CALI:F'CRnA STATE UNIVERSITY I NOR'lHRIIXiE
'!HE DISTRIBUTICN I REIATIVE
DENSITIES AND HABITAT
~
CIATIOOS OF THE DE5ERr 'IDR'.roiSE I GOPHERUS .AGASSIZ I
I
IN NE\7ADA
A thesis subnitted in partial satisfaction
of the
~ts
for the degree
r.msTER OF SCIElO IN Biaux;y
by
Alice Elizabeth Karl
January, 1983
Th;i;: ;;;;;;izabeth
Karl is approved:
Andrew Starrett
Maxwell
California State University, Northridge
ii
ACKNOWLEDGEMENTS
I am indebted to my major professor, Dr. Anthony
Gaudin, for his encouragement and contagious enthusiasm
and for his tremendous influence in my choice of careers.
I thank him also for his valuable comments on this and
earlier manuscripts.
I am also indebted to Dr. Kristin Berry for her
enormous support and technical assistance in the early
phase of my studies on Gopherus agassizi.
I thank Bill Mautner for unselfishly donating many
hours to editing earlier reports, which enabled me to
prepare this manuscript with greater ease.
I also thank
the Contract Officer's Approved Representative during the
major portion of this project, Mark Maley, for his
patience and genuine concern for G. agassizi.
I am grateful to the remaining members of my thesis
committee, Drs. Joyce Maxwell and Andrew Starrett, for
their comments on this manuscript and their generosity in
devoting time to my degree completion.
I also thank Dave
Pulliam for providing data on grazing systems in Nevada
and Drs. Jim Dole and Richard Swade for their advice concerning statistical analyses.
I extend my gratitude to the Las Vegas District
Office of the Bureau of Land Management (Contract No.
iii
YA-512-CT9-90) for funding a substantial portion of this
project and to Biosystems Analysis, Inc., and the AFRC for
partial funding of the project.
My special thanks is extended to Paul and Wily Melograno for their all-too-infrequent good company and to the
people who supported me, not only during this project, but
during my education at California State University, Northridge as well.
Finally, I am indebted to my parents, Robert and
Alice, without whose financial and emotional support I
could not have completed this phase of my education.
iv
TABLE OF CONTENTS
ACKNOWLEDGEMENTS. • . . • . . . . . • . . . . . . . . . • . . . . . . . • . . . . . . . iii
~
LIST OF TABLES .. • • . . . . . . . . • . . . . • . . . . . . . . . . . .
....
e
••
vii
LIST OF FIGURES . . . . . . . . • • • . • . • . • . . . . . . . " . . . . . . . . • . . . viii
ABSTRACT . . . . • . . . . • . . . • . . . . . . • . . . . . . • • . . . • . . . "' • . . . . . .
INTRODUCTION . .•.
e:
•••••••••••••••
Ill
••••
~~
..............
.
STUDY AREA. . . • • . . . . • . • . • . . • . . . . • . . . . . • . • . . . . . . . • . .. . •
Location ..•.
Vegetation.
Topography, Slope, and Elevation.
Substrate ..
Disturbance.
ix
1
7
7
7
12
12
13
METHODS AND MATERIALS. . . • • . . . . . . . . . . . . . . . . • . . . . • . . • .
15
RA.N GE • • • • • • • • • • • • • • • • • • • • • " • • • •
23
8
•
•
•
•
•
•
•
•
•
•
•
•
•
&
•
•
•
•
•
•
ESTIMATED TORTOISE DENSITIES. . . . . . . . . . . . . . . • . • . . . . . .
24
HIGH DENSITY AREAS. • • . . . . . . . . . . • • . . . . . . . . . • • . • • . . . . .
28
COMPARISONS OF HABITAT TO ESTIMATED TORTOISE
DENSITIES . . . . . . . . . . . . . . • . . . . . . . • . . . ., .. ., .
37
Vegetation ...•....
Topography, Slope, and Elevation.
Substrate .•.
Disturbance ..
37
43
50
51
DISCUSSION . . . . . . . . . . . • . . . . . . . . . . . " . . . .
e..............
The
Method . . . . . . . . . . . . . . . . .
Comparisons
to Estimated
Tortoise
54
54
o
59
Vegetation ..
Disturbance ..
59
63
The Viability of the Tortoise in Nevada ..•..•..
64
8.......
80
REFERENCES . . . . . . . . . " . . . . . . . . . • . • . . • • • • • . . • . . • .
iv
APPENDIX I.
Estimated Relative Density and
Distribution of Gopherus agassizi
:lil ~~"ClClCl...............................
88
APPENDIX II. Major Shrub Layer Vegetational
Communities in Gopherus agassizi
Study Area in Nevada •..........•.•......
90
APPENDIX III. Transect Data Form .•.•.•...•.....•......
92
APPENDIX IV. Sign Located on Transects •••......••.•..
95
A.
B.
c.
Sign Located on Lincoln County Transects .•.
96
Sign Located on Nye County Transects .......
99
Sign Located on Clark County Trasects ...... 103
vi
LIST OF TABLES
Table
1
2
3
4
5
6
7
8
9
10
11
Tortoise Sign on Multiple Transects at
Study Plots of Previously Determined
Tortoise Densities .•.....•••......•..•.•......
17
Tortoise Densities Estimated from Sign
Observed on Transects .•••.........•.......•...
19
Proportion of Each Estimated Tortoise
Density Class.................................
27
Shrub Layer Communities Compared to
Estimated Tortoise Density, Excluding
Bromus rubens-Dominated Transects .••••......•.
44
Bromus rubens-Dominated Transects Compared
to Estimated Tortoise Density, Excluding
Transects in the Coleogyne ramosissima
Community and Coleogyne ramosissima-Larrea
tridentata Ecotone .•...............••••.......
45
Bromus rubens-Dominated Transects Compared
to Estimated Tortoise Density Excluding
Transects in the Coleogyne ramosissima
community.....................................
46
Comparisons of Estimated Tortoise Density
Classes to Topography and Slope Percentage ....
48
Comparisons of Estimated Tortoise Density
Classes to Elevation .•...••••.....••.•.•.....•
49
Comparison of Individual Disturbances to
Estimated Tortoise Density .•..•..••...••..•...
52
Sign Differences between 1979 and 1981
Transects on the Piute Valley Study Plot ......
57
A Comparison of Sign and Resultant Tortoise
Density Estimates on 13 1981 Transects
(Biosystems Analysis Inc., 1982) Surrounding
Lincoln Transect No. 5 to Sign and Density
Estimates on Transect No. 5...................
60
vii
LIST OF FIGURES
Figure
l
Page
Distribution of Gopherus species in
North Arrlerica . . . . . . . . .
