1983 ernie p. wiggers - tdl
TRANSCRIPT
© 1983 Ernie P. Wiggers
CHARACTERIZATION OF ADJACENT DESERT
MULE AND WHITE-TAILED DEER
HABITATS IN WEST TEXAS
by
ERNIE P. WIGGERS, B.S., M.S.
A DISSERTATION
IN
AGRICULTURE
Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for
the Degree of
DOCTOR OF PHILOSOPHY
Approved
Chairman of the Committee
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(L4^ //, •X L .wZ .—
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u ccepted
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ean of the G ^ d u a t e School
May, 1983
'I)
ACKNOWLEDGEMENTS
In any study which encompasses as much t e r r i t o r y as t h i s study
did i t i s necessary to acknowledge numerous agencies and individuals
for the i r con t r ibu t ions . F i r s t , I want to thank Dr. Samuel L.
Beasom for select ing me as the research a s s i s t an t for t h i s project
and for h i s advice, support, and ed i to r i a l comments on the
manuscripts we coauthored. I want to thank my advisory committee,
Drs. J. Knox Jones, Henry A. Wright, Fred C. Bryant, and John R.
Garidino, for the i r ins t ruc t ions and comments which I believed
improved me as a profess ional . I am indebted to Scott Bebber, Larry
Howe, Austin Templer, and Jim Woods for the i r unfailing work in the
f ie ld ass i s t ing me in the col lec t ion of the data presented in t h i s
d i s s e r t a t i o n . I thank the individuals of the Texas Parks and
Wildlife Department, Soil Conservation Service, National Park
Service, and Bureau of Land Management who assis ted me in locat ing
study areas and making i n i t i a l landowner contac t s . I am appreci t ive
for the cooperation of the more than 30 west Texas ranchers who
graciously allowed me to invade the i r lands and co l l ec t the
necessary vegetat ive da t a . To the graduate students within the
Department of Range and Wildlife Management, I am grateful for the i r
fr iendship and ass i s t ance , espec ia l ly Luke Celentano and Dave Wester
for the i r help with the computer management and s t a t i s t i c a l
computation of the da t a .
i i
Funding for this study was provided by the USDA Forest Service
Rocky Mountain Forest and Range Experiment Station through the Great
Plains Wildlife Research Laboratory, Dr. Fred Stromer, Project
Leader. Research f a c i l i t i e s were provided by the Department of
Range and Wildlife Management, Dr. Henry A. Wright, Chairman.
Finally, I thank my wife, Hope, for her inspiration,
encouragement, support, and love throughout the work on my doctorate
degree.
I l l
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ii
ABSTRACT v
LIST OF TABLES vii
LIST OF FIGURES viii
CHAPTERS
I. INTRODUCTION 1
II. THE STUDY AREAS 3
III. METHODS 10
IV. ANALYSIS 15
V. RESULTS 16
Population Estimates 16
Habitat Characterization: The Trans-Pecos Region . . . . .16
Habitat Characterization: The Panhandle Region 26
VI. DISCUSSION 30
LITERATURE CITED 36
Abstract
Fourteen vegetat ive parameters and a Land Surface Ruggedness
Index (LSRI) were quantified on 306,000 ha of rangeland that
d i f f e r e n t i a l l y supported high and low dens i t i e s of mule deer
(Odocoileus hemionus crooki) and white- tai led deer (0 . virginianus
texanus) in west Texas to evaluate species-specif ic habi ta t
parameters. The only s ign i f i can t ly di f ferent (P<0.05) vegetat ive
component between the habi ta t s of the 2 species was percent woody
cover. On the high density white-tai led deer hab i t a t s , woody cover
averaged 63/E, and on the high density mule deer habi ta t s i t averaged
43%. Increases in white- tai led deer dens i t i e s were pos i t ive ly
correlated with increases in percent woody cover. The re la t ionsh ip
between woody cover and responses in desert mule deer numbers was
not s igni f icant (P>0.05), but deser t mule deer nunbers tended to
decrease as percent woody cover increased. Mule deer recent ly
disappeared from 2 areas where woody cover exceeded 75?.
The measurement of percent woody cover cor rec t ly c lass i f i ed 83
and 65% of the study areas into high and low density c l a s s e s ,
respec t ive ly , for white- ta i led deer and deser t mule deer . The
threshold value for discriminating between hab i ta t s of high or low
deer densi ty was approximately 53 and 50% woody cover for white-
t a i l ed deer and mule deer , r espec t ive ly .
V
Average LSRI values where white- ta i led deer were sighted during
ae r i a l surveys were l e s s than where deser t mule deer were s ighted.
The LSRI for mule deer ranged from 2 to 232 and for white- ta i led
deer from 0 to 136. In areas exhibi t ing a wide variance in
topographic ruggedness white- tai led deer appeared to be r e s t r i c t ed
to locat ions of l e sse r ruggedness, but mule deer were no t .
Coexistence of deser t mule deer and white- tai led deer in west
Texas i s possible because of the i r divergent habi ta t select ion for
percent woody cover and topography. However, because woody cover
can change temporally, the pos s ib i l i t y ex i s t s for competitive
exclusion to occur as deer dens i t i e s shif t in response to changes in
woody cover. (k)mpetitive exclusion apparently has occurred in west
Texas as whi te- ta i led deer have successfully supplanted mule deer in
localized a reas . Monitoring of changes in woody cover should be
used as an a p r io r i method for identifying areas where the potent ia l
for competitive exclusion e x i s t s . The use of habi ta t manipulative
prac t ices tha t can rebalance the r a t i o of preferred habi ta t s for
each deer species seems essen t ia l to ensure the continued presence
of both species in t h i s portion of the i r range.
V I
LIST OF TABLES
Page
1. Habitat component comparisons within deer density classes
and between deer species in the Trans-Pecos region,
Texas 17
2. Multiple regression models for desert mule deer and white-
tailed deer densities in the Trans-Pecos region, Texas. . . . 20
3. Correlation coefficients of multple regression model
variables determined for desert mule deer and white-tailed
deer densities in the Trans-Pecos region, Texas 22
4. Habitat component comparisons between desert mule deer and
white-tailed deer habitats in the Panhandle region of
Texas and southeastern New Mexico 27
5. Deer species-specific habitat component comparisons between
high deer density habitats in the Trans-Pecos region and
deer habitats in the Panhandle region and southeastern
New Mexico 28
Vll
LIST OF FIGURES
Page
1. Location of study areas for desert mule deer and white-
tailed deer habitat characterization in west Texas and
southeastern New Mexico 5
2. Desert mule deer and white-tailed deer densities in
relation to total percent aerial woody cover in
the Trans-Pecos region, Texas 25
Vlll
CHAPTER I
INTRODUCTION
The Trans-Pecos and Panhandle regions of west Texas accommodate
populations of deser t mule deer and white-tai led deer. Within
recent years landowners, sportsmen, and b io logis t s have expressed
concern about an apparent population decline in mule deer and an
increase in white- ta i led deer in areas t r ad i t i ona l l y considered
deser t mule deer range (Harwell and Gore 1981). Although
unsubstant iated, t h i s s i tua t ion may r e su l t from brush infes ta t ion
(Humphrey 1958, Johnston 1963, USDA 1964, Hasting and Turner 1965)
tha t now favors the white- tai led deer (Harwell and Gore 1981).
