations include dynamics, reproduction, mortality, and habitat selection (Ward and Marcum, 2005; Beck et al., 2006; Wright et al., 2006; Christianson
and Creel, 2007; Eberhardt et al., 2007; Gagnon et al., 2007).
One of the areas of North America that is commonly overlooked, regarding elk, is
Texas. As recently as the end of the nineteenth century, Texas still had a native
population of Merriams’s elk (C. e. merriami) living in the southern Guadalupe
Mountains (Davis and Schmidly, 1994). However, excessive hunting and overgrazing by
livestock led to the extirpation of this subspecies shortly after the start of the twentieth
century (Thomas and Toweill, 1982). Since then, state agencies and landowners have
reintroduced Rocky Mountain elk (C. e. nelsoni) into west Texas.
Restoration efforts began in 1928 when Judge J. C. Hunter released 44 elk from
the Black Hills of South Dakota into the Guadalupe Mountains. This population rose to
approximately 400 individuals by 1938, but dwindled to a population of 40 in 1994
(Davis and Schmidly, 1994). Texas Parks and Wildlife released 48 Rocky Mountain elk
into the Davis Mountains and 51 Rocky Mountain elk into the Wylie Mountains in 1988.
These populations were thought to consist of 15-40 individuals per mountain range in
This thesis follows the style for the Southwestern Naturalist 2
1990 (Coykendall, 1990). In the early 1970’s, the Eagle Mountains received 25 elk
(Swepston, 1985) and were known to have between 15-40 individuals in 1994 (Davis and
Schmidly, 1994). The Glass Mountains also received elk in the mid-1940s by Ira “Cap”
Yates (Grace, 1983). Yates initially released 1 bull and 2 cows to the area, and in 1994
the population was thought to have 150-180 individuals (Davis and Schmidly, 1994).
Although there are historical accounts of elk introductions in west Texas, it is believed
that many undocumented releases have occurred in this region.
In 1959, elk were added to the game species list in Texas (Davis and Schmidly,
1994), but due to the fact that the present species is non-native, elk were relisted as
“exotic livestock” in 1997 by the 76th legislature. Davis and Schmidly (1994) report that
elk occurred in 5 mountain ranges in the Trans-Pecos including the Guadalupe, Glass,
Eagle, Wylie, and Davis mountains. The Glass Mountains are thought to have one of the
largest populations in the Trans-Pecos. Although populations have been established
throughout west Texas, there is limited information concerning habitat use, movements,
home range, and overall ecology. Ecological data of free ranging elk populations is
essential if they are to be managed in the west Texas region.
The goal of this study was to gather objective data on the ecology of elk that will
aid in making management plans in the Trans-Pecos region of Texas. Specifically, my
objectives were to: 1) estimate elk annual and seasonal home range size, 2) gain a better
understanding of how elk should be managed at the landscape scale within privately
owned land 3) create an accurate vegetation map of the Glass Mountains using soil data,
and 4) determine habitat selection of elk in the Glass Mountains. Objectives 1 and 2 are
addressed in chapter 1 and objectives 3 and 4 are addressed in chapter 2 of this thesis.
3
LITERATURE CITED
BECK, J.L., J. M. PEEK, AND E. K. STRAND. 2006. Estimates of elk summer range
nutritional carrying capacity constrained by probabilities of habitat selection.
Journal of Wildlife Management 70:283-294.
CHRISTIANSON, D. A., AND S. CREEL. 2007. A review of environmental factors affecting
elk winter diets. Journal of Wildlife Management 71:164-176.
COYKENDALL, A. 1990. 1988 elk transplants in the Davis Mountains, Jeff Davis County,
and the Wylie Mountains, Culberson County, Texas. Thesis, Sul Ross State
University, Alpine, Texas, USA.
DAVIS, W. B., AND D. J. SCHMIDLY. 1994. The mammals of Texas. University of Texas
Press, Austin, Texas, USA.
EBERHARDT, L.L., P. J. WHITE, R. A. GARROTT, AND D. B. HOUSTON. 2007. A seventy-
year history of trends in Yellowstone’s northern elk herd. Journal of Wildlife
Management 71:594-602.
GAGNON, J. W., T. C. THEIMER, N. L. DODD, S. BOE, AND R. E. SCHWEINSBURG. 2007.
Traffic volume alters elk distribution and highway crossings in Arizona. Journal
of Wildlife Management 71:1344-1348.
GRACE, K. T. 1983. A preliminary ecological study of elk in the Glass Mountains,
Brewster County, Texas. Thesis, Sul Ross State University, Alpine, Texas, USA.
SWEPSTON, D. A. 1985. Big game investigation-elk introductions. Texas Parks and
Wildlife Department, Federal Aid in Wildlife Restoration, Progress Report,
Project W-109-R-7, Job 52. 49p.
4
THOMAS, J. W., AND D. E. TOWEILL. 1982. Elk of North America: ecology and
management. Stackpole Books, Harrisburg, Pennsylvania, USA.
WARD, R.L., AND C. L. MARCUM. 2005. Lichen litterfall consumption by wintering deer
and elk in western Montana. Journal of Wildlife Management 69:1081-1089.
WRIGHT, G.J., R. O. PETERSON, D. W. SMITH, AND T. O. LEMKE. 2006. Selection of
northern Yellowstone elk by gray wolves and hunters. Journal of Wildlife
Management 70:1070-1078.
5
CHAPTER I:
IDENTIFYING ELK RANGE SIZE IN THE GLASS MOUNTAINS OF TEXAS
Home range estimates for North American elk have been well documented
(Waldrip and Shaw, 1979; Jenkins and Starkey, 1982, 1991; Irwin and Peek, 1983;
McCorquodale et al., 1989), but most of these estimates have concerned mesic montane or coastal forests (McCorquodale et al., 1989) in the Pacific Northwest or Rocky
Mountain regions. Little data is available pertaining to elk in arid to semi-arid environments throughout the United States. An arid shrub-steppe environment in
Washington showed home ranges of 161.4 km² (McCorquodale et al., 1989) while an arid environment in Idaho documented home range sizes of 480 km² (Strohmeyer and Peek,
1996). With such a large difference in ranges between these two environments, it is important to understand the various regions that elk inhabit and what factors lead to these diverse ranges.
The Trans-Pecos region of west Texas is an environment that is commonly overlooked regarding elk. Texas had a native population of Merriams’s elk (C. e. merriami) in the southern Guadalupe Mountains (Davis and Schmidly, 1994) as recently as the end of the nineteenth century. Due to excessive hunting and overgrazing by livestock, this species was extirpated shortly after the start of the twentieth century
(Thomas and Toweill, 1982).