2
a
••••••••
"
.........
"'
•
•
•
•
Transect Sites to Determine Distribution
and Estimated Densities of Gopherus
agassizi in Nevada ...........................
2
8
3
Transect Sign from Multiple Transects on
Six Study Plots, Correlated to Estimated
Tortoise Density on Each Plot ................ 21
4
Shrub Layer Communities Compared to
Estimated Tortoise Density ..•.....•.......... 39
5
Bromus rubens-Predominated Transects
Compared to Estimated Tortoise Density ....... 41
viii
ABSTRACT
THE
DISTRIBUTION,
HABITAT
RELATIVE
ASSOCIATIONS
GOPHERUS
OF
AGASSIZI,
DENSITIES
THE
IN
DESERT
AND
TORTOISE,
NEVADA
by
Alice Elizabeth Karl
Master of Science in Biology
To determine the distribution, relative densities and
habitat associations of Gopherus agassizi in Nevada, a
5500 square mile study area was surveyed using
transects.
3~2
strip
Evidence of tortoises was found to the eastern,
western, and southern boundaries of the state and nearly
as far north as Leith (T8S)
(Tl2S) in Nye County.
in Lincoln County and Beatty
Although other studies have suggest-
ed that tortoises range as far north as Tl2S in Nye County
and T7S in Lincoln County, the vegetation associated with
these northern sites is unlikely to represent tortoise
habitat.
Over 90 percent of the surveyed area (approximately
2
5000 mi )was estimated to have densities less than
2
50 tortoises/mi ; this density has been previously suggested to represent the lower critical level for survival.
ix
Ten areas are estimated to have densities exceeding fifty
2
tortoises/mi : Coyote Springs Valley, Hidden Valley, Dry
Lake Valley, Moapa Valley, the Virgin Mountains, Eldorado
Valley, Piute Valley, Goodsprings Valley, Arden, and Pahrump.
The viability of the tortoise in Nevada is discussed
with respect to population densities, natality rate, mortality rate, amount of available habitable land, and degrees of disturbance.
It is suggested that only the Vir-
gin Mountains, Piute Valley, Eldorado Valley, Moapa Valley,
Coyote Springs Valley, and Hidden Valley populations may be
viable as a result of environmental constraints and current
size.
Evidence of tortoises was found primarily in the Larrea tridentata community (94.7 percent of 171 transects
where tortoise presence was positively identified).
Tor-
toise evidence was also found in the L. tridentata-Coleogyne ramosissima ecotone and the
~·
ramosissima community.
However, there was a significant negative correlation between estimated tortoise density and the dominance of
c.
ramosissima in the shrub layer, probably as a result of
either climatic constraints associated with
or associated Bromus rubens.
c.
ramosissima
A significant negative corre-
lation also existed between estimated tortoise densities
and the domiriance of B. rubens in the understory.
No
evidence of tortoises was found in the Pinus monophylla-Juniperus community.
Tortoise sign was found on slopes with steepnesses up
X
to 60 percent; however, estimated tortoise densities were
lower than expected on mountain slopes, using a
x2 analysis.
Elevations between 1320 and 4560 feet showed evidence of
tortoise habitation; the data were inconclusive in establishing an elevational limit, although 4000 feet is suggested.
Difficulties encountered in employing the transect
method for determining tortoise densities are discussed. It
is determined that the method is appropriate for estimating
regional densities and thereby identifying critical areas
to be more closely investigated during land usage decisions.
xi
INTRODUCTION
The desert tortoise, Gopherus agassizi, is one of only
four species of tortoises (family: Tustudinidae) native to
North America (Conant, 1975) and is endemic to the southwest.
The remaining species, all members of the genus
Gopherus, include G. berlandieri in Texas and Mexico,
flavomarginatus in Mexico, and
Q.
Q. polyphemus in the south-
eastern United States (Figure 1).
Most demographic studies on G. agassizi have been
undertaken within the last decade, with the exception of a
10-year study of a Utah population by Woodbury and Hardy
(1948), initiated in 1936.
In California, Luckenback (1976)
conducted field surveys in 1974 and 1975 to determine the
distribution, relative densities and habitat requirements
of G. agassizi in that state.
Patterson (1976) examined
the historic and current distribution of
Q· agassizi in
California via a search of literature and museum records
and requests for personal sightings.
Between 1975 and 1977
transects were walked by several researchers for the Bureau
of Land Management (B.L.M.) on 1153 sites to determine
relative densities and the distribution of G. agassizi in
California (Berry, 1977, 1978, 1979a; Dimmitt, 1977; St.
Amant, 1979).
The B.L.M. also established 21 permanent
study plots between 1977 and 1979 to examine population
1
2
Figure 1.
Distribution of Gopherus species in
North America (from Carr, 1952).
'
'
3
4
parameters and desert tortoise ecology.
In Utah, Hardy
(1976) re-examined the Beaver Dam Slope population of his
1948 study during the 1960's and Coombs reported on the
status of this population in 1977 (Coombs, 1977a).
Research
in Arizona included a 2-year study on the extension of the
Beaver Dam Slope population into Arizona by Hohman and
Ohmart (1977, 1978, 1979).
The principal objectives were
to determine population parameters, feeding habits, and conflicts with livestock grazing; the B.L.M. continued similar
research on this population for an additional 2 years
(Sheppard, 1980).
Schwartzman and Ohmart (1976, 1977)
initiated similar research on another population, in Pinal
County, Arizona, in 1975 and Schneider examined the ecology
and population structure of 6 additional populations in 1980
while under contract to the B.L.M.
Burge (1979) sampled 289
sites (= 800 miles) to determine the present distribution of
Q· agassizi within designated areas in Arizona.
Arizon~
In 1981 the
Game and Fish Department not only augmented these
findings using intra-departmental questionnaires (Taubert,
1982), but also began field inventories to examine habitat
preferences (Walchuk and Devos, 1982).
In Nevada, Burge
(1977) examined the demographics and ecology of a population
of tortoises near Las Vegas in 1974 and 1975.
Enriquez
(1977) conducted a 4-hour survey on a site in Coyote Springs
Valley, Nevada to determine tortoise densities there and
the Nevada Division of Wildlife Resources briefly surveyed
specific habitats in Nevada in an effort to estimate the
5
northern limits of the desert tortoise in Nevada and key
habitats (Lucas, 1979; Turner, 1980).
Results of the aforementioned studies revealed that
G. agassizi faces potential extinction throughout its
range due to low numbers, fragmented populations, habitat
loss from urbanization, agricultural development, roads,
grazing and Off-Road-Vehicles (O.R.V. 's), and direct impacts
from vandalism.