A survey of landowners in the Pecos River area indicated that
brush, as measured by changes in mesquite (Prosopis sp.) and
juniper (Juniperus s p . ) , has increased in r e l a t i ve abundance since
1900, and that white- ta i led deer have been disproport ionately
favored by t h i s increase (Wiggers 1982). Similar pat terns of white-
ta i led deer encroachment have been observed in the westcentral
United States and southern Canada (Kramer 1972). Kramer suggests
tha t the increasing dens i t i e s of woody vegetation along water
channels may have influenced a shif t in species r a t i o favoring
whi te- ta i led deer in these areas by providing habi ta t corr idors for
range expansion.
Presently l i t t l e i s known regarding the habitat requirements for
either deer species in west Texas, especial ly on sympatric ranges.
The lack of such information res tr i c t s the formulation of managonent
guidelines for possible habitat improvement for either species.
Given continued white-tailed deer encroachment, th i s knowledge i s
essential for addressing the concerns for the future status of the
desert mule deer. The objective of th i s study was to determine i f
selected habitat components di f ferent ia l ly influenced population
leve l s of desert mule deer and white-tailed deer.
CHAPTER I I
The Study Areas
Texas Parks and Wild l i fe Department (TPWD) deer d i s t r i b u t i o n maps
i n d i c a t e t h a t sympatric popula t ions of mule deer and w h i t e - t a i l e d
deer occur in the Panhandle and Trans-Pecos geographic reg ions in
west Texas (Harwell and Gore 1981, Russ 1981). Within these
r e g i o n s , s e l e c t i o n of s p e c i f i c study a r ea s which were known to
support or p rev ious ly t o have supported popula t ions of both deer
spec i e s was aided by TPWD and USDA Soil Conservation Service (SCS)
pe r sonne l . The a reas se lec ted included a l l or p a r t s of 30 p r i v a t e
r anches , 1 s t a t e and 1 f e d e r a l l y administered park in west Texas.
In a d d i t i o n , t he Mescalero Sands Area, administered by the Bureau of
Land Management (BLM), in southeas te rn New Mexico was included as a
s tudy area with the Panhandle region ( F i g . 1) . These a reas
represented 306,000 ha of sympatric or a t l e a s t adjacent d e s e r t mule
deer and w h i t e - t a i l e d deer h a b i t a t s .
In the Panhandle r e g i o n , TPWD maps i n d i c a t e t h a t deer a re
a s soc ia t ed p r imar i l y with the the Rolling P la ins Physiographic Area
(Harwell and Gore 1981, and Russ 1981). This area has a tempera te ,
sub t rop i ca l c l i m a t e , cha rac t e r i zed by long summers and dry win te r s
(Richardson e t a l . 1974). The Rolling P la ins occupies a zone
between the a r i d , d e s e r t r eg ions to the southwest and the more humid
NM
Study Areas
m Edwards Plateau
Rolling Plains
^ Mescalero Sands
Trans-Pecos
r eg ions t o the e a s t . P r e c i p i t a t i o n i s extremely v a r i a b l e , both
seasona l ly and annua l ly , but a long term annual average i s about 52
cm (Cor re l l and Johnston 1970). The major i ty occurs as r a i n during
spr ing and summer thundershowers . Snow f a l l s occas iona l ly but
u s u a l l y remains on the ground for only a few days . Extremes in
seasonal tempera tures a re e v i d e n t . From November to March s t rong ,
f a s t moving cold f ron t s can r e s u l t in pronounced and rapid drops in
d a i l y t empe ra tu r e s . The average minimum temperature for January
through March, the 3 co ldes t months, i s - 1 . 7 C. Summers are hot
with an average maximum temperature during June through August of 34
C. The l eng th .of the f ros t f ree period i s 200-220 days (Koos e t a l .
1966, Richardson e t a l . 1974).
The area i s cha rac t e r i zed by r o l l i n g topography, except in
l oca l i zed a reas where stream channel erosion has produced prominent
escarpments and canyons. So i l s are p r imar i ly deep to very shallow
c l a y , s i l t , and sandy loams under la in by a l ayer of ca l i che and
sandstone (Jacquot e t a l . 1965, Wright and Bailey 1982). Twenty
t h r e e range s i t e s were evident on the study a r e a s . Of t h e s e , 10
comprised 88% of the study a r e a s . These were, in descending order
by a r e a : deep sand, rough b r e a k s , mixedland s lopes , mixedlands, deep
h a r d l a n d s , sandy loams, sandy bot tomlands , very shal low, shallow
r e d l a n d s , and hardland s l o p e s .
The Rolling Plains are contained within the mixed grassland
vegetative type of the Southern Great Plains. Dominant woody
species include mesquite and juniper on most s o i l s , with sand
shinnery oak (Quercus havardii) and sand sagebrush (Artemisia
f i l i f o l i a ) on sandy s o i l s (Correll and Johnston 1970). Some
important subdcminant shrubs include lotebush (Zizyphus
obtusifolia) , ephedra (Ephedra sp.) , and aromatic sumac (Rhus
trilobata) (Wright and Bailey 1982). Prairie grasses include l i t t l e
bluestem (Schizachyriim scoparium) , big bluestem (Andropogon
gerardii) , sideoats grama (Bouteloua curtipendula) , and hairy grama
(B. hirsuta); with buffalo grass (Buchloe dactyloides) . tobosagrass
(Hilaria mutica) , and three awn (Aristida sp.) grasses increasing
under heavy grazing pressure (Correll and Johnston 1970).
The Mescalero Sands are located just below the western edge of
the Llano Estacado escarpment in southeastern New Mexico. The most
prominent physiological features of th i s area are 3 large, mobile
sand dunes (Smith 1971). The climate i s semi-arid with an average
rainfal l of 38 cm and a frost-free period of approximately 200 days
(Tuan et a l . 1969). The 2 major range s i t e s in this area are
sandyland and duneland.