Krysl (1979), Moody (1979), Grace (1983), and Coykendall (1990) have all conducted research that is extremely valuable, but they lack data and sample sizes that
6
are needed to truly understand the elk populations in west Texas. Of all the research that has been conducted in Texas, only Moody (1979) and Coykendall (1990) were related to home range and dispersal with the use of telemetry. Krysl (1979) studied food habits and vegetative impacts of elk in the Guadalupe Mountains but did not address habitat preference. Moody (1979) also conducted his research in the Guadalupe Mountains and found that the population consisted of 120-130 elk in 1978 and covered an area of 139
km2 using telemetry and visual observations. During 1982-1983, a general ecology study
on the Glass Mountain herd took place and estimated the size of the population to be between 161-168 elk (Grace, 1983). Grace (1983) used King’s strip census, Kelker’s strip census, and a pellet group count to estimate the population size. Grace (1983) found that oak (Quercus sp.) woodlands and riparian areas were the preferred habitat types but based his findings on visual observation rather than radio telemetry. It is believed they were preferred due to the increased cover and high abundance of forage. Grace (1983) also found that the herd had a low natality rate and low sub-adult to adult ratio implicating predation by mountain lions (Puma concolor), coyotes (Canis latrans), and bobcats (Lynx rufus). Coykendall (1990) conducted research to monitor the health and dispersal of released elk. Coykendall (1990) radio-collared 5 cows in the Davis
Mountains and 4 cows in the Wylie Mountains and found that only 6 of the 9 individuals remained after 6 months of monitoring. The majority of the collared animals traveled
<10 km from the release site and mortality was estimated to be 13%, with most deaths being attributed to mountain lion predation and motor vehicle accidents.
Because of the lack of biological data on overall movements of elk in this arid environment, I sought to gain a better understanding of elk annual and seasonal ranges
7
with the aid of VHF collars and GIS analysis. My specific objectives were to 1) estimate
the annual and seasonal home range, and 2) gain a better understanding of how elk should
be managed at the landscape scale within privately owned land.
METHOD--Study area--The Glass Mountains are a partially isolated range, located
in the northeastern part of Brewster County and extend as low interrupted hills well into
Pecos County southwest of Ft. Stockton (Warnock, 1977). They cover 780 km2 of the
northeastern Chihuahuan Desert (Grace, 1983). The thrust of the range extends 48 to 64
km from Altuda in a northeasterly direction and has an average width of about 16 to 32
km (Warnock, 1977). Topography ranges from rolling hills in the northeastern regions to
tall, steep mountains in the southern region with elevations ranging from 1,200 to 2,100
m. This mountain range received its name from the Spanish translation of “Sierra del
Vidrio” given to the mountains due to the glassy appearance of the limestone scarps
(Grace, 1983). The vegetation in the Glass Mountains is quite diverse with species
including catclaw acacia (Mimosa biuncifera), beargrass (Nolina texana), sotol
(Dasylirion leiophyllum), grey oak (Quercus grisea), junipers (Juniperus sp.), and pinyon pine (Pinus cembroides). Rainfall typically occurs in mid and late summer and is on average very low (Grace, 1983). The general climate of the entire Trans-Pecos can be characterized by arid to semi-arid with dry winters and hot, dry summers. The average precipitation is around 355.6 mm, with the Glass Mountains residing in the more humid
portion of the province (O’Toole, 2005). Most geologic formations are primarily
limestone in composition and include the Wolfcamp, Hess, Leonard, Word, Capitan, and
Bissett formations (Warnock, 1977). Trespass privileges were granted by numerous
8
privately owned ranches within the Glass Mountains. Initial work began on a ranch
located near Mills Road off highway 67, northeast of Alpine.
Data collection and analysis--Two capture methods were used throughout the study period. The initial capture included darting elk from blinds and immobilizing them with 600 mg xylazine plus 200 mg telezol as adapted from Kreeger (1996). Elk were provided an antagonist of 1,000 mg tolazoline. The second capture method incorporated a net gun fired from a Bell helicopter and was used to capture elk on 3 primary ranches located within the Glass Mountains. Elk were collared using necklace type transmitters
(Model LMRT-4 Lotek Wireless Incorporated Newmarket, Ontario, Canada).
Upon capture, elk were hobbled, blind folded, fitted with radio collars, palpated to determine reproductive status if necessary, and also aged according to tooth replacement and wear (Heffelfinger, 1997). A veterinarian inspected all elk, monitored stress levels, and took blood samples. Collared elk were identified by number and by M or F, indicating the gender of each animal. General information on capture date, gender, age, location, method, morphology, and overall condition was recorded for captured elk.
For this portion of the study, aerial and ground telemetry was conducted from 11
November 2006 to 20 March 2008. A Cessna-172 fixed wing aircraft was used for aerial monitoring with 2 antennas (Model RA-2AK, Telonics, Mesa, Arizona) mounted to the wing struts. A receiver (Model TR-2) and directional control unit (Model TAC-2-RLB) were used by observers in the cockpit. Ground locations were taken on availability using standard triangulation procedures outlined by White and Garrott (1990) with the aid of a receiver and a 3-element folding yagi antenna (ATS, Isanti, Minnesota). All ground telemetry locations were calculated by Location of a Signal™ (LOAS; version 3.0.3).
9
Due to the mobility of the elk coupled with limited private land access, aerial telemetry was the dominant method for locating elk.
All locations were manually imported into ArcGIS® 9.2 (ESRI, Redlands,
California, USA). Hawth’s Analysis tools extension was downloaded into ArcGIS®
(Version 3.26, 2006) and was used to determine the annual 100% minimum convex
polygon of all elk (Beyer, 2004). The X Tools Pro extension (Version 5.1) for ArcGIS® was then used to calculate the area of individual annual ranges. Seasonal ranges were
calculated in the same manner but using the following descriptions: winter (Sep-Mar) and
summer (Apr-Aug). Annual and seasonal movements were determined by taking 2 aerial
locations per week for approximately 17 months (Nov 2006 - Mar 2008).
RESULTS--Capture-- During the course of the study, capture activities in the Glass
Mountains were conducted in October 2006 and March 2007. Fourteen elk (3 M, 11 F) were trapped via free range darting and net guns discharged from a helicopter. All bulls were captured via free range darting and all cows were capture with the use of net guns shot from helicopters. Helicopter capture required the use of many volunteers but aided in a quick release and excluded non-target species.
Radiotelemetry--A total of 947 locations was recorded throughout the study period for all individuals consisting of 500 locations for summer and 447 locations for winter. Cows accounted for 71.1% of radio locations. Most locations were recorded between 0900 and 1200 hours. Mortalities were recorded when found using aerial telemetry. During this phase of the study, only 2 mortalities were recorded. Because home ranges were so large and aerial locations were taken twice a week, mortalities were found 3-4 days post mortem. Subsequently, the exact cause of death was difficult to
10
determine. No elk died as a result of capture myopathy (≤15 days post capture). Mean
radio location error was 0.97 km (SD = 0.68) and ranged from 0.27-2.52 km.
Annual, winter, and summer range sizes were recorded for all elk (Fig 1.1 – 1.14).
A mean of 79 locations per individual was used to determine annual range size. Mean
annual range size for bulls (345 ± 237 km²) was larger (P = 0.036) than for cows (145 ±
63.05 km²); (Table 1.1). Winter range size was calculated using a mean of 33 locations
per individual while summer range size was calculated using a mean of 42 locations per
individual. Mean summer range size for bull elk (172 ± 76 km²) was larger (P = 0.209) than for cows (102.33 ± 46km²). Winter range size for bulls (277 ± 226 km²) was also larger (P = 0.036) than for cows (100 ± 64 km²). I excluded the 2 mortalities during the study as sample size was inadequate.