The Utah population on the Beaver Dam Slope
(where approximately 50 percent of all Utah tortoises are
located) has witnessed an average 7.49 percent annual
decline in its size (although Templeton, 1980, questions
this figure)
as well as a decline in its health (manifested
by an unfavorable sex ratio
(Coombs, 1977a).
and age structure) since 1948
In Arizona, Burge (1979) estimated that at
least 82 percent of the area which she surveyed had densi2
ties less than 50 tortoises/mi ; Berry and Nicholson (1979)
have suggested that this density may be below the minimum
viable population size.
In California, only 2.8 percent of
the desert is suspected to have viable populations (Berry
et al., 1979); annual rates of decline are estimated to fall
between 3.2 and 6.8 percent for the 4 areas proposed as
Critical Habitat and between 1.9 and 17.2 percent for all
California populations examined.
Results from the Nevada
studies were inconclusive regarding the status of G.
agassizi in that state.
Because of these results, G. agassizi is currently
listed as "threatened" in Utah by the federal government and
6
receives state protection in California and Nevada.
Arizona it may still be collected,
killed or exported.
a~though
In
it may not be
Additionally, G. agassizi is catego-
rized as a "sensitive" species in Nevada.
This sensitive
designation is determined by the B.L.M. State Director, in
cooperation with the Director of the State Wildlife Agency.
It insures that the designated species receive special consideration in land usage decisions in order to minimize
the potential for federal or state listing.
Such listing
would legally require increased management and funding to
insure the improval or maintenance of the status of the
listed species.
Consequently, to gain insight into the status of
G. agassizi in Nevada, necessary for the preparation of
Grazing Environmental Statements (G.E.S.) for Clark and
Nye counties, Nevada, and to augment the existing G.E.S.
for Lincoln County, Nevada, the B.L.M. contracted me to
gather data on the distribution, relative densities and
habitat associations of G. agassizi in those counties as
well as data on the demographics of 3 tortoise populations
in Clark and Nye counties (Karl, 1979a,b, 1981).
thesis reports the findings of the former surveys.
This
STUDY AREA
Location:
The surveyed area comprised 153 townships
(Clark County - 104, Lincoln County - 29, Nye County - 28)
south of Sprindale (TlOS) in Nye County and Leith (T8S) in
Lincoln County to the state boundaries, a total of approximately 5500 square miles (Figure 2) .
Vegetation:
In Clark and Nye counties, the Larrea
tridentata - Ambrosia dumosa (creosote bush-bursage)
community is common up to elevations of approximately 4000
feet.
In the higher latitudes of Lincoln County, this
community is found as high as 3600 feet, but is uncommon
above 3300 feet.
Coleogyne ramosissima (blackbush) enters
the shrub layer at about 3000 feet in Lincoln County and
3300 feet in Clark and Nye counties, with the L. tridentata-
c.
ramosissima ecotone extending to about 4000 and 4300
feet, respectively.
The
~-
ramosissima
co~~unity
is the
dominant community above approximately 4000 feet in Clark
and Nye counties and is the major community in several sites
(38 percent) over 3300 feet in Lincoln County.
The result of these elevational limits is that the
L. tridentata-A. dumosa community is the dominant shrub
layer community at most sites
sampled from approximately
Carp (TlOS) in Lincoln County, south through Clark County
(Appendix II).
In Nye County this community or the
7
. d
9
'
I
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I
~--. .
h--r
_ _ _ .,
I
-.~
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L.-----..(
\,,l ______ j
l
,. ;"'r
/ ,
-!;,_ . .,. __ ,)_____
L. ... ..:.
·1
',
J
' . . ,__).
'
I
'
I
/~ '•--~--·-···1•-i
'--..-----
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10
L. tridentata-Atriplex confertifolia (creosote bush-shadscale) community is dominant from the region of Bare Mountain (Tl3S) south.
Associated species in these communities
include Sphaeralcea ambigua, Eurotia lanata, Krameria
parvifolia, Thamnosma montana, Ephedra nevadensis, Opuntia
echinocarpa, Lycium andersonii, Dalea fremontii, Yucca
schidigera, Y. brevifolia, and the perennial grasses,
Oryzopsis hymenoides, Hilaria rigida, Muhlenbergia porteri,
Stipa sp., and Aristida sp.
Perennial grasses are very
common in Kane Springs Valley and north of the Mormon Mts.
in Lincoln County.
Atriplex hymenelytra (desert holly) is
very common in Nye County in southeastern Ash Meadows
(Beatley, 1976) and in Pahrump Valley (Beatley, 1976;
personal observation) .
North of Beatty (Tl2S) in Nye County and Carp in Lincoln County, C. ramosissima becomes the predominant shrub;
northeastern Kane Springs Valley and north-northeast of the
Mormon Mts. is largely ecotonal.
in the
c.
ramosissima community include Y. brevifolia, Y.
schidigera,
tana.
Commonly occurring species
~-
baccata, Opuntia acanthocarpa, and T. mon-
Occasional species are
~·
parvifolia, E. nevadensis,
H. rigida, Aristida sp., and Haplopappus linearifolius.
Juniperus osteosperma, Pinus monophylla, and Quercus
turbinella were resident with C. ramosissima near Gold
Butte (Clark County) .
Difficulty was encountered in assessing the density and
composition of the understory vegetation (herbaceous
11
perennials and annuals less than ca 15 em in height) •
Annual variability in the germination and survival success
of winter annuals occurs in response to annual variation in
rainfall (Beatley, 1966).
However, where the introduced
annual grass, Bromus rubens (foxtail brome), is common or
dominant, it probably retains this relative position in the
community through time (Beatley, 1966).
Its reproductive
success is a result of (a) increased survivorship,
(b)
decreased moisture and possibly temperature requirements
for germination, and (c) probable greater fertility over
native annuals (Beatley, 1976).
In Lincoln County, B.
rubens appeared to be the dominant understory species for
most of the area surveyed, with the exception of Coyote
Springs Valley, the bajadas and rolling hills west of the
southern portion of the Mormon Mts., and the area east of
the East Mormon Mts.
In these areas, the vegetation was
similar to that encountered throughout most of Clark County,
commonly including annual grasses
(~.
rubens, Festuca
octoflora, Schismus arabicus, Bouteloua sp.), the perennial
grass Erinoneuron pulchellum, Plantago insularis (especially
common and often dense on hillsides), Chaenactis spp.,
and Chorizanthe rigida.
Less frequently encountered, but
also common, were borages (Cryptantha spp., Pectocarya
spp.), Eriogonum spp., Euphorbia spp., Pectis papposa,
Amsinckia tessellata, and Erodium circutarium.