The Trans-Pecos region includes the Trans-Pecos and the western
edge of the Edwards Plateau Land Resource Areas (Rives 1980). This
region has a warm semi-arid climate (Turner and Fox 1974, Rives
8
1980). Annual p rec ip i t a t ion i s about 30 cm, although t h i s var ies
grea t ly between years (Correll and Johnston 1970). Most of t h i s
p rec ip i t a t ion r e s u l t s from spring and summer thundershowers. Snow
accumulations are infrequent and do not represent a s ignif icant
source of moisture. The average minimum winter temperature for the
3 coldest months, January through March, i s 1.1 C. Average maximum
summer temperature i s 35 C for June through August. The length of
the frost free period i s 240-265 days (Tunner and Fox 1974, Rives
1980).
Topography cons i s t s of broad, level plateaus and ro l l ing to steep
h i l l s and canyon wal ls . Soils are shallow to deep and gravelly on
the limestone outcrops, gravelly and*loamy on the upland s i t e s , and
clayey and loamy on the flood p la ins . Concentrations of gypsum and
lime occur in many s o i l s of t h i s region (Carter and Cory 1930).
Several range s i t e s are evident in the Trans-Pecos region, but only
4 s i t e s were present on the study a reas . These were, in descending
order by a rea : steep rocky, gravel ly , deep s o i l , and bottomland.
The Trans-Pecos region i s on the eastern edge of the deser t
shrub-grass vegetat ive type. Major woody species include mesquite,
creosote bush (Larrea t r i d e n t a t a ) . tarbush (Flouren sia cernua) . and
fourwing saltbush (Atriplex canescens) (Rives 1980, Wright and
Bailey 1982). The more xeric s i t e s support arid-land plants such as
lechegui l la (Agave l e c h e g u i l l a ) , oco t i l l o (Fouquieria splendens),
and several species of yucca (Yucca sp.) (Correll and Johnston
1970). Prevalent grasses include black grama (Bouteloua eriopoda) .
alkal i sacaton (Sporobolus airoides) . tobosagrass, and burrograss
(Scleropogon brevifolius) (Bunting 1978, Rives 1980).
Ranching i s the major agricultural act ivity conducted on the
study areas in both regions. In the Panhandle region, ranching
operations u t i l i ze almost exclusively c a t t l e , whereas in the Trans-
Pecos region c a t t l e , sheep, goats, and combinations thereof are
u t i l i z e d . Since the cat t l e industry predominates in the Rolling
Plains, there i s l i t t l e effort between landowners to control
predators. However, where sheep and goats are managed in the Trans-
Pecos region extensive control efforts by landowners, primarily for
coyotes (Canis latrans) , are evident.
CHAPIER I I I
Methods
A l a t e September-early October he l i cop t e r survey was used to
determine s p e c i e s - s p e c i f i c deer d e n s i t i e s for 2 parks and 11 ranches
in the Panhandle region in 1980 and 17 ranches in the Trans-Pecos
region in 1981. Deer populat ion d e n s i t i e s for the Mescalero Sands
area were obtained from a e r i a l surveys conducted in 1979 and 1980 by
the BLM (ELM unpublished d a t a ) . All a e r i a l surveys were conducted
only during the 3 hours a f t e r sunr i se and 3 hours before s u n s e t .
During the a e r i a l survey the number of deer sighted was recorded ,
and the l o c a t i o n of each s igh t ing was marked on accompanying
topographic maps for l a t e r a n a l y s e s .
In the Panhandle r eg ion , deer popula t ions tended to be sparse and
l oca l i z ed so t h a t f l i g h t - l i n e s were concentrated in a reas where the
i n v e s t i g a t o r s f e l t the chance of s igh t ing deer was g r e a t e s t . This
procedure more e f f i c i e n t l y u t i l i z e d a v a i l a b l e f l i g h t t ime . Because
deer s i g h t i n g s were l o c a l i z e d , a study area was r e s t r i c t e d to the
area within a 2.15 km rad ius c i r c l e inscr ibed around a e r i a l
s i g h t i n g s of d e e r . The 2.15 km rad ius encompassed an area, t h a t
exceeded the average home range s ize of sedentary deer in t h i s
reg ion (Koerth 1981). S igh t ings l e s s than 2.15 km apar t were
considered to be within the same study a r e a , and t h i s combined area
10
11
c o n s t i t u t e d one study a r e a . Areas which did not over lap were
considered to be separa te study a r e a s . This procedure r e s u l t e d in
21 s tudy a r e a s in the Panhandle r e g i o n . In the Trans-Pecos region
the a e r i a l t r a n s e c t l i n e s t r aversed each e n t i r e ranch because deer
in t h i s reg ion were more numerous and more uniformly d i s t r i b u t e d .
Here each ranch was considered as a separa te study a r e a .
Vegetat ion was sampled during February through April and May
through September to determine seasonal extremes. Sampling was
r e s t r i c t e d to the Panhandle study a reas during the winter and summer
seasons of 1980 and on the Trans-Pecos study a reas in the winter and
summer of 1981. To minimize v a r i a t i o n between sample p l o t s , each
area was s t r a t i f i e d and sampled according to SCS range s i t e
c l a s s i f i c a t i o n s . Sample p lo t c e n t e r s were equa l ly spaced at 75 m
d i s t a n c e s along a randomly se lec ted t r a n s e c t through each range
s i t e . The same p l o t cen te r was used for a l l sampling procedures .
An average of 154 and 91 p l o t c e n t e r s were located and sampled per
s tudy area in the Panhandle and Trans-Pecos r e g i o n s , r e s p e c t i v e l y .
Standing biomass was sampled by c l i pp ing a l l herbaceous p lan t
ma te r i a l wi thin 0.25 m^quadrats a t each p l o t c e n t e r . All p l an t s
were sor ted in to g r a s s or forb groups and weighed to the nea res t
whole gram. Any herbaceous ma te r i a l l e s s than 1 gr in biomass was
recorded as 0.5 g r . Representa t ive samples of a l l p lan t ma te r i a l
were oven-dried (40 C) and percent mois ture content de termined.
12
Standing biomass was adjusted for moisture content and expressed as
(kg/ha) oven-dried biomass.
Percent of horizontal screening cover was measured at each plot
center for 5 height intervals on a 2.5 m x 0.15 m density board
(Nudds 1977). The proportion of area screened from a kneeling
observer in each 0.5 m interval at 15 m and 30 m distances was
estimated to 1 of 8 percentage c lasses ; 0, 1-5, 6-25, 26-50, 51-75,
76-95, 96-99, and 100 %. The mid-point value of each percentage
c lass was recorded as the percent of screening cover. This
measurement was repeated for 2 randomly selected directions from the
sample plot center. The average percent screening cover for the
0,0-1,5 m intervals was used to estimate a mean distance where total
deer screening at deer height occurred (Tanner et a l . 1978). An
identical procedure was used to determine the mean distance to total
screening above deer height using the percent screening cover for
the 1.6-2.5 m intervals . If no screening cover was measured, then
distance to total screening was recorded as 1,500 m.