DISCUSSION-- Elk home range, seasonal range, and migratory patterns have been well documented throughout the United States (McCorquodale et al., 1989;
McCorquodale, 2003; Christianson and Creel, 2005; Beck et al., 2006) but most research has been located within forested lands. McCorquodale et al. (1989) is one of the few that have conducted elk research in an arid environment and found that cow elk in
Washington had an annual range size of 161.4 ± 8.5 km² and bull elk had an annual range size of 163.1 ± 17.4 km². His data is similar in regard to cows in the Glass Mountains, but contrary of what has been found for bulls. Annual range size for bulls in the Glass
Mountains was almost double that found by McCorquodale et al. (1989). McCorquodale
et al. (1989) also noted that the annual range in Washington was 3-10 times larger than
for research conducted on areas dominated by highly forested land (Jenkins and Starkey,
1982; Irwin and Peek, 1983; Edge et al., 1985).
11
FIG. 1.1--Radiotelemetry locations and summer, winter, and annual home ranges
(100% Minimum Convex Polygon) for elk M1 in the Glass Mountains, Brewster and
Pecos counties, Texas, November 2006 - March 2008.
12
FIG. 1.2--Radiotelemetry locations and summer, winter, and annual home ranges
(100% Minimum Convex Polygon) for elk M2 in the Glass Mountains, Brewster and
Pecos counties, Texas, November 2006 - March 2008.
13
FIG. 1.3--Radiotelemetry locations and summer, winter, and annual home ranges
(100% Minimum Convex Polygon) for elk M3 in the Glass Mountains, Brewster and
Pecos counties, Texas, November 2006 - March 2008.
14
FIG. 1.4--Radiotelemetry locations and summer, winter, and annual home ranges
(100% Minimum Convex Polygon) for elk F4 in the Glass Mountains, Brewster and
Pecos counties, Texas, March 2007 - March 2008.
15
FIG. 1.5--Radiotelemetry locations and annual home ranges (100% Minimum
Convex Polygon) for elk F5 in the Glass Mountains, Brewster and Pecos counties, Texas,
March 2007 - March 2008. Summer and winter range sizes not calculated due to insufficient sample size.
16
FIG. 1.6--Radiotelemetry locations and summer, winter, and annual home ranges
(100% Minimum Convex Polygon) for elk F6 in the Glass Mountains, Brewster and
Pecos counties, Texas, March 2007 - March 2008.
17
FIG. 1.7--Radiotelemetry locations and summer, winter, and annual home ranges
(100% Minimum Convex Polygon) for elk F7 in the Glass Mountains, Brewster and
Pecos counties, Texas, March 2007 - March 2008.
18
FIG. 1.8--Radiotelemetry locations and summer, winter, and annual home ranges
(100% Minimum Convex Polygon) for elk F8 in the Glass Mountains, Brewster and
Pecos counties, Texas, March 2007 - March 2008.
19
FIG. 1.9--Radiotelemetry locations and summer, winter, and annual home ranges
(100% Minimum Convex Polygon) for elk F9 in the Glass Mountains, Brewster and
Pecos counties, Texas, March 2007 - March 2008.
20
FIG. 1.10--Radiotelemetry locations and summer, winter, and annual home ranges
(100% Minimum Convex Polygon) for elk F10 in the Glass Mountains, Brewster and
Pecos counties, Texas, March 2007 - March 2008.
21
FIG. 1.11--Radiotelemetry locations and summer, winter, and annual home ranges
(100% Minimum Convex Polygon) for elk F11 in the Glass Mountains, Brewster and
Pecos counties, Texas, March 2007 - March 2008.
22
FIG. 1.12--Radiotelemetry locations and summer, winter, and annual home ranges
(100% Minimum Convex Polygon) for elk F12 in the Glass Mountains, Brewster and
Pecos counties, Texas, March 2007 - March 2008.
23
FIG. 1.13--Radiotelemetry locations and annual home range (100% Minimum
Convex Polygon) for elk F13 in the Glass Mountains, Brewster and Pecos counties,
Texas, March 2007 - March 2008. Summer and winter range sizes not calculated due to insufficient sample size.
24
FIG. 1.14--Radiotelemetry locations and summer, winter, and annual home ranges
(100% Minimum Convex Polygon) for elk F14 in the Glass Mountains, Brewster and
Pecos counties, Texas, March 2007 - March 2008.
25
TABLE 1.1--Annual, summer, and winter ranges as determined from radio
telemetry locations for bull (M) and cow (F) elk in the Glass Mountains, Texas,
November 2006 - March 2008.
Annual range Summer range Winter range
Elk # n Size (km²) n Size (km²) n Size (km²)
M1 90 221 41 132 49 154
M2 91 619 38 260 53 538
M3 93 196 42 126 51 140
X¯ 91 345 ± 237 40 172 ± 76 51 277 ± 226
F4 76 102 43 53 33 51
F5 3 ª 3 ª - ª
F6 76 140 43 104 33 114
F7 76 132 42 133 34 41
F8 77 288 42 155 35 249
F9 74 132 42 90 32 94
F10 75 187 41 185 34 120
F11 75 90 43 62 32 75
F12 74 156 42 79 32 111
F13 11 ª 11 ª - ª
F14 70 80 41 61 29 45
X¯ 75 145 ± 63 42 102 ± 46 33 100 ± 64
ª Insufficient number of locations to determine range size; caused mortality unknown
26
Strohmeyer and Peek (1996) found winter ranges in Idaho to cover 438-480 km² and summer ranges covered 114-220 km². Winter and summer ranges in the Glass
Mountains were much less than what was found in Idaho. Seasonal migration may be a factor between these two home range estimates. The Glass Mountains do not have a drastic change between the seasons so elk in this area may not have to travel to find adequate forage between the seasons. Idaho has large amounts of snowfall in winter and may cause elk to travel further from one area to another in order to find nutrients that are not located beneath snow cover.
Jewell (1966) suggests that an animal’s home range size is related to population density, habitat quality, and energy requirements of the animal. The latest population estimate for the Glass Mountains was 150-180 individuals (Davis and Schmidly, 1994).
The annual range from my study may indicate the elk population is at or near the carrying capacity and elk must travel further to acquire needed nutrition. Home range size within a species typically increases with decreasing food density (McNab, 1963). The arid environment of the study site may not have the nutritional quality and quantity needed to support a large number of animals. Another factor in this area that may lead to larger than average annual range size may be limited free standing water. Private landowners have water troughs located throughout their land to aid with cattle operations and elk also utilize these water sources. The combination of a high population density, low forage production, and the possible lack of free water may be contributors to such large annual ranges.