Notable
exceptions were the areas from (a) St. Thomas Gap south,
(b) the land west and north of Goodsprings, to route 39,
12
and (c) Eldorado and Piute valleys.
B. rubens was dominant
in the first two areas and A. tessellata was very common,
often with P. papposa and E. cicutarium, in the last.
The understory vegetation in Nye County appeared somewhat different from that in Clark and Lincoln counties.
North of Ash Meadows, C. rigida seemed predominant.
B.
rubens was dominant north of Crater Flat and associated with
~-
insularis, E. pulchellum, and E. cicutarium.
The
remainder of the surveyed area was primarily Chaenactis
spp. and the borages and grasses mentioned above.
Topography, Slope, and Elevation.
Alluvial fans,
bajadas and very gently rolling hills (with slopes less
than approximately 15 percent) were the primary land forms
sampled (74 percent of all transects).
The remainder of
the surveyed sites were equally divided between valleys and
steep hills or mountain slopes (with slopes of approximately
15 to 60 percent) •
The degree of sloping ranged from 0 to
approximately 60 percent, with an average of 7 percent.
Land between 1220 and 4880 feet in elevation was surveyed;
the average elevation was 2775 + 662 feet.
Substrate.
While the soil is friable (primarily soft
to slightly hard consistency), coarse particles, often calcareous, decrease friability in some areas.
Particle size
generally corresponds closely to the topography of the
transect site; i.e., boulder outcrops and dense layers of
gravel are found on the hillsides, cobbles are common in
areas of heavy water drainage, fine gravel is most common
13
on gentle slopes and playas are silty and have coarse
particles.
Alkali flats are present on north-northeastern Crater
Flat, around Pahrump and throughout Ash Meadows.
Disturbance.
Old, seldom-travelled dirt roads, often
little more than barely discernible tracks, were common
throughout the surveyed area.
Cattle grazing was also
common in Lincoln County (at all sites) and Clark County
(50 percent of the sites), although there was little evidence of it in Nye County (only 2 sites in the southeastern
and northwestern regions of the survey).
However, wild
horse and/or burro grazing was common in Nye County (in 43
percent of the transects) .
Equid grazing was only occa-
sionaly present in Lincoln and Clark Counties (13 percent
of all sites).
Evidence of O.R.V. traffic was occasional
in Lincoln and Nye Counties (in 23 percent of all sites) but
relatively common in Clark County (in 43 percent of the
transects).
The extent of O.R.V. use was difficult to
ascertain as dirt roads are probably also utilized.
Only
occasional tracks off roads were observed in most instances;
in only 15 percent of the 111 transects where tracks
(mostly motorcycle) were seen were there many tracks.
How-
ever, in none of these areas could it be determined if (a)
the tracks had been made by a few bikes traversing the area
several times rather than by several bikes, of (b) the use
had been a single occurrence.
havily used "play area."
No area appeared to be a
14
Private land is negligible in Lincoln County, about
6 square miles along Meadow Valley Wash, and in Nye County
it is concentrated in Ash meadows, Pahrump Valley and
Beatty, approximately 150 mi
BLM, 1977).
2
(Figure 2; data obtained from
In Clark County, however, private lands, con-
centrated around Las Vegas and along the Muddy and Virgin
2
rivers, total approximately 500 mi , while state and
federally controlled forests, parks and recreation areas
2
total approximately 1025 mi •
The Desert National Wildlife
Range, the Nevada Test Site and the Nellis Bombing and
Gunnery Range occupy approximately 4400 mi 2
• d
METHODS AND MATERIALS
Three hundred and twelve strip transects were walked
on public lands in Clark (two hundred and three transects),
Lincoln (fifty-two) and Nye (fifty-seven) counties.
The
Clark County transects were performed in Fall, 1979; the
Lincoln and Nye counties' transects were walked in Spring,
1980.
General areas to be surveyed were suggested by the
B.L.M.; the criteria included public lands, below 5000 feet
in elevation.
I selected actual transect sites on the basis
of proximity to adjacent transects (two sites per township
were transected, resulting in a fairly regular intertransect spacing of approximately four miles), avoidance of
habitat lost to agriculture or urbanization, and access.
Additionally, no transect was located with 0.5 mi of any
paved road, with the exception of 4 transects, due to
Nicholson's (1978) finding that there is a significant
decrease in tortoise densities adjacent to roads, up to a
lateral distance of 0.5 mi.
No transect was initiated less
than 0.3 mi from a graded dirt road.
The transect method was developed by Berry et al.
(1979).
Transects were 1.5 mi in length, approximately 10
yds wide and comprised an equilateral triangle.
An effort
was made to sample only homogeneous habitats in order to
minimize errors due to heterogeneity (Berry et al., 1979).
15
16
Transects were 1.5 mi in length, approximately 10 yds wide
and comprised an equilateral triangle.
An effort was made
to minimize errors due to heterogeneity {Berry et al., 19791
However, because a compass heading was followed, this was
occasionally impossible.
All indications {sign) of tor-
toises (e.g., burrows, scats, tortoises, skeletal remains,
tracks, eggs) encountered in the transect were recorded
(Appendix I) •
The amount of tortoise sign encountered during a transect was used to estimate the tortoise density at that
site.
Because of the seasonal and daily variation in tor-
toise activity which coincided with the surveys, two categories of sign were used to estimate tortoise density, as
suggested by Berry et al.
(1979) : burrows and total adjusted
sign (TAS--this terminology was suggested by Biosystems
Analysis Inc., 1982, after Karl, 198lb; it is also referred
to as "adjusted total sign'' in that paper and "corrected
total sign in Berry et al. 1979).
TAS refers to the total
sign minus that sign which occurred with other sign (e.g.,
a tortoise in a burrow is one sign, not two) .
In order to estimate tortoise density from transect
sign, sign levels from each of several transects on five
study plots, four in Nevada (Burge and Bradley, 1976;
Karl, 1979a, b, l98la) and one 15 mi west of the Nevada
border (Karl, 1978) were compared to the previously estimated tortoise densities at each study plot (Table 1) using
a linear regression analysis (Figure 3) .
From the analysisr
17
Table 1.
Tortoise Sign on Multiple Transects at Study
Plots of Previously Determined Tortoise Densities.