Woody plant density was determined by counting stems of a l l woody
plants and cacti in 0,01 ha circular quadrats around each plot
center. Density calculations were made for each species, for al l
woody plants, and for tree species which could support a canopy
cover above deer height. In addition, the canopy diameter of
randomly selected specimens of each species on each range s i te and
13
area was r eco rded . Diameter measurements were used to c a l c u l a t e an
average canopy area assoc ia ted with each woody s p e c i e s . Average
canopy area and stem dens i t y were used to determine percent a e r i a l
cover of each woody spec i e s on a range s i t e using the following
e q u a t i o n : % a e r i a l woody cover = canopy area (m ) * dens i ty
( s t ems /ha) /10 ,000 mVha *100, The sum of the percent a e r i a l cover
for a l l woody spec i e s equal led the t o t a l percent a e r i a l woody cover
for a range s i t e , and the sum for a l l the t r e e species equalled the
percent a e r i a l t r e e cover . Canopy diameter was included as a
v e g e t a t i v e measurement only for the Trans-Pecos study a r e a s .
Topographic ruggedness was determined by c a l c u l a t i n g a Land
Surface Ruggedness Index (LSRI) a t each map loca t i on of deer
s i g h t i n g s recorded during the he l i cop t e r survey. LSRI va lues were
used to a s s e s s land ruggedness as a h a b i t a t f ea tu re for each deer
s p e c i e s . The LSRI was determined using a do t -g r id composed of 96
uniformly spaced do t s on a c i r c l e of t r a n s p a r e n t p l a s t i c sheet ing
which represented a 40 ha area on topographic maps. The cen te r of
t h i s gr id was ove r l a id to match the point marked as a deer s igh t ing
on the topographic map. The number of dot-contour l i n e
i n t e r s e c t i o n s for each s igh t ing was counted and recorded as the LSRI
v a l u e . Because twice and four t imes the number of contour l i n e s a re
requi red to d e p i c t the r e l i e f for a given area using 3.04 versus
6.10 and 12.20 m contour i n t e r v a l s , r e s p e c t i v e l y , a l l LSRI va lues
were s tandardized to t h a t expected for the 3.04 m contour i n t e r v a l s .
14
This was accomplished by multiplying the LSRI value by a correction
factor equal to the contour l ine interval of the map divided by 3.04 m.
CHAPTER IV
Analysis
Mean vegetat ive measurements from sample p lots within range s i t e s
were determined for each study area. Mean values were 'weighted' in
proportion to the area occupied by each range s i t e in that study
area. The data for the Mescalero Sands study area was included with
the data for the study areas in the Panhandle region during
analyses . Because of ex i s t ing differences between habitat and
envirorment, data for the Panhandle and Trans-Pecos regions were
analyzed independently. Population d e n s i t i e s were used as
indicators of habitat preference, assuming high d e n s i t i e s were «
ref lect ive of high habitat preference. The low deer densit ies
determined for the Panhandle region precluded their separation into
low and high density c lasses for habitat contrast evaluations.
Instead, a l l observations were assigned a low density
c las s i f i ca t ion . Deer densi t ies in the Trans-Pecos region were 2 2
grouped into low (<8.0 deer/0.4 km ) and high O8.0 deer/0.4 km )
density c lasses for analyses, A IXincan's multiple range test was
used to determine i f significant differences existed between
parameters in desert mule deer and white-tailed deer habitats within
deer density c la s se s , A discriminant analysis was used to determine
i f selected habitat parameters could accurately c lass i fy habitats
into low or high deer density c la s se s ,
15
CHAPTER V
Resul ts
Population Estimates
Densi ty e s t i m a t e s in the Trans-Pecos region ranged from 2 - 2
0 . 0 - 2 9 . 0 / 0 , 4 km (X=5,5) for d e s e r t mule deer and 0 .3 -27 .0 /0 .4 km
(X=10.3) for w h i t e - t a i l e d d e e r . Although mule deer were not
observed on 2 a r e a s , landowner records i nd i ca t e t h a t t h i s spec ies
had occupied these a reas within the past 40 years (W. A. Wroe,
Personal Communication), Population es t imates for the Panhandle
region were lower and narrower in range , 0 .6 -9 .1 /0 .4 km^ (Y=3.0) and 2 —
0 . 6 - 8 . 9 / 0 . 4 km (X=3.3) for mule deer and wh i t e - t a i l ed dee r , r e s p e c t i v e l y .
Habi ta t Clharacter iza t ion: The Trans-Pecos Region
In the Trans-Pecos r eg ion , percent woody cover was the only
v e g e t a t i v e parameter which was s i g n i f i c a n t l y d i f f e r e n t (P<0.05)
between h a b i t a t s occupied by mule deer and wh i t e - t a i l ed deer (Table
1 ) . Aerial woody cover averaged 63% on a reas support ing high whi te-
t a i l e d deer d e n s i t i e s . This value was s i g n i f i c a n t l y g rea te r (P<0.05)
than the 43% a e r i a l woody cover determined on a reas support ing high
d e n s i t i e s of mule deer (Table 1) . Conversely, woody cover averaged
43% on the low d e n s i t y w h i t e - t a i l e d deer h a b i t a t s and 56% on the low
d e n s i t y d e s e r t mule deer h a b i t a t s . A s i g n i f i c a n t d i f fe rence
16
17
Table 1. Habitat component comparisons within deer density classes and
between deer species in the Trans-Pecos region, Texas. Measurements
followed by a different lower case letter are significantly different
(P< 0.05).