MANAGEMENT IMPLICATIONS--Because bull and cow elk had relatively large home ranges in the Glass Mountains, it is imperative that this population be managed on
27 a landscape scale rather than property specific. Since this species does not have a regulated hunting season in Texas, landowners should work together to create their management plans and harvest limits. Population estimates are needed to assist landowners in setting harvest limits. Initial management plans should focus on the limiting factors in the Glass Mountains. These factors may include the availability of water and adequate forage. An assessment of water availability and forage production
(carrying capacity estimates) is warranted if landowners in the Glass Mountains value the elk resource.
LITERATURE CITED
BECK, J. L., J. M. PEEK, AND E. K. STRAND. 2006. Estimates of elk summer range
nutritional carrying capacity constrained by probabilities of habitat selection.
Journal of Wildlife Management 70:283-294.
BEYER, H. L. 2004. Hawth's Analysis Tools for ArcGIS. Available at
http://www.spatialecology.com/htools. (Accessed January 2007)
COYKENDALL, A. 1990. 1988 elk transplants in the Davis Mountains, Jeff Davis County,
and the Wylie Mountains, Culberson County, Texas. Thesis, Sul Ross State
University, Alpine, Texas, USA.
CHRISTIANSON, D. A., AND S. CREEL. 2005. A review of environmental factors
affecting elk winter diets. Journal of Wildlife Management 71:164-176.
DAVIS, W. B., AND D. J. SCHMIDLY. 1994. The mammals of Texas. University of Texas
Press, Austin, Texas, USA.
28
EDGE, W. D., C. L. MARCUM, AND S. L. OLSON. 1985. Effects of logging activities on
home range fidelity of elk. Journal of Wildlife Management 49:741-744.
GRACE, K. T. 1983. A preliminary ecological study of elk in the Glass Mountains,
Brewster County, Texas. Thesis, Sul Ross State University, Alpine, Texas, USA.
HEFFELFINGER, J. 1997. Age criteria for Arizona game species. Arizona Game and Fish
Department Special Report 19. Tucson, Arizona, USA.
IRWIN, L. L., AND J. M. PEEK. 1983. Elk habitat use relative to forest succession in Idaho.
Journal of Wildlife Management 47:664-672.
JENKINS, K. J., AND E. E. STARKEY. 1982. Social organization of Roosevelt elk in an old-
growth forest. Journal of Mammalogy 63:331-334.
JEWELL, P. A. 1966. The concept of home range in mammals. Symposium Zoological
society of London 18:85-109.
KREEGER, T. J. 1996. Handbook of wildlife chemical immobilization. International
Wildlife Veterinary Services, Laramie, Wyoming, USA.
KRYSL, L. J. 1979. Food habits of mule deer and elk, and their impact on vegetation in
Guadalupe Mountains National Park. Thesis, Texas Tech University, Lubbock,
Texas, USA.
MCCORQUODALE, S. M. 2003. Sex-specific movements and habitat use by elk in the
Cascade Range of Washington. Journal of Wildlife Management 67:729-741.
MCCORQUODALE, S. M., RAEDEKE, K. J.,AND TABER, R. D. 1989. Home ranges of elk in
an arid environment. Northwest Science 63:29-34.
MCNAB, B. K. 1963. Bioenergetics and the determination of home range size.
American Naturalist 97:133-140.
29
MOODY, J. D. 1979. Ecology and population dynamics of elk in Guadalupe Mountains
National Park, Texas. Thesis, Texas Tech University, Lubbock, Texas, USA.
O’TOOLE, M. D. 2005. A comparative vegetation study of the Cook Ranch fire, Brewster
and Pecos counties, Texas. Thesis, Sul Ross State University, Alpine, Texas,
USA.
STROHMEYER, D. C., AND J. M. PEEK. 1996. Wapiti home range and movement patterns in
a sagebrush desert. Northwest Science 70:79-87.
THOMAS, J. W., AND D. E. TOWEILL. 1982. Elk of North America: ecology and
management. Stackpole Books, Harrisburg, Pennsylvania, USA.
WALDRIP, G. P., AND J. H. SHAW. 1979. Movements and habitat use by cow and calf elk
in the Wichita Mountains National Wildlife Refuge. In: M. S. Boyce and L. D.
Hayden-Wind, editors. North American elk: ecology, behavior and management.
Stackpole Books, Harrisburg, Pennsylvania, USA. Pp. 177-184.
WARNOCK, B. H. 1977. Wildflowers of the Davis Mountains and the Marathon Basin,
Texas. Sul Ross State University, Alpine, Texas, USA.
WHITE, G. C. AND R. A. GARROTT. 1990. Analysis of wildlife radio-tracking data.
Academic Press, San Diego, California, USA.
30
CHAPTER II:
USE OF HABITAT BY ELK IN THE GLASS MOUNTAINS, TEXAS
Elk (Cervus elaphus) prefer areas of edge habitat (Thomas et al., 1979; Irwin and
Peek, 1983) where the quality of forage and forest cover are in close proximity (Sawyer
et al., 2007). Elk, and other ungulate habitat use, is regulated by the need to minimize
predation risk and thermal stress while still maximizing net energy intake (Wiens, 1976;
Fryxell and Lundberg, 1997; Aycrigg and Porter, 1997; Anderson et al., 2005). Net energy intake is fulfilled by habitats that hold the most nutrient rich forage. Nutritional quality and quantity of forage can have an influence on a species ability to reproduce and can also manage how many individuals are virulent enough to successfully breed
(Toweill and Thomas, 2002). Nutrition plays a fundamental role in determining carrying capacity, home range size, and which habitats offer the nutritional requirements for basic life processes (Toweill and Thomas, 2002).
Of all the ungulates in North America, Rocky Mountain elk (C. e. nelsoni) are one of the most widely distributed and studied species (Sawyer et al., 2007), but most research concerning elk habitat use has been based on montane or forested environments
(Larkin et al., 2003; Anderson et al., 2005; Mao et al., 2005; Beck et al., 2006; Dyke and
Darragh, 2007). Although this data is extremely valuable, wildlife managers also need to understand how this species interacts within other habitats. Very few studies have focused on habitat use by elk in arid to semi-arid environments (McCorquodale et al.,
1989; McCorquodale, 1991; Strohmeyer and Peek, 1996). With recent range expansions, elk have shown their ability to adapt to many types of areas and habitats (Lindzey et al.,
31
1997). Craighead et al. (1973) and Geist (1978) have also stated that elk have the
capability to learn and adjust to favorable and unfavorable conditions; this may lead to
different habitat preferences within different environments.
Few studies have addressed habitat use and preference in west Texas (Krysl,
1979; Grace, 1983). Krysl (1979) conducted his research in the Guadalupe Mountains
and studied food habits and elk impacts on vegetation but did not address habitat
preference. In that study, the elk diet was comprised of 32% grass, 20% forbs, and 48%
browse (Krysl, 1979). Although understanding their diet is extremely beneficial
concerning how to manage this species, a further understanding of elk habitat use is
needed. Grace (1983) attempted to address habitat use by elk in the Glass Mountains.
Based on visual observations rather than radio telemetry, he concluded that oak (Quercus
sp.) woodlands and riparian areas were the preferred habitat types because they had
increased cover and high abundance of various foods.