IDeation of Study Plot
Estimated
Tortoise
Density
(#/rni 2)
Transect
Number
Tortoise Sign
Burrows
Total
Adjusted
Shadow Valley, CA*
(Karl, 1978)
50
174
173
172
4
6
7
7
6
7
Piute Valley, NV**
(Karl, 1979a)
125
110
111
112
10
4
12-13
11
7
13-14
1
2
3
4
5
6
16-18
12-16
8-9
14-18
13-18
8-ll
17-19
14-18
8-9
16-19
14-19
10-13
197
203
3
2-3
5
2-3
192
193
194
195
196
3-4
4-5
2-3
3-5
10
4-5
6-7
4-5
6-8
19
5
6
1
2
3
4
5
6
2-4
3
0
0
3-4
1
2
0
2-4
6
0
0
4-5
l
3
l
Sheep Mountain, NV**
(Karl, 197 9b)
50
Arden, NV**
Last Chance, NV**
(Karl, 198la)
10
* - Transects walked during employment with California
Department of Fish and Game; November, 1978.
** - Transects in current report.
*** - Transects walked during employment with BioSystems
Analysis, Inc.; August, 1981
+
Burge et al. (1976) estimated a density of 114
2
tortoises/mi . Because of increased urbanization
since that time and the fact that the transects
used for the analysis were adjacent to, not on, 2
the study site, an estimate of 100 tortoises/mi
was used.
18
an index was established in which sign located at each
transect site could be converted to estimated tortoise
density (Table 2).
Similarly, Berry et al.
(1979) employed
a "modified" linear regression, which involved the removal
of four of the more deviant points from the calculation.
Broad categories of estimated tortoise density, with
divisions at 50 tortoises/mi
2
intervals were used rather
than narrower divisions, in accordance with Berry et al.
(1979).
I concur with these broad divisions because of the
inexact nature of collecting and analyzing the data, in the
present project.
Not only was there merely a single tran-
sect per site, resulting in a potentially inaccurate estimate of the tortoise density at each site (note the intertransect variation in the number of sign at all sites in
Table 1) , but the index formulated (Table 2) is based on
estimated, not absolute, densities at the study sites.
A
distinction was made between 0 to 10 and 11 to 50 tortoises/mi2 to delineate areas with potentially no tortoises
and those with tortoises; this division is derived from
the regression analysis.
An additional category of 1 to
10 tortoises/mi 2 was utilized for those transects in which
no sign was found, but near which sign was sighted by me
or reported by B.L.M. personnel.
Disturbances at each site (e.g., roads, grazing, O.R.V.
use, mining, housing) and the dominant flora (i.e., the
prevalent species, estimated by the relative degree of cover
and frequency) were estimated visually.
The shrub layer
Table 2.
Tortoise Densities Estimated from Sign Observed on Transects
Burrows
Total Adjusted Sign
Estimated
2
# Tortoises/Mi
Estimated
# Tortoises/mi 2
# Sign
0
0-10
0
1-4
11-50
1-4
11-50
5-9
51-100
5-9
51-100
10-13
101-150
10-14
101-150
14-18
151-200
15-19
151-200
:;;:19
:;;:201
:;;:20
:;;:201
# Burrows
0-10
I-'
\.0
20
vegetation was mapped from these observations, with supplemental data from the Las Vegas District Office of the
B.L.M., Beatley (1976) and the Nevada Division of Water
Resources (1971).
Soil consistence and texture were
assessed similarly and described in U.S.G.S.
(1961) terms.
No quantitative measurements were collected on these parameters.
However, data on cattle, sheep and domestic horse
grazing from 1967 to 1979 were supplied by the B.L.M., Las
Vegas District.
The geomorphology of each site was des-
cribed and the slope and aspect were computed from appropriate 1:650,000 or 1:25,000 U.S.G.S. topographical maps.
A representative photograph of each site was taken.
To formulate associations between habitat characteristics (other than elevation) and estimated tortoise densities, a chi square contingency table was used.
To deter-
mine associations between elevation and estimated tortoise
density, a Student's t-test was used.
22
X
""
CT>
~
X
0
CT>
+
en
0
....,
U")
6
6
+
...._
~""
0 00
I
II
00
00
I 6
\
II
II
>-
0
II
>(I')
"" E
<
......
.........
....,
Cl>
....,
.........0
...• ....• ...
....
...
0
......
.:
•
0
....
Cl>
..c
E
=
I:
•
; .........
••
•
0
~
>-
f.-
V')
z:
L.I.J
0
L.I.J
V')
0
...•
10:::
0
~
U")
0
""
•
0
""
~
~
...,.
N~IS
!:::
0.
.:10
QO
<.J:)
......•• ...
...
•
...,.
~!38WnN
""
0
f.-
RESULTS
Range
Evidence of tortoises extended to the boundaries of the
survey except the northern; sign was found nearly as far
north as Leith (TBS) in Lincoln County and Beatty in Nye
County (Appendix I).
However, one long-time Beatty resi-
dent reported that tortoises reside in the area of Buck
Springs (Tl2S, R46E).
Although Buck Springs was not sur-
veyed, I question the presence of tortoises there because
of the high elevation, 4600 feet.
Not only is this higher
than any area where tortoise sign was found (see "Results:
Comparisons of Habitat to Estimated Tortoise Densities;
Elevation), but it is an elevation which would be indicative
of a plant community (either Coleogyne ramosissima, Pinus
monophylla-Juniperus osteosperma, or Artemesia tridentata)
above the
~·
tridentata zone (Beatley, 1976).
If the
identification of L. tridentata as the vegetal community
associated with
see "Results:
~·
agassizi is correct (with few exceptions;
Comparisons of Habitat to Estimated Tor-
toise Densities; Vegetation"), then few tortoises, if any,
would be present at Buck Springs.
Similarly, on the basis
of elevation and resultant vegetation, it is possible that
23
24
tortoises are found along the 4000 foot contour, as far
north as Yucca Lake (TllS/12S) in eastern Nye County.
Beatley (1976) reported a continuous L. tridentata community to this latitude and altitude.
Lucas (1980) suggested that tortoises are present as
far north as northern Pahranagat Valley in Lincoln County
(T7S, R44E).
The method used to determine this range limit
was not defined, although Lucas suggested that the vegetation was suitable for tortoise habitation in these localities.
However, according to the Nevada Division of
Water Resources map (1971) and Tidestrom (1925) the vegetational cover is predominantly Salt Desert Shrub (Sarcobatus vermiculatus associations) , Northern Desert Shrub
(Artemesia tridentata associations), or Pinyon-Juniper
Woodland
tions.
(~.
monophylla-~.
osteosperma) , at higher eleva-
Thus, it is likely that the northern limit of
observed sign presented here represents the actual northern
limit of the range of G. agassizi in Nevada.
Estimated Tortoise Densities
To delineate areas within which tortoise densities were
estimated to be uniform, polygons were drawn around singular
transects or groupings of transects with the same estimated
tortoise density, midway to transects of different estimated densities, unless there were major distinctions in
topography or vegetation.