Habitat component
Forage biomass. summer (kg/ha)
Grass biomass. summer (kg/ha)
Forb biomass. Slimmer (kg/ha)
Forage biomass, winter (kg/ha)
Grass biomass. winter (kg/ha)
Forb biomass, winter (kg/ha)
Total woody density (stems/ha)
Tree density (stems/ha)
Total woody cover (%)
Tree cover (%)
n <a a•nr•« tn rlosur(
High Mule deer
507 a
315 a
192 a
365 a
196 a
169 a
3,937 a
649 a
43 a
20 a
a 194 a
deer
N
1 5
5
5
5
5
5
5
5
5
5
5
density White-tailed deer
860 a
524 a
336 a
690 a
256 a
434 a
3,044 a
811 a
63 b
35 a
151 a
N
8
8
8
8
8
8
8
8
8
8
8
Low Mule deer
820 a
507 a
313 a
690 a
308 a
382 a
3,321 a
732 a
56 a
31 a
152 a
deer
N
12
12
12
12
12
12
12 3
12
12
12
12
density White-ta deer
611 a
386 a
225 a
508 a
291 a
217 a
,909 a
616 a
43 a
21 a
176 a
ilec N
9
9
9
9
9
9
9
9
9
9
9
0.0-0.5 m strata, summer (m)
Distance to closure 943 a 1.6-2.5 m strata, summer (m)
Distance to closure 377 a 0.0-1.5 m strata, winter (m)
Distance to closure 917 a 1.6-2.5 m strata, winter (m)
893 a 8 904 a 12 936 a 9
5 387 a 8 317 a 12 288 a 9
781 a 8 863 a 12 967 a 9
18
Table 1.—Continued
High deer density Low deer density Mule White-tailed Mule White-tailed
Habitat component deer N deer N deer N deer N
LSRI 30 a 615^ 29 a 779 40 a 122 31 b 242
1 2 Number of study areas; Number of deer sighting locations,
19
(P<0,05) was determined between the average LSRI values for mule
deer versus white- ta i led deer sightings on low deer densi ty areas
(Table 1) . Overall LSRI measurements of mule deer sightings were
greater and had a greater range (2-232) than those of white-tai led
deer (0-136).
Within deer species , t o t a l herbaceous biomass and grass biomass
in the summer were s igni f icant ly lower (P<0.05) on the high density
versus the low densi ty mule deer hab i t a t s . Canopy cover for a l l
woody plants and for t r ee s only were s igni f icant ly greater (P<0.05)
on high versus low densi ty white- ta i led deer hab i t a t s . The
remaining habi ta t parameter measurements characterized high density
whi te- ta i led deer habi ta t s as having greater amounts of both
screening cover and herbaceous plant material than did low density
whi te- ta i led deer h a b i t a t s . Conversely, screening cover and
herbaceous biomass was greater on low mule deer density habi ta t s
than on high mule deer densi ty h a b i t a t s .
Total percent ae r i a l woody cover and percent aer ia l cover of the
t r ee species accounted for 63% of the variat ion in white-tai led deer
dens i t i e s in a stepwise mult iple regression model (Table 2) , Total
ae r i a l woody cover accounted for 48% of the va r ia t ion , but the
increase in the regression coeff ic ient when percent t ree ae r ia l
cover was included was s ign i f i can t . Two dif ferent var iables
resul ted vrtien mule deer densi ty was used as the dependent variable
20
Table 2. Multiple regression models for desert mule deer and white-
tailed deer densities in the Trans-Pecos region, Texas.
Dependent variable = Mule deer
density
Intercept
B value
3.961
P F R P F
0.55 0.0036
Grass biomass, summer (kg/ha) -0.030 0.0016
Distance to closure 1.6-2.5 m strata, summer (m)
0.017 0.0042
Dependent variable = White-tailed
deer density
0.63 0.0009
Intercept
Total woody cover
Tree canopy cover
-10.900
56.832
-32.102
0.0004
0.0291
21
(Table 2 ) . The measurements of summer grass biomass and mean
dis tance to closure at deer height accounted for 55% of the
var ia t ion in mule deer d e n s i t i e s .
Correlations between regression model variables and species-
specif ic deer dens i t i e s are given in Table 3. Total percent aer ia l
woody cover was the most highly correlated parameter. Increases in
percent ae r i a l woody cover were s igni f icant ly (P<0.05) correlated
with increases in white-tai led deer d e n s i t i e s . Mule deer dens i t i es
were negatively associated with percent aer ia l woody cover, although
t h i s was not a s igni f icant (P>0.05) re la t ionsh ip . No habitat
parameters were s ignif icanty correlated with mule deer dens i t i e s .
The strongest r e la t ionsh ip with mule deer dens i t ies was indicated
for standing grass biomass during the summer, and t h i s was an
inverse r e l a t i onsh ip . In addit ion, mule deer dens i t i es were
inversely correlated with increases in white-tailed deer dens i t i e s .
Percent ae r i a l woody cover was inversely related to to t a l woody
density (r=-0,47, P<0,05) but strongly correlated with the dominant
brush species , mesquite (r=0.80, P<0.001). Although not
s ign i f i can t , the percent mesquite aer ia l cover was posi t ively
re la ted with increases in white-tai led deer numbers and inversely
related with increases in mule deer numbers.
Because aer ia l woody cover was the only vegetative parameter
measured that was s ign i f ican t ly d i f ferent between deer species, i t
22
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23
was further investigated to determine i f i t could be used to
discriminate between deer densi ty c l a s se s . The measurement of t o t a l
percent ae r i a l woody cover was successful in correc t ly classifying
65 and 83% of the observations for mule deer and white-tailed deer,
r e spec t ive ly , into deer densi ty c lasses (Fig, 2 ) . Of the 6 wrong
c l a s s i f i c a t i o n s for mule deer where the discriminate c lass i f i ca t ion
did not agree with those according to observed deer d e n s i t i e s , 5
occurred when low densi ty observations were placed in the high
densi ty c l a s s . The apparent s ingle threshold value for
discriminating between deer density c lasses occurred at about 50%
t o t a l woody cover. Habitats supporting a percent aer ia l woody cover
l e s s than 50% were c lass i f ied into high mule deer density c l a s ses .
Of the 3 areas supporting 75% woody cover or more, mule deer have
disappeared on 2 a reas , and thei r density was l ess than 4/0.4 km^ on
the other a rea .
The threshold value used to discriminate between white-tai led
deer densi ty c lasses occurred at 53% to ta l aer ia l woody cover.
Areas where percent ae r ia l woody cover was greater than th i s were
c lass i f ied as high white- tai led deer densi ty h a b i t a t s . Two of the 3
misc lass i f i ca t ions for white-tai led deer resulted when high deer
densi ty observations were c lass i f ied to the low densi ty c l a s s . All 2
whi te- ta i led deer densi ty est imates that exceeded 20 deer per 0.4 km
occurred when t o t a l ae r ia l woody cover exceeded 65% and they were
co r rec t ly c l a s s i f i e d .
24
25
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26
Habi ta t C h a r a c t e r i z a t i o n : The Panhandle Reg ion
In the Panhandle r e g i o n , no s i g n i f i c a n t (P>0.05) d i f f e rences were
determined between the vege t a t i ve components of mule deer and whi te-
t a i l e d deer h a b i t a t s (Table 4 ) . A s i g n i f i c a n t (P<0.05) d i f fe rence
between deer spec ies was shown only for the LSRI value associa ted
with each s igh t ing (Table 4 ) . Not only was the mean LSRI
measurement a s soc ia ted with mule deer l o c a t i o n s s i g n i f i c a n t l y higher
than those for w h i t e - t a i l e d dee r , but the LSRI range was much
broader (10-176 and 0-90, r e s p e c t i v e l y ) and i t s maximum value was
almost twice as l a r g e as t h a t for wh i t e - t a i l ed dee r .