With an inadequate understanding of how elk utilize habitats in arid to semi-arid
environments, I sought to evaluate elk habitat use and preference in the Glass Mountains.
Specific objectives were to: 1) create an accurate vegetation map of the Glass Mountains
using soil data, and 2) determine habitat selection of elk in the Glass Mountains.
METHODS--Study Area—The Glass Mountains are located approximately 30 km
east of Alpine, Texas and cover 780 km2 of the Northeast Chihuahuan Desert (Grace,
1983). This isolated range is located in the northeastern part of Brewster County and extend as low interrupted hills southwest of Ft. Stockton in Pecos County (Warnock,
1977). Topography ranges in elevation from 1,200 to 2,100 m and is predominantly limestone in composition. Geologic formations include the Hess, Word, Wolfcamp,
32
Leonard, Bissett, and Capitan (Warnock, 1977). This range received its name from the
translation of the Spanish term “Sierra del Vidrio” which was given because of the glassy
appearance of the limestone scarps (Grace, 1983).
Average precipitation of the Trans-Pecos is 355.6 mm, with the Glass Mountains
located in the more humid portion of the region (O’Toole, 2005). Rainfall in the Glass
Mountains usually occurs in mid to late summer and is on average very low (Grace,
1983). The general climate of the entire Trans-Pecos is considered to be arid to semi-arid
with dry winters and hot, dry summers. Vegetation in the area includes beargrass (Nolina
texana), sotol (Dasylirion leiophyllum), lechuguilla (Agave lechuguilla), grey oak
(Quercus grisea), red berry juniper (Juniperus pinchotii), pinyon pine (Pinus
cembroides), and catclaw acacia (Mimosa biuncifera). Numerous core ranches within the
Glass Mountains granted trespass privileges. Initial work began northeast of Alpine on a
ranch located near Mills Road off highway 67.
Capture and monitoring--Elk were captured by darting from blinds and the use of
net guns fired from helicopters. Eleven elk were immobilized with 600 mg xylazine plus
200 mg telezol as adapted from Kreeger (1996). The remaining elk were captured using a
net gun fired from a Bell helicopter. Elk were collared using necklace type transmitters.
Upon capture, elk were restrained, measured, radioed, and released.
I monitored elk using aerial and ground radiotelemetry from 11 November 2006
to 20 March 2008. Most locations were obtained from a Cessna-172 fixed wing aircraft
with 2 H-antennas mounted to the wing struts. Ground locations were taken upon
availability using standard triangulation procedures (White and Garrott, 1990) using a
receiver and a 3-element folding yagi antenna. Location of a Signal™ (LOAS; version
33
3.0.3) was used to calculate all ground telemetry locations. Due to limited private land access coupled with the mobility of the elk, the dominant method for locating individuals was aerial telemetry.
Habitat delineation--A general reconnaissance was conducted on the study site and 8 habitat communities were visually found. These habitat communities included riparian, tobosa (Hilaria mutica) grassland, juniper (Juniperus pinchotii) woodland, mesquite (Prosopis glandulosa)-tarbush (Flourensia cernua) scrubland, creosote (Larrea tridentata)-mariola (Parthenium incanum) scrubland, desert grassland, desert scrubland, and evergreen woodland. Once habitat communities were found, a stratified random sampling technique was used to determine structure and composition. Eighty transects were conducted with 10 being placed in each habitat community. The three methods used for vegetation sampling included line intercept, quadrat, and height pole. Line intercept and quadrat methods (Canfield, 1941) were used to measure abundance and canopy coverage while the height pole was used to sample lateral visibility (Guthery et al., 1981). Transects were conducted with the aid of 30-m fiberglass tape, Daubenmire quadrat (20 x 50 cm), and 1-m height pole.
Digital Orthophoto Quarter-Quadrangles (DOQQ) of the designated study area were downloaded from the Texas Natural Resource Information System (TNRIS, 2006) and added to ArcGIS® 9.2 (ESRI, Redlands, California, USA). For greater visual analysis, all DOQQs were uploaded into ERDAS Imagine® 9.0 (Leica Geosystems,
Norcross, Georgia) to create a color corrected mosaic. This mosaic was then uploaded into ArcGIS®.
34
Soils data were then downloaded from the Natural Resources Conservation
Service (NRCS) database for Pecos, Brewster, and Jeff Davis. All counties utilized an
individual county description for all soils. To better understand the soils in all 3 counties
I used the national soil key found within the metadata of those counties. The national soil
key offered soil and soil complex classification. Soil complexes incorporated multiple
soil series. I chose the soil series which incorporated the highest percentage within the
complex. County soil maps were clipped to the DOQQ mosaic of the study site.
Once the soil data was clipped to the size of the DOQQ mosaic, transect locations
were overlaid and underlying soil polygons were recorded for individual vegetation classes. If a transect location had a higher percentage in a certain soil, that soil was classified as the vegetation type of that transect. Many soil polygons within the map did not contain transect data, meaning there were no transect locations that fell within those soils. For these soils the Range Site Description (RSD) was downloaded from NRCS and organized by the optimal forage conditions. The optimal forage condition allowed the organization of soils into the pre-determined vegetation classes. The soils were re- classified by polygon to the optimal forage condition for that soil. The optimal forage condition can be considered to be the climax vegetation type for the soil.
Three main highways surrounding the study area aided in analysis. Highway 67, highway 90, and highway 385 were driven for ground truthing purposes. These highways offered the opportunity to visually document and record vegetation changes throughout the landscape. Fifty-six pictures and locations were overlaid onto the optimal forage condition vegetation map data (Fig. 2.1). Underlying polygons were then reclassified to show the true vegetation located within those areas (Table 2.1).
FIG. 2.1--Locations of vegetation transects and ground truthing locations on study area overlaid onto a preliminary vegetation map derived from optimal forage conditions (map legend can be found in Appendix C).
35
TABLE 2.1--Example of vegetation identification in the Glass Mountains using soil data for Brewster (TX622), Pecos (TX
371), and Jeff Davis (TX243) counties.
County I.D. County description National I.D. RSDd Opitimal Forage Condition Corrected
TX243 BeBa 58461 Shallow (Mixed Prairie) Juniper Woodland Juniper Woodland
TX243 BeBa 58461 Shallow (Mixed Prairie) Juniper Woodland Juniper Woodland
TX243 BeBa 58461 Shallow (Mixed Prairie) Juniper Woodland Juniper Woodland
TX371 10b 58499 Shallow Divide PE 19-25 Juniper Woodland Evergreen Woodland
TX371 10b 58499 Shallow Divide PE 19-25 Juniper Woodland Evergreen Woodland
TX371 10b 58499 Shallow Divide PE 19-25 Juniper Woodland Juniper Woodland
TX622 BOBc 58830 Shallow (Mixed Prairie) Juniper Woodland Desert Grassland
TX622 BOBc 58830 Shallow (Mixed Prairie) Juniper Woodland Desert Grassland
TX622 BOBc 58830 Shallow (Mixed Prairie) Juniper Woodland Juniper Woodland a Boracho-Espy association, gently sloping b Ector-Upton association, gently undulating c Boracho-Espy complex, gently undulating d Range site description 36
37
I used a random numbers generator in ArcGIS® using Hawth’s tools (Version
3.26, 2006) to place 100 random points onto the DOQQ mosaic (Beyer, 2004). Once a vegetation community for an individual point was identified in the DOQQ, the vegetation map was overlaid onto the mosaic. The point that was determined from the DOQQ was then compared to the corrected vegetation map to find the accuracy (Table 2.2).