In this case, the polygon line
25
followed the interface between habitat features.
Where no
obvious distinctions occur within each polygon, all tortoise densities within the polygon are assumed to be equal.
Where the transect occurred on the boundary between polygons
of different tortoise densities, the polygon line was drawn
through the center of the transect.
Where an unsurveyed
area lay adjacent to a transect, the polygon line was drawn
approximately two miles from the transect, into the unsurveyed area.
Unsurveyed land above 4000 feet, in known C. ramosissima or
~·
monophylla-~.
osteosperma communities or along
river bottons was assumed to have no tortoises, based on
the result that little evidence of tortoises was found outside the L. tridentata community and that 4000 feet was
identified as the approximate elevational limit to L.
tridentata; it is also assumed that tortoises do not swim.
Similarly, surveyed areas with no sign were speculatively
divided into 0 tortoises/mi
2
and 0-10 tortoises/mi
basis of the vegetational community.
2
on the
Where L. tridentata
was uncommon, tortoise densities were estimated to equal
2
0 tortoises/mi , they were estimated to equal 0-10 tortoises/mi2 in the L. tridentata ecotone or L. tridentata
community.
Eas:t of the Meadow Valley Mountains in Lincoln
2
County, the division between 0 and 0-10 tortoises mi was
made on the basis of the vegetal cover as reported by
B.L.M. personnel.
However, discrepancies in the determi-
nation of the shrub layer between the B.L.M. and this
26
researcher in other locations may signal that this boundary
is erroneous.
Some transects were difficult to include in a specific
density grouping, either because of questionable sign (e.g.
transect number 113 in Clark County had 5 burrows, 3 of
which were questionable, with a resultant TAS of 4 to 7
sign; the density at that site was thus estimated to equal
2
11 - 100 tortoises/mi ) or because the number of TAS indicated a different density than the number of burrow sign
(e.g. transect number 120 in Clark County had 2 to 3
burrows, indicating a
tortoise density of 11-50 tortoises/
2
mi , but 6 to 7 TAS, indicating a density of 50-100 tortoises/mi2, density at the site was finally estimated to
2
equal 11-100 tortoises/mi ).
Nearly half of the surveyed area (2300 to 2590 mi 2 ) was
estimated to have no tortoises or densities less than
2
10 tortoises/mi
(Table 3). If unsurveyed land within the
range but assumed to have no tortoises is included, an
additional 1500 mi 2 (1300 in Clark County and 200 in Lincoln County) is added to this figure.
Within the proposed range, there are an estimated
2
7900 mi of suitable tortoise habitat (i.e., land under
4000 feet or in the
~-
tridentata community and not within
urbanized areas or along river bottoms).
430 mi 2 in Lincoln County, 100 mi
2
Approximately
in Nye County and
1200 mi 2 in Clark County are lost to elevation and vegetation.
In Nye and Clark counties, an additional 70 mi
2
27.
Table 3.
Proportion of Each Estimated Tortoise Density
Class
Number of
Transects
Percentage of
All Transects
116
38.2
2300
41.7
25
8.2
290
5.2
135
44.4
2400
43.5
3
1.0
70
1.3
17
5.6
300
5.4
6
1.9
120
2.2
150
&
&
Total
304
Estimated
2
Tortoises/Mi
0' 0-10*
1-10
11-50**
11-100
51-100***
101-150****
100.0
Estllilated Area Occupied
By Each Density Class
Mi.2
% of Total
&
5520
&
100.0
* - Approximately 75 mi 2 (5 transects) may have densities
2
reaching 50 tortoises/mi •
2
(6 transects) may have densities
**-Approximately 90 mi
2
equalling 100 tortoises/mi .
2
*** -Approximately 30 mi
(2 transects) may have densities
2
as low as 11 tortoises/mi .
2
****-Approximately 15 mi
(1 transect) may reach densities
2
of 200 tortoises/mi •
28
.2
and 500 ml ' respectively, are lost to development.
High
Density
Areas
There are ten areas of densities estimated to exceed
2
50 tortoises/mi : Coyote Springs Valley in Lincoln County
and Hidden Valley, Dry Lake Valley, Moapa Valley, the
Virgin Mountains, Eldorado Valley, Piute Valley, Goodsprings Valley, Arden, and south of the Spring Mountains,
near Pahrump, in Clark County (Appendix I).
Densities
are estimated to reach 150 tortoises/mi 2 in Piute Valley,
Goodsprings Valley, the Virgin Mountains, and at the junetion of Hidden and Dry Lake valleys; in Arden they may
2
reach 200 tortoises/mi .
It is also possible that two areas in Lincoln County,
approximately 15 square miles apiece, southwest (Transect
no. 19) and northwest (Transect no. 15) of the Mormon
Mts. may have tortoise densities slightly greater than
2
50 tortoises/mi , if all questionable sign is tallied.
Higher densities seem more plausible for the area of
Transect no. 15 than for that of Transect no. 19.
former, the vegetation
(~.
In the
tridentata, A. dumosa, Yucca
spp.) is distinctly different from that of the surrounding
transects (C. ramosissima or perennial grasses).
There
29
are no apparent environmental distinctions separating
Transect no. 19 from proximate transects.
(In no instance
did the ten high density areas listed above represent islands of distinctive habitat; however, most had some
apparent distinctions--e.g., vegetation; disturbance-from a few, but not all, of the surrounding transects.)
Similarly, there is a site in Stewart Valley in Nye County
(Transect no. 3), approximately 15 square miles in area,
where tortoise densities may exceed 50 tortoises/mi 2 .
The following is a description of each area positively
identified as harboring populations of densities exceeding
2
50 tortoises/mi :
1)
Coyote Springs Valley--This area comprises
2
approximately 15 mi . There are approximately
250 mi
2
of potentially suitable tortoise habi-
tat (below 4000 ft in unsurveyed sites or where
tortoise sign was found) in the immediate area
(south to Hidden Valley) bordered on the northeast and west by the Delamar Mts., the Meadow
Valley Mts., and the Sheep Range, respectively.
The lower reaches of Pahranagat Valley probably
do not provide appropriate habitat because the
vegetation is Salt Desert Shrub (N.D.W.R.,
1971).
To the south of Coyote Springs Valley,
the area is open into Hidden Valley.
Cattle grazing is the major disturbance in
2
this area, with 1600 A.U.M. 's (~3.5 cattle/rni )
30
grazed throughout the site between January 1
and April 15.
(A.U.M.
=
Animal Unit Month;
this is a grazing unit utilized by the B.L.M. and
is equivalent to 1 cow or horse/month or 5 sheep/
month.)