No s i g n i f i c a n t (P>0.05) c o r r e l a t i o n s or regress ion models could
be determined between s p e c i e s - s p e c i f i c deer d e n s i t i e s and h a b i t a t
measurements in the Panhandle r eg ion . The s t ronges t r e l a t i o n s h i p
was ind ica ted between LSRI measurements and mule deer d e n s i t i e s
( r = 0 . 6 l , P<0.10) ,
Evaluat ions of deer h a b i t a t s in the Panhandle were attempted by
comparing h a b i t a t measurements from t h i s region to measurements
determined on the high d e n s i t y deer h a b i t a t s in the Trans-Pecos
region (Table 5 ) . Comparisons reveal dramatic d i f f e rences which
might be i n d i c a t i v e of h a b i t a t q u a l i t y between the 2 r e g i o n s . Most
no t ab l e were the s i g n i f i c a n t (P<0.05) or otherwise s u b s t a n t i a l
d i f f e r e n c e s in seasonal forb product ion . During the winter season.
27
Table 4. Habitat component comparisons between desert mule deer and
white-tailed deer habitats in the Panhandle region of Texas and south
eastern New Mexico. Measurements followed by a different lower case
letter are significantly different.
Habitat component Mule deer N White-tailed deer N
Forage biomass, summer 579 a 9 538 a 12 (kg/ha)
Grass biomass, summer 436 a 9 456 a 12 (kg/ha)
Forb biomass, summer 143 a 9 83 a 12 (kg/ha)
Forage biomass, winter 270 a 9 378 a 12 (kg/ha)
2 Grass biomass, winter 208 a 9 327 b* 12 (kg/ha)
Forb biomass, winter (kg/ha)
Total woody density 16,806 a 9 21,975 a 12 (stmes/ha)
Tree density (stems/ha)
Distance to closure, 0.0-1.5 m strata, summer (m)
579 a
436 a
143 a
270 a
208 a
62 a
16,806 a
617 a
283 a
9I
9
9
9
9
9
9
9
9
LSRI
50 a 12
996 a 12
177 a 12
779 a 9 818 a 12
376 a 9 204 a 12
Distance to closure, 1.6-2.5 m strata, summer (m)
Distance to closure, 0.0-1.5 m strata, winter (m)
Distance to closure, 1,016 a 9 1,028 a 12 1.6-2.5 m strata, winter (m)
81 a 191^ 19 b** 12
^Number of study areas; * = P<0.10, ** = P<0.01; ^Number of deer
sightings.
28
Table 5. Deer species-specific habitat component comparisons between
high deer density habitats in the Trans-Pecos region and deer habitats
in the Panhandle region and southeastern New Mexico. Measurements
followed by a different lower case letter are significantly different.
Mule deer White-tailed deer
Habitat component Trans-Pecos Panhandle Trans-Pecos Panhandle
Forage biomass, summer (kg/ha)
Grass biomass, summer (kg/ha)
Forb biomass summer (kg/ha)
Forage biomass winter (kg/ha)
Grass biomass, winter (kg/ha)
Forb biomass, winter (kg/ha)
Total woody density (stems/ha)
Tree density (stems/ha)
Distance to closure, 0.0-1.5 m strata, summer (m)
Distance to closure, 1.6-2.5 m strata, summer (m)
Distance to closure, 0.0-1.5 m strata, winter (m)
Distance to closure, 1.6-2.5 m strata, winter (m)
LSRI
507 a
315 a
192 a
365 a
196 a
169 a
3,937 a
649 a
194 a
579 a
436 a
143 a
270 a
208 a
62 b
16,806 a
617 a
283 a
943 a
377 a
917 a
30 a
779 a
376 a
1,016 a
81 b***
860 a
524 a
336 a
690 a
256 a
434 a
3,044 a
811 a
151 a
893 a
387 a
781 a
29 a
538 a
456 a
83 b***'
378 a
327 a
50 b*
21,975 a
996 a
177 a
818 a
204 a
1,028 a
19 b**
* = P<0.10; ** = P<0.05; *** = P<0.01.
29
mean forb production on the high density white-tailed deer habitats
in the Trans-Pecos region were more than 800% greater than for
white-tailed deer habitats in the Panhandle region. Although not as
dramatic, similar dispari t ies occurred when mule deer habitats were
compared. In addition, LSRI measurements were significantly
different (P<0,05) for both deer species between regions.
CHAPTER VI
Discussion
Mean measurements of 63% woody cover on areas supporting high
w h i t e - t a i l e d deer d e n s i t i e s and 43% on areas supporting low
d e n s i t i e s agree s t rong ly with the 60% and 43% brushy cover reported
for high and low d e n s i t y w h i t e - t a i l e d deer h a b i t a t s in south Texas
( S t e u t e r and Wright 1980) . Approximately 53% woody cover appears
essen t i a l before high dens i t i e s of white-tailed deer can be expected
on rangeland in southwest Texas. However, as indicated by the
missed c l a s s i f i c a t i ons in the discriminate analys is , percent aer ia l
woody cover alone does not ensure high deer d e n s i t i e s . Steuter and •
Wright (1980) reported that brushy cover accounted for 67% of the
va r ia t ion in white- tai led deer dens i t i e s in south Texas. This value
approximated the percent determined for the white-tailed deer in the
Trans-Pecos region. Other inves t iga tors have reported the
requirements for suff ic ient brushy cover by white-tailed deer on
rangeland in Texas (Horejsi 1973, McMahan and Ingl is 1974, Ingl is e t
a l . 1978)
The r e l a t ionsh ip between brushy cover and desert mule deer
populations i s l e s s apparent because of the wide var ia t ions in the
response of mule deer dens i t i e s to that habitat parameter. But, the
30
31
data strongly suggest that desert mule deer can maintain higher
population nunbers in areas where there i s substantially lower
amounts of aerial woody cover than can white-tailed deer. Short
(1977) concluded that the mule deer has benefited from brush
infestation in i t s range since many of the forage species i t uses
are those that have invaded and proliferated on the semidesert
grasslands. This benefit apparently ex is t s only i f l e s s than 50%
woody cover i s maintained on the rangeland. If woody cover
development continued with brush infestation, then a shift in
habitat characteriztics favoring white-tailed deer would be
expected.
The wide variations in mule deer densit ies in response to
different l eve l s of woody cover indicates that this deer has l e s s
specific requirements for woody cover than white-tailed deer.