Use-availability analysis-- All locations were added to Microsoft Excel® spreadsheets and manually imported into ArcGIS® 9.2. These locations were then overlaid onto the clipped soil map. Annual habitat preference was calculated by selecting individual vegetation polygons followed by the use of the Select by Attribute option within ArcGIS® to analyze the number of locations for an individual in certain vegetation classes. Number of locations within certain vegetation classes was recorded for all collared elk. Seasonal ranges were calculated in the same approach but using the following descriptions: winter (Sep-Mar) and summer (Apr-Aug). Annual and seasonal habitat preference was determined by taking 2 aerial locations per week from November
2006 - March 2008.
Habitat use was determined by using habitat-selection ratio (Manly et al., 2000) calculated as S = ([U + 0.001]/[A + 0.001]) where U was the observed use in a specific habitat based on all telemetry locations and A was availability of the habitat within the study area. I added 0.001 to both the numerator and denominator to prevent a value of 0
(Lopez et al., 2004; Garza, 2007). An S value of <1 showed the habitat was not selected for, a value of 1 showed the habitat was used in proportion to its availability, and a value of >1 showed the habitat was selected for.
TABLE 2.2--Error matrix of the vegetation map derived from soils data in the Glass Mountains, Texas.
Creosote- Desert Desert Evergreen Juniper Mesquite- Tobosa Classification Mariola Grassland Scrub woodland Woodland Tarbush Riparian Flats Row Total
Creosote-Mariola 14 1 0 0 1 0 0 0 16
Desert Grassland 0 30 0 2 0 0 0 0 32
Desert scrub 0 0 9 0 0 0 0 0 9
Evergreen woodland 1 0 0 17 1 0 0 0 19
Juniper woodland 0 0 0 1 7 0 0 0 8
Mesquite-Tarbush 0 2 1 0 1 7 0 1 12
Riparian 0 0 1 0 1 0 2 0 4
Tobosa flats 0 0 0 0 0 0 0 0 0
Column Total 15 33 11 20 11 7 2 1 100ª
ª Overall Accuracy = 86/100 = 86% 38
39
RESULTS--Capture--Fourteen elk (3 M, 11 F) were trapped during this portion of
the study. Bulls were captured via free range darting while cows were captured with the
aid of net guns fired from helicopters. I located the elk 947 times with 500 locations
during summer and 447 locations during winter. Cows accounted for 71.1% of all radio
locations. Two cows died as a result of unknown causes and were not used in habitat-use
analysis.
Habitat availability--The vegetation data encompassed 4,398.77 km² of the
northeast Chihuahuan Desert with 21.68 km² classified as “not surveyed”. Therefore,
areas that were not surveyed by NRCS were subtracted from total acreage before habitat use/availability calculations were run. No telemetry locations were found in the “not surveyed” portion of the map. The area of each habitat type was recorded and used for habitat use-availability ratios. Evergreen woodland encompassed the largest area
(1,120.2 km²) within the study site and comprised 25.59% of the overall vegetation.
Desert grassland covered 1,008.77 km² (23.05%) and creosote-mariola covered 600.98 km² (13.73%). Desert scrubland encompassed 571.15 km² (13.05%) and juniper woodland had an area of 462.79 km² (10.57%). Mesquite-tarbush scrubland covered
293.35 km² (6.70%). Riparian encompassed 186.47 km² (4.26%) and tobosa grassland
(133.08 km²) comprised the least amount of area in the study site (3.04%). Dominant species within habitats was also recorded (Table 2.3).
Habitat use--Throughout annual (Table 2.4; Fig 2.2), summer (Table 2.5; Fig
2.3), and winter time periods (Table 2.6; Fig. 2.4), elk habitat selection ratios showed similar results. Annually, elk exhibited the highest habitat selections for juniper woodland (S = 1.87), riparian (S = 1.41), and evergreen woodland (S = 1.15). Summer
Table 2.3--Habitat characteristics of the study area for habitat use-availability analysis in the Glass Mountains, Texas,
November 2006 – March 2008.
Area Habitat type km² Percent Woody Canopy Cover Dominance Creosote-mariola 600.98 13.73 138.1 creosote (Larrea tridentata), mariola (Parthenium incanum) Desert grassland 1,008.77 23.05 73.39 lechuguilla (Agave lechuguilla), sotol (Dasylirion wheeleri) Desert scrubland 571.15 13.05 46.45 mesquite (Prosopis glandulosa), creosote (Larrea tridentata), Evergreen woodland 1,120.2 25.59 154.45 pinion pine (Pinus cembroides) oak (Quercus grisea), juniper (Juniperus pinchotii) Juniper woodland 462.79 10.57 101.28 juniper (Juniperus pinchotii) lechugilla (Agave lechuguilla), sotol (Dasylirion wheeleri) skeletonleaf (Viguiera stenoloba) tarbush (Flourensia cernua), Mesquite-tarbush 293.35 6.7 114.26 creosote (Larrea tridentata) mesquite (Prosopis glandulosa) Riparian 186.47 4.26 169.63 brickellbush (Brickellia coulteri), mesquite (Prosopis glandulosa), little leaf sumac (Rhus microphylla) Tobosa grassland 133.08 3.04 TRª tobosa (Hilaria mutica) ª TR – trace amounts recorded 40
TABLE 2.4--Annual selection ratios of bull (M) and cow (F) elk and percent use versus availability of the landscape in the Glass Mountains, Texas, November 2006 – March 2008.
Male and Female Male Female
Habitat Type % Available % Used Sª % Used S % Used S
Creosote/Mariola 13.73 7.39 0.54 0.73 0.05 10.1 0.74
Desert Grassland 23.05 18.16 0.79 2.92 0.13 24.37 1.06
Desert Scrub 13.05 11.09 0.85 2.55 0.2 14.56 1.12
Evergreen Woodland 25.59 29.57 1.16 68.61 2.68 13.67 0.53
Juniper Woodland 10.57 19.85 1.88 20.44 1.93 19.61 1.85
Mesquite/Tarbush 6.7 6.86 1.02 1.09 0.16 9.21 1.37
Riparian 4.26 6.02 1.41 2.92 0.69 7.28 1.71
Tobosa Flats 3.04 1.06 0.35 0.73 0.24 1.19 0.39
Water 0.01 0 0.16 0 0.16 0 0.16
ª S = ([U + 0.001]/[A + 0.001]) 41
42
(A)
2 1.5 1 0.5 0 d n h iola a lats ter ar bus f m oodl tar Wa e/ w Riparian t grassland Desert scrub Tobosa Creosot Deser Mesquite/ vergreen Juniper woodland E
(B)
3 2.5 2 1.5 1 0.5 0 d n h iola a lats ter ar bus f m oodl tar Wa e/ w Riparian t grassland Desert scrub Tobosa Creosot Deser Mesquite/ vergreen Juniper woodland E
(C)
2 1.5 1 0.5 0 a d h ts ol an and a i crub ter ar s arbus m oodl /t Wa e/ e Riparian t grassland r woodl it ot Tobosa fl ser Desert een w squ e gr Creos D Junipe Me Ever
FIG 2.2--Annual habitat use-availability for bull and cow (A), bull (B), and cow
(C) elk based on S ([U + 0.001]/[A + 0.001]) values in the Glass Mountains, Texas,
November 2006 – March 2008.