O.R.V. use is nearly non-existent and
there is no private land.
Impacts from roads
include the two-lane Highway 93 (the main northsouth route in eastern Nevada) , approximately one
mile to the west,
a~d
the graded dirt Kane Springs
road, which experiences little use.
The old
Highway 7, which is in an advanced state of disrepair (i.e., many washouts, revegetated) and
unused, intersects the area.
2)
Hidden Valley--This area of high tortoise density
comprises approximately 50 mi 2 •
It is situated
in a narrow valley, bounded to the west by the
Las Vegas Range and to the east by the Arrow
Canyon Range, both exceeding 4000 ft in elevation.
There are open corridors to the north and south,
providing connections to the Coyote Springs and
Dry Lake valleys populations, respectively. There
2
are approximately 95 mi of potentially suitable
habitat in the valley (to the southern tip of
the Arrow Canyon Range) •
At the northern exit to the valley, density
2
estimates are 1-10 tortoises/mi , increasing
to 11-50 tortoises/mi
2
near Highway 7.
At the
31
southern exit to the valley, density estimates
vary from l-100 tortoises/mi 2 .
Highway 93 intersects this area and there
are a few seldom-used dirt roads and very slight
O.R.V. use.
Cattle are grazed (199 A.U.M. 's
~
l
2
animal/mi ) on approximately 20 mi 2 of this area
in the spring and fall.
3)
Dry Lake Valley--The high density portion of this
area encompasses approximately 30 mi 2 .
The area
is open in all directions to tortoise habitation
although low mountains lie to the south-southeast.
Densities in excess of ll tortoises/mi
2
primarily
surround the high density section; however, transects to the south-southeast showed no sign and
those to the west were estimated to have 1-10
.
I m1.2 .
torto1ses
The major impacts here are from Interstate
Highway 15, which bisects the area, and dirt bike
use.
The Las Vegas Mint 400 race begins here and
I observed a swath of tracks approximately 40
yards wide.
Cattle and some horses are grazed
throughout the area (107-207 A.U.M. 's
~
l animal/
mi 2 ), primarily in the spring, although about
15 mi
4)
2
are also grazed in the fall.
Moapa Valley--This high density area comprises
about 50 mi
2
and is surrounded by populations
2
estimated to have ll-50 tortoises/mi • The
32
approximately 350 mi
2
of habitable land is
primarily limited to northerly directions,
although the Mormon Mts. are probably uninhabited by tortoises because of their elevation
(primarily over 5000 ft) and consequent vegetation (Pinyon-Juniper Woodland).
The Virgin
and Muddy rivers, agricultural development and
urbanization along these rivers, and Interstate
Highway 15 probably effectively block any connection between this population and high density
populations to the south.
Highway 7, two graded dirt roads, and a
railroad (adjacent to one of the dirt roads)
traverse this area.
observed.
Only slight O.R.V. use was
Approximately 80 percent of the area
is grazed by cattle and some horses in the
spring (107-779 A.U.M.'s < 1-3 animals/mi 2 ;
the higher figures apply to 60 percent of the
area) .
5)
The Virgin Mountains--This high density section
2
comprises approximately 70 mi .
It is isolated
from the north and west by the Virgin River and
Lake Mead, respectively, and land is lost to
agricultural development along the shores of
these bodies of water.
To the south, a block
of 10 transects had no evidence of tortoise
habitation, which may be due to the mountainous
33
terrain and elevation over 4000 ft.
The Colorado
River lies south of these mountains.
Available
tortoise habitat in the Nevada portion of the
.
. Mts. area approx1mates
'
200 m1' 2 .
V1rg1n
However,
open land is available to the east, in Arizona,
where an additional 250 mi
2
of potentially suita-
ble tortoise habitat is available.
The majority of the surrounding populations
(with the exception of the area to the south)
are estimated to have 11-50 tortoises/mi 2 .
Hohman and Ohmart (1979) estimate that the proximate population in Arizona has from 40 to 50
I m1.2 .
.
tor t o1ses
The major impact is a 100 percent overlap
in grazing; 70 percent of the area is grazed
2
by 1397-2730 A.U.M.'s of cattle (.:: 1 animal/mi )
in the spring, summer, and fall.
The remainder
is grazed in the spring and fall by 317 cattle
and horse A.U.M.'s (.:: 1 animal/mi 2 ) and 428 sheep
2
A.U.M.'s {.:: 2 sheep/mi ).
Only one very lightly
travelled dirt road (paved in part) supplies
access to this area from Arizona or Riverside.
O.R.V. use was rarely observed and slight.
6)
Eldorado Valley--One transect (influencing
2
approximately 15 mi ) was estimated to have
50-100 tortoises/mi 2 . Most surrounding popula2
tions are estimated to have 11-50 tortoises/mi ,
34
although several transects are estimated to have
2
1-10 or 0-10 tortoises/mi •
Potentially suitable
tortoise habitat extends north to Boulder City,
west to the Eldorado Mts. and east to the
McCullough Range.
An open corridor extends
south to the Piute Valley population.
South to
Searchlight, there are approximately 350 mi
2
of
tortoise habitat.
Highway 95 bisects the area and there is
a large transmission line with an accompanying
access road.
Cattle are grazed on a yearlong
basis (1849-2947 A.U.M.'s ~ 1 cow/mi 2 ); sheep
grazing began in 1980.
Only slight O.R.V. use
was observed.
7)
Piute Valley--This is the largest high density
2
area observed, encompassing approximately 135 mi .
It is bordered to the southeast, west and northwest by areas estimated to contain 11-100 tort
.
o~ses
I m~.2 •
To the east the territory was
unsurveyed, but it is mountainous in the southern
portion (although i t generally remains below
4000 feet in elevation) , thus probably providing
little suitable tortoise habitat; in the northern
portion of the unsurveyed area, the terrain is
gentle and high densities may extend east to
the Colorado River.
To the south, into
Cali-
fornia, density estimates range from 20 to 200
35
tortoises/mi2 (Berry et al., 1979).
Topographically, the limits to tortoise habitat in the valley include the McCullough Range and
New York Mountains to the west and the Newberry
Mts. and Colorado River to the east.
There are
approximately 325 mi2 of potentially suitable
tortoise habitat in the valley.
With the exception of Arden, this area has
the greatest relative human-related impacts of all
of the high density areas.
Highways 95 and 68
intersect it and most applications to the B.L.M.
for motorcycle race permits are requested for
this area.
(Although I observed few tracks,
washes are often utilized by motorcyclists;
B.L.M., personal communication.)
Additionally,
three major power line corridors cross the area.