However, the presence of high densit ies of white-tailed deer on all
areas with high amounts of woody cover precluded a definit ive
determination since i t could not be distinguished v*iether habitat
preferences alone or the presence of white-tailed deer restricted
mule deer occupation. Kramer (1971) observed interactions between
Rocky Mountain mule deer (0, h, hemionus) and white-tailed deer (fi,
V, dacotensis) on overlapping range and concluded that negative
aggressive behavior was not prevalent between the 2 deer species.
If similar interactions are assimed for sympatric populations in
west Texas, then the conclusion that habitat selection alone
32
partition the 2 deer species on their range i s strengthened.
The recent disappearance of mule deer on 2 areas currently
supporting high white-tailed deer densit ies and a high percent woody
cover indicates that white-tailed deer can replace desert mule deer
in marginal mule deer habitat (MacArthur 1958). Similarly, i t has
been shown that mule deer can replace white-tailed deer given the
proper habitat changes (Anthony and anith 1977).
As a vegetative component, woody cover can be influenced by a
variety of environmental and man-made actions which can alter i t s
structure. During response to these actions, alterations in the
percent aerial woody cover may result in habitat selection shifting
between deer species so that a temporary opportunity for
interspecif ic competition and competitive exclusion exists (Anthony
and anith 1977). A survey by Wiggers (1982) suggests that this type
of exclusion has occurred in the Pecos River area of Texas, They
reported that brush infestation has continued throughout this
century resulting in a shift in habitat characteristics which now
favors the white-tailed deer. As a resu l t , white-tailed deer have
expanded into new locations in this area at a rate twice that of
mule deer. Further, the extirpation rate of mule deer on individual
ranches was 700% greater than that for white-tailed deer. Thus, i t
appears that competitive exclusion by white-tailed deer has occurred
and may s t i l l be occurring in this area as a result of habitat
33
preference sh i f t s from increases in aerial woody cover. The
opposite trend in habitats and population dynamics between desert
mule deer and Coues white-tailed deer (fi, v , couesi) was reported by
Anthony and Smith (1977) in southern Arizona. They attributed this
occurrence to an upward shift in altitude of the desert shrub
vegetational zone favored as habitat by the desert mule deer and a
concurrent retreat upward in altitude of the oak woodland,
chaparral, coniferous forest zone favored as habitat by the white-
tai led deer. The desert shrub type was characterized as being
overgrazed and supporting lesser abundance of grasses and herbaceous
plant material than the vegetation zones favored by white-tailed
deer. Thus, the study by Anthony and Smith (1977) collaborates my «
findings that desert mule deer habitats differ from white-tailed
deer habitats by the amount and structure of the existing
vegetation.
The s ignif icantly greater LSRI values for locations where mule
deer were sighted compared to where white-tailed deer were sighted
indicated that mule deer can occupy areas of greater topographic
ruggedness. Other investigators have proposed land ruggedness as a
possible habitat partitioning factor (Kramer 1972, Krausman 1978).
However, their observations were based on primarily subjective
evaluations of topography. Thus, additional investigations where
land surface ruggedness i s quantitatively analyzed throughout the
range of deer habitat overlap are needed to determine i t s full
34
importance and the specific conditions under which i t becomes a
factor.
The lower population estimates of both deer species in the
Panhandle region probably ref lects a generally lower habitat quality
for deer. Because forbs comprise a major proportion of the diet of
each species (Chamrad and Box 1968, Anderson et a l . 1965, Short
1977. Sowell 1981), the lower habitat quality in the Panhandle
region may be a reflection of the low forb production. Lower forb
production may also account for the low nutritional plane determined
for mule deer in this region (Sowell 1981). A similar nutritional
plane would be expected for white-tailed deer because of the diet
s imilarity of the 2 deer species (Krausman 1971, Kramer 1972,
Anthony and Smith 1977).
The contributions of other factors in restricting deer population
growth in th is region, such as coyote predation or the
interrelationship between predation and habitat quality, i s not
known but warrants further investigations. Studies have shown
coyotes to be a major mortality factor of deer fawns in Texas (Cook
et a l . 1971, Beasom 1974). Given already low deer dens i t ies , a
skewed predator-prey ratio in favor of the coyote might surppress
deer populations in this region (Mech 1970, Connolly 1978).
35
Kramer (1972) concluded that since large scale coexistence of
mule deer and white-tailed deer occurs, then each species must
occupy divergent niches to ensure minimum competitive overlap. The
determination of 2 habitat selection differences between mule and
white-tailed deer on overlapping range in west Texas supports
Kramer's conclusions of divergent niches between these 2 wildlife
species . Coexistence of mule and white-tailed deer in west Texas i s
possible because of differences in each deer's habitat selection for
percent aerial woody cover and topographic ruggedness. Therefore,
dual management of these 2 deer species i s possible in areas of
overlap in west Texas. Since percent aerial woody cover may change
temporally due to a variety of factors, monitoring of th i s habitat
component seems essential for proper deer management. Chronic
monitoring should be used to determine the rate at which preferred
habitat of each deer i s shrinking or expanding, and to identify
areas where the opportunity for competitive exclusion e x i s t s .
Further, management actions designed to reverse trends of continued
woody cover development may become necessary to ensure that
preferred desert mule deer habitat remains, and that this species
remains a prominent big game animal on this portion of i t s range.
LITERATURE CITED
Anderson, A, E . , W. A. Snyder, and G. W, Brown, 1965. Stomach
^ con ten t a n a l y s i s r e l a t e d to condi t ion in mule dee r , Guadalupe
Mountains, New Mexico. Journal of Wildl i fe Management.
29:352-366.
Anthony , R. G., and N, S, Smith. 1977. Ecological r e l a t i o n s h i p s
between mule deer and w h i t e - t a i l e d deer in southeas tern Arizona,
Ecological Monographs, 47:255-271,
Beasom, S. L, 1974. Rela t ionships between predator removal and
w h i t e - t a i l e d deer net p r o d u c t i v i t y . Journal of Wildl i fe
Management. 38:854-859-
Bunting, S. C. 1978. The vege ta t ion of the Guadalupe Mountains.
D i s s e r t a t i o n . Texas Tech Univers i ty , Lubbock, Texas, USA.
C a r t e r , W. T. , and V. L. Cory. 1930. So i l s of the Trans-Pecos,
Texas and some of t h e i r vege t a t i ve r e l a t i o n s h i p s . Transact ions
of the Texas Academy of Science . 15:19-37.
Chamard, A. D. and T. W. Box. 1968. Food h a b i t s of wh i t e - t a i l ed
deer in south Texas. Journal of Range Management. 21:158-164.
Connolly, G. E. 1978. Predators and predator c o n t r o l . Pages
369-394 in J . L. Schmidt and D. L. G i l b e r t , e d i t o r s . Big Game
of North America, Ecology and Management. Stackpole Books,
Har r i sbu rg , Pennsylvania , USA.