TABLE 2.5--Summer selection ratios of bull (M) and cow (F) elk and percent use versus availability of landscape in the
Glass Mountains, Texas, November 2006 – March 2008.
Male and Female Male Female
Habitat Type % Available % Used Sª % Used S % Used S
Creosote/Mariola 13.73 6.6 0.48 0 0 8.71 0.63
Desert Grassland 23.05 21.8 0.95 2.48 0.11 27.97 1.21
Desert Scrub 13.05 10.4 0.8 0 0 13.72 1.05
Evergreen Woodland 25.59 28.8 1.13 76.03 2.97 13.72 0.54
Juniper Woodland 10.57 18.4 1.74 15.7 1.48 19.26 1.82
Mesquite/Tarbush 6.7 6.4 0.95 0.83 0.12 8.18 1.22
Riparian 4.26 6.8 1.6 4.13 0.97 7.65 1.8
Tobosa Flats 3.04 0.8 0.26 0.83 0.27 0.79 0.26
Water 0.01 0 0.16 0 0.16 0 0.16
ª S = ([U + 0.001]/[A + 0.001]) 43
44
(A)
2 1.5 1 0.5 0 d h an er iola bus flats t ar ar m oodl t Wa e/ w Riparian t grassland Desert scrub Tobosa Creosot Deser Mesquite/ vergreen Juniper woodland E
(B)
3.5 3 2.5 2 1.5 1 0.5 0 d h an er iola bus flats t ar ar m oodl t Wa e/ w Riparian t grassland Desert scrub Tobosa Creosot Deser Mesquite/ vergreen Juniper woodland E
(C)
2 1.5 1 0.5 0 d h an er iola bus flats t ar ar m oodl t Wa e/ w Riparian t grassland Desert scrub Tobosa Creosot Deser Mesquite/ vergreen Juniper woodland E
FIG 2.3--Summer habitat use-availability for bull and cow (A), bull (B), and cow
(C) elk based on S ([U + 0.001]/[A + 0.001]) values in the Glass Mountains, Texas,
November 2006 – March 2008.
TABLE 2.6--Winter selection ratios of bull (M) and cow (F) elk and percent use versus availability of the landscape in the Glass Mountains, Texas, November 2006 – March 2008.
Male and Female Male Female
Habitat Type % Available % Used Sª % Used S % Used S
Creosote/Mariola 13.73 8.28 0.6 1.13 0.08 11.9 0.87
Desert Grassland 23.05 14.09 0.61 3.27 0.14 19.73 0.86
Desert Scrub 13.05 11.86 0.91 4.58 0.35 15.67 1.2
Evergreen Woodland 25.59 30.43 1.19 62.75 2.45 13.61 0.53
Juniper Woodland 10.57 21.48 2.03 24.18 2.29 20.07 1.9
Mesquite/Tarbush 6.7 7.38 1.1 1.13 0.17 10.54 1.57
Riparian 4.26 5.15 1.21 1.96 0.46 6.8 1.6
Tobosa Flats 3.04 1.34 0.44 0.65 0.21 1.7 0.56
Water 0 0 0.16 0 0.16 0 0.16
ª S = ([U + 0.001]/[A + 0.001]) 45
46
(A)
2.5 2 1.5 1 0.5 0 d s and rub an and sl odl tarbush parian a flat Water oodl i os gras wo w R t n ser Desert scee per Tob Creosote/mariolaDe Juni Mesquite/ Evergr
(B)
3 2.5 2 1.5 1 0.5 0 d s and rub an and sl odl tarbush parian a flat Water oodl i os gras wo w R t n ser Desert scee per Tob Creosote/mariolaDe Juni Mesquite/ Evergr
(C)
2 1.5 1 0.5 0 d s and rub an and sl odl tarbush parian a flat Water oodl i os gras wo w R t n ser Desert scee per Tob Creosote/mariolaDe Juni Mesquite/ Evergr
FIG 2.4--Winter habitat use-availability for bull and cow (A), bull (B), and cow
(C) elk based on S ([U + 0.001]/[A + 0.001]) values in the Glass Mountains, Texas,
November 2006 – March 2008.
47 and winter displayed identical habitat selection but in different proportions (summer: juniper woodland (S = 1.74), riparian (S = 1.59), and evergreen woodland (S = 1.12); winter: juniper woodland (S = 2.03), riparian (S = 1.2), and evergreen woodland (S =
1.19)). Overall, 50% of all habitat communities were not selected for in proportion to their availability.
Despite annual and seasonal periods, habitat selections were similar in regard to overall sample size. When cow and bull elk were separated, they showed strong differences in habitat selection throughout these same time periods. Throughout the study, bulls only selected for evergreen woodland and juniper woodland while cows selected for juniper woodland and riparian areas but also selected for other habitats.
DISCUSSION--Habitat availability--Creating an accurate vegetation map of
4,377.09 km² using only soil data proved to be difficult. The RSD of an individual soil was not always accurate. The RSD is based on optimal forage conditions which may not always be achieved by many soil types. Many factors influence the vegetation of a certain area. The soil in the eastern portion of the study area may be able to support a certain vegetation community while that same soil on the western portion of the study area may not be able to accommodate that vegetation type. I found the RSD’s of the
Glass Mountain soils to be relatively accurate with certain habitat types having greater accuracy than others. When comparing the RSD to the corrected vegetation, riparian and tobosa grassland habitats were 100% accurate. Desert grassland demonstrated 97.6% accuracy and creosote-mariola scrubland was 91.5% accurate. Juniper woodland was
81.7% accurate and evergreen woodland was 77.4%. Desert scrubland illustrated 70.4% accuracy. Mesquite-tarbush scrubland was found to be the least accurate of all the habitat
48
types (44.7%). This could be due to the difficulty of identifying this habitat within the
DOQQ mosaic when comparing it to the corrected vegetation map that was created.
Without the knowledge gained through aerial observation, ground observation, and the utilization of roads surrounding the study site, the vegetation accuracy would begin to dwindle.
Classifying vegetation with the use of soils may be highly accurate within a small scale study area by only utilizing the optimal forage condition of the RSD, but when working with such a large scale as the Glass Mountains, it is imperative that the investigator have an understanding of the landscape prior to creating a vegetation map.
Following ground and aerial observation, vegetation data accuracy was 86%.
Habitat use--Elk are known to be flexible foragers but not all forage types are of equal preference (Merrill, 1994). Historically, the western portion of the Glass
Mountains was heavily utilized by livestock when compared to the eastern portion
(personal communication, B. J. Warnock, Sul Ross State University, Alpine, Texas).
This has caused many woody shrub species to dominate the eastern region. I found that the primary habitat types used by elk annually include the juniper woodland, riparian, and evergreen woodland areas; habitat types that are predominantly found on the eastern portion of the range. Elk expressed little difference throughout winter and summer when considering habitat selection.
Anderson et al. (2005) found that elk avoided areas with high woody and sedge species. This is similar to what I have found considering annual habitat use. Although elk moved throughout the eastern and western landscapes, they did not select for areas containing high amounts of woody species, but did select for semi-open areas with a mix
49
of grass and forest habitats. These habitats may offer the security needed from predation
and relief from high temperatures while still allowing adequate nutrition.
Forage quality may have influenced fine scale selection (Wilmshurst and Fryxell,
1995; Cook, 2002) throughout the 3 selected habitats. The combination of the 3 selected habitats may offer many types of forage species which may allow elk to consume the
proper nutrients needed for life processes. Annually and seasonally, juniper woodland habitat contained the largest S value. This selected habitat, which was commonly found near riparian and evergreen woodland areas, may allow for escape cover into either riparian or evergreen woodland habitats. This supports the notion that elk prefer areas of edge habitat (Thomas et al., 1979; Irwin and Peek, 1983) in the arid region of west Texas.
Riparian habitats encompassed a very minor portion of the entire landscape and may show that these are movement corridors to other selected habitat types.
Weckerly (2005) found that in a Roosevelt elk (C. e. roosevelti) population in northern California, the most used habitat types were grassy meadows and clear-cut forests with a high production of grass. This differs from my results with the 3 selected habitat types. I found that annually, elk do not prefer open grassy areas. Unsworth et al.
(1998) suggested that elk prefer closed canopy stands over open landscapes. This may suggest that habitat selection in the Glass Mountains may be based on overall canopy cover of juniper woodland and evergreen woodland habitat types.
Throughout summer and winter seasons, bull elk only selected for evergreen woodland and juniper woodland habitat types. This may show that the overall nutrient intake for bulls is higher than for cows with the greater amounts of browse species within these areas. McCorquodale (2003) found that in an arid environment in Washington,
50
bulls selected for older forest conditions which had high amounts of canopy cover. He
suggests that these habitats might be selected for within hunted population regardless of
sub-adult to adult age classes. My data is also in agreement in that the Glass Mountain
bulls are a hunted population and may also prefer these habitat types for overall predator
avoidance. Cows in this area selected for riparian habitat as well as juniper woodland but
did not select for evergreen woodland. This may show that cows do prefer some canopy
but also select for escape cover.
Many artificial feeders and watering troughs are located throughout the Glass
Mountains and were not included in analysis. These artificial feeders may have been the
reason that cow elk chose different habitats throughout the seasons. These two factors
may have biased some of the results and should be addressed with further research.
Another factor that may have biased the results was the mean radio location error (0.97 km; SD = 0.68) which ranged from 0.27-2.52 km. This may have placed certain telemetry locations within different habitats due to high location error. The breeding
season was also not analyzed in this research. Bull elk may have chosen specific habitat
types in relation to females and may have also caused bias in the results.
Riparian areas in higher elevations were also overlooked due to the scale of the
project. The mean radio telemetry error was found to be 0.97 km and may have caused
certain riparian habitats to be misunderstood. Most riparian areas in the Glass Mountains
have a width smaller than 0.97 km, causing some radio telemetry locations to be placed
in incorrect habitat communities.
The Glass Mountains are comprised of many private landowners that may share
different beliefs in regard to elk management. Regardless, this data shows the
51 importance of managing elk at the landscape scale rather than a property specific scale.
If landowners can work together in the Glass Mountains, this may benefit the success of this elk population.
MANAGEMENT IMPLICATIONS--Since elk habitat use is regulated by the need to minimize the risk of predation and thermal stress while still maximizing forage intake, it is necessary that selected habitat communities be well managed. For elk in the Glass
Mountains, it appears that net energy intake is fulfilled by riparian, juniper woodland, and evergreen woodland habitats. Management plans should focus on habitat communities with good canopy cover with a mix of grass species. Habitat communities with a high content of brushy species should be managed as well. The history of the Glass
Mountains incorporates heavy utilization of certain habitats along the western portion of the range. These habitats should be managed in a way to decrease the shrub species content and increase grass and tree cover.
Riparian habitats may be possible travel corridors to other selected areas and should be managed with the aid of all landowners. This habitat cuts through the landscape and across many individual private lands. If the private landowners work together in the Glass Mountains, they may be able to promote a healthier population.
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APPENDIX A.--Morphological measurements from elk captured in the Glass Mountains, Brewster and Pecos counties,
Texas, October 2006 - March 2007.
ID # Date Age App. weight - lbs Total length (cm) Tail length (cm) Head length (cm) Thoracic girth (cm) Ear Length (cm) Overall Condition
M1 27 Oct 06 5.5 - 6.5 750 - 800 264 12.3 48 165 R - 20.5 L - 20.5 Good
M2 28 Oct 06 2.5 - 3 500 - 550 232 12 45 152 R - 24 L - 24 Good
M3 29 Oct 06 7.5 - 8 800 - 850 269 12.2 53 148.8 R - 21.6 L - 21.7 Good
F4 10 Mar 07 2 325 139 16 45 154 R - 20 L - 20 Good
F5 10 Mar 07 8 600 267 16 51 168 R - 20 L - 20 Good
F6 10 Mar 07 3 400 246 14 45 148 R - 21 L - 21 Good
F7 10 Mar 07 6 450 249 11 46 160 R - 17 L - 16.5 Good
F8 10 Mar 07 4 450 251 12.5 49 140 R - 14.5 L - 14.0 Good
F9 10 Mar 07 3.5 350 244 15 48 146 R - 16.5 L - 15 Good
F10 10 Mar 07 3 400 258 12 51 128 R - 16.5 L - 19.5 Good
F11ª 10 Mar 07 9 500 N/A N/A N/A N/A N/A Good
F12 11 Mar 07 5 500 263 18 47 156 R - 19 L - 17 Good
F13 11 Mar 07 5 650 266 13 53 184 R - 19 L - 19 Good
F14 11 Mar 07 7 600 254 12 51 146 R - 19 L - 19 Good
ª F11 was released due to high body temperature and stress levels before morphological data was recorded
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57
APPENDIX C.--Map legend used for Figure 2.1 on page 35
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VITA
Brendan R. Witt 6519 Tico Dr. Houston, TX 77083
Education:
B.S., Natural Resource Management, Sul Ross State University, 2006
M.S., Range and Wildlife Management, Sul Ross State University, 2008
Experience:
Research Assistant, Sul Ross State University, Alpine, TX 79830
Feral hog technician, The Nature Conservancy, Ft. Davis, TX 79734
Wildland firefighter, Texas Forest Service, Ft. Stockton, TX 79735
Ranch Hand, Grizzly Ranch, Cody, WY 82414