36
37
Cook, R, S , , M, White, D, 0, T ra ine r , and W. C, Glazener. 1971.
Mor t a l i t y of young w h i t e - t a i l e d deer fawns in south Texas.
Journal of Wild l i fe Management. 35:47-56.
C o r r e l l , D, S . , and M. C, Johnston. 1970. Manual of the vascular
p l a n t s of Texas, The Texas Research Foundation, Renner, Texas,
USA,
Harwell , W, F , , and H, G. Gore, 198I. Whi te - ta i led deer
popula t ion t r e n d s . Job Performance Report. Federal Aid Project
No. W-IO9-R-4. Job No. 1, Texas Parks and Wildl i fe Department,
Aus t in , Texas, USA,
Has t ing , J , R,, and R, M. Turner . 1965. The changing m i l e .
Univers i ty of Arizona P re s s , Tucson, Arizona, USA.
H o r e j s i , ' R. G. 1973. Influence of brushlands on wh i t e - t a i l ed deer
d i e t s in North-Central Texas. Thes i s . Texas Tech Univers i ty ,
Lubbock, Texas, USA.
Humphrey, R.R. 1958. The d e s e r t g r a s s l a n d . A h i s t o r y of
v e g e t a t i o n a l change and an a n a l y s i s of c a u s e s . Botanical
Review. 24:193-252.
I n g l i s , J , M,, B, A, Brown, C. A, McMahah, and R. Hood, 1978.
Deer-brush r e l a t i o n s h i p s on the Rio Grande Pla ins of Texas.
Federal Aid Pro jec t No. W-84-R. Final Report. Texas Parks and
Wi ld l i fe Department, Aust in , Texas,USA.
Jacquot , L. T . , L. C. Geiger , B. R. Chance, V. D. Woods, D. A.
Leath, and L. C. limke. 1965. Soil survey of Armstrong County,
Texas. United S t a t e s P r in t ing Off ice , Washington, D. C , USA.
38
Johns ton , M, C, I963. Past and present g ras s l ands of southern
Texas and no r thea s t e rn Mexico. Ecology 44:456-466,
Koos, W, M,, L, A. Putman, and W, D. Mi t che l l . 1966. Soil survey
of Crosby County , Texas. United S ta t e s Pr in t ing Off ice ,
Washington, D. C , USA.
Koerth, JR. , B. H. 1981. Habi ta t u se , herd ecology, and seasonal
movements a f mule deer in the Texas Panhandle. Thes i s . Texas
Tech U n i v e r s i t y , Lubbock, Texas, USA.
Kramer, A. 1971. I n t e r s p e c i f i c behavior and d i spers ion in a
popula t ion of mule and w h i t e - t a i l e d dee r . Thes i s . Univers i ty
of A lbe r t a , Edmonton, Alber ta , Canada.
Kramer, A. 1972. A review of the ecologica l r e l a t i o n s h i p s between
mule and w h i t e - t a i l e d d e e r . Occassional Paper No. 3. Alberta
Fish and Wild l i fe Div is ion , Edmonton, Alber ta , Canada.
Krausman, P. R. 1978. Forage r e l a t i o n s h i p s between two deer
s p e c i e s in Big Bend National Park, Texas. Journal of Wildl i fe
Management. 42:101-107.
MacArthur, R. H. 1958. Population ecology of some warblers of
n o r t h e a s t e r n coni ferous f o r e s t . Ecology 39:599-619.
McMahan, C. A., and J . M. I n g l i s . 1974. Use of Rio Grande Plain
brush types by w h i t e - t a i l e d d e e r . Journal of Range Management.
27:369-374.
Mech, L. D. 1970. The wolf: The ecology and behavior of an
endangered s p e c i e s . Natural His tory P re s s , New York, New York,
USA.
39
Nudds, T. 1977. (Quantifying the vege ta t ion s t r u c t u r e of w i l d l i f e
cove r , Wildife Socie ty Bu l l . 5:113-117.
Richardson. W, E. , J . Hajek, E. Blakley, and C, Nei t sch . 1974.
Soi l survey of Co t t l e County, Texas. United S t a t e s Pr in t ing
Off ice , Washington, D. C , USA.
Rives , J . L, 1980, Soil survey of Pecos County, Texas, United
S t a t e s P r in t ing Off ice , Washington, D, C.,USA.
Russ, W. B, 1981. Big game harves t regula t ions-mule d e e r . Job
Performance Report . Federal Aid Project No. W-109-R-4. Job ik>,
5. Texas Parks and Wildl i fe Department, Aust in, Texas, USA.
Shor t , H. L. 1977. Food h a b i t s of mule deer in a semidesert
g rass - sh rub d e s e r t . Journal of Range Management. 30:206-209.
Smith, C. B. 1971. Mescalero Sands Natural Studies Plan. The
Natural His tory Museum and Paleo-Indian I n s t i t u t e . Eastern New
Mexico Un ive r s i t y . P o r t a l e s , New Mexico, USA.
Sowell , B. F. 1981. Nu t r i t i ona l q u a l i t y of mule deer d i e t s in the
Texas Panhandle, Thes i s . Texas Tech Univers i ty , Lubbock,
Texas, USA.
S t e u t e r , A. A., and H. A. Wright . 1980. Whi te - ta i led deer
d e n s i t i e s and brush cover on the Rio Grande P l a i n . Journal of
Range Management. 33:328-330.
Tanner, G. W., J . W. I n g l i s , and L. H. Blankenship. 1978. Acute
impact of h e r b i c i d e s t r i p t rea tment on mixed brush w h i t e - t a i l e d
deer h a b i t a t on the nor thern Rio Grande P l a i n . Journal of Range
Management. 31:386-391.
40
Tuan, Y., C, E, Everard, and J , G, Widdison, 1969, The c l imate of
New Mexico. S t a t e Planning Off ice , Santa Fe, New Mexico, USA.
Turner , A, J . , and R, E, Fox. 1974. Soil survey of T e r r e l l County,
Texas. United S t a t e s P r in t ing Off ice , Washington, D. C , USA.
Wiggers, E. P . , S.L. Beasom, W.B. Russ, and S. H. Soro la . 1982.
Recent changes in woody brush and deer abundance and
d i s t r i b u t i o n along the Pecos River, Texas. In P res s , The
Wi ld l i f e Socie ty B u l l e t i n .
Wright , H. A,, and A, W, Bai ley , 1982, F i re ecology, John Wiley
and Sons, New York, New York, USA,
United S t a t e s Department of Agr i cu l t u r e . 1964. Grassland
r e s t o r a t i o n , the Texas brush problem. United S ta t e s Department
of A g r i c u l t u r e , Soil Conservation Serv ice , Temple, Texas, USA.