Grazing occurs year-long and ranges from approximately 1 cow/mi2 (1849 A.U.M. 's) in 30 percent
of the area, to 3 cattle/mi2 (5986 A.U.M. 's) in
30 percent and 4 cattle and 1 sheep/mi2 (1200
cattle A.D.M. 's and 1209 sheep A.U.M. 's) in 40
percent.
Private land comprises approximately
two percent of the area.
8)
Goodsprings Valley--This area, approximately
15 mi2, is very isolated by mountainous terrain
over 4000 ft. to the south, north, and west and
Interstate Highway 15 to the east.
It is slightly
36
open to the northeast toward the Arden area.
North to the southern tip of the Bird Spring
Range, there are about 70 mi
toise habitat.
2
of potential tor-
Surrounding density estimates
range from 0 to l-10 tortoises/mi 2 .
In addition to Interstate Highway 15, disturbance includes the paved Goodsprings Road and
cattle grazing.
The current grazing allotment
permits l animal/mi
2
(174 A.U.M. 's) on a year-
long basis; however, there has been no grazing
since 1975.
9)
No O.R.V. use was observed.
Arden--The high density transects occupy approxi2
mately 50-75 mi .
This area is open only to the
south, where transects indicated ll-50 tortoises/
2
mi .
It is bounded on the west by mountainous
terrain over 4000 ft and on the east by expanding
urban development from Las Vegas.
Twenty-five
percent of this high density area is currently
under private ownership.
Aside from the encom-
passing urbanization, this area is heavily impacted by dirt trails and roads and O.R.V. use.
No grazing occurs in the area.
To the southern end of the Bird Springs
Range there are potentially 160 mi 2 of suitable
tortoise habitat (excluding private land,although
i t does not preclude tortoise habitation).
37
10)
Pahrump--This area comprises approximately 15 mi 2.
Transects to the east and southeast resulted in
2
density estimates of 11-50 tortoises mi ; 1 transect due south indicated 0-10 tortoises mi 2 .
Transects were not walked to the west or northwest, in Pahrump Valley, because of the large
2
area of private land there ( 125 mi ).
The
Spring Mts., which lie directly north and surround the valley to the east and southeast, preeluded transecting land north of the site.
Within the valley and excluding private land,
there are approximately 240 mi
2
of potentially
suitable tortoise habitat.
Highway 16, the main route from Las Vegas
to Pahrump, traverses this area.
Additionally,
cattle are grazed throughout this area during
the spring, summer, and fall (1251 A.U.M. 's,
2
animal/mi ).
No evidence of O.R.V. use was
observed.
Comparisons of Habitat to Estimated
Tortoise Densities
Vegetation.
Tortoise sign was found primarily in the
L. tridentata community (94.7 percent of the 171 sites
where definite tortoise sign was located on or near the
transect); however, evidence of tortoises was also found
in the L. tridentata-C. ramosissima ecotone (4.7 percent)
1
38.
and in the
c.
ramosissima community (0.6 percent).
A significant difference exists between estimated tortoise density categories relative to shrub layer vegetation
type (x 2 =24.44; p < 0.005); estimated tortoise density is
negatively correlated with the dominance of C. ramosissima
(Figure 4).
No
c.
ramosissima-dominated and only 3
f·
ramosissima-L. tridentata ecotonal communities occurred
where tortoise densities were estimated to exceed 10 tor-
I ml.2 •
.
t OlSeS
There was a significant difference (x 2 =33.05; p <
0.005) between the estimated tortoise density categories
concerning the relative number of transects with dominant
B. rubens in the understory.
Where B. rubens was dominant,
estimated tortoise densities were less
(Figure 5).
(B.
rubens-dominated transects were those where few other
under-story species were obvious but commonly included
~·
cicutarium, Astragalus sp. and Lotus sp. in Lincoln
County
and~·
pulchellum in Clark County.
Additionally,
the cover often appeared to be dense.)
Beatley (1966) reported that
~·
rubens,
often the
dominant annual in C. ramosissima communities, is a member
of many
~·
tridentata-C. ramosissima ecotones, and occurs
with unpredictability in the
~·
tridentata community.
In
view of this, the possibility arises that the common
occurrence of B. rubens in transects where
c.
ramosissima
was dominant might be the reason for the negative correlation of C. ramosissima with estimated tortoise densities.
39
Figure 4.
Shrub layer communities compared to estimated
tortoise density.
L =Larrea tridentata·and
Coleogyne ramosissima ecotone; C = C. ramosissima.
!) -expected value; (! 1 ?) =
observed value; clear area = total number of
transects for tortoise density category.
T:
40
130
120
100
90
80
UJ
1-
70
(.)
UJ
UJ
z so
<
a:
1LL.
0
a:
UJ
Ill
50
40
::!:
:::>
z
30
20
10
0
0-10
L L,.C C
. L Lit C
L L/C C
L L/C C
1-10
11-50
51-100
101-150
NUMBER OF TORTOISES
PER
MILE
2
41
Figure 5.
Bromus rubens-predominated transects compared to estimated tortoise density.
( : : ) = expected values; ( ',~,, ) =
observed values; clear area = total number
of transects for tortoise density category;
A = Predominant B. rubens; B = B. rubens
is not predominant.
42
100
90
80
70
..... 60
V>
u
u.J
V>
z:
c:(
50'
w...
40
a::
.....
0
0::
u.J
CQ
2
30
::;:)
z:
20
!G
0
0-10
NUMBER
1-10
11-50
OF 10RTOISES PER MILE 2
51-100
I 01-150
43
In fact, 50 percent of the
~·
ramosissima transects and
60 percent of the C. ramosissima-L. tridentata ecotonal
transects had B. rubens-dominated understories.
When tran-
sects with dominant B. rubens was removed from the
x2
calcu-
lation, no significant difference between the shrub layer
vegetation and estimated tortoise densities existed (x 2 =
16.8; 0.10 < p < 0.05); i.e. the presence
of~·
ramosissima
was no longer correlated with estimated tortoise density
(Table 4) .
Consistent with this, it is possible that the reason
for the negative correlation between the dominance of B.
rubens and estimated tortoise densities might be due to the
presence of
c.
transects.
However, 66 percent of the transects where
ramosissima in most B. rubens-dominated
B. rubens was dominant occurred in the L. tridentata
community.
or
c.
And, when all transects in the C. ramosissima
ramosissima-L. tridentata ecotone were deleted from
calculations, a significant difference (x 2 -25.1; p < 0.005)
remained between transects with dominant B. rubens and
estimated tortoise densities
(Table 5).
Similarly, when
only transects in the C. ramosissima community were excluded,
the difference remained significant (x 2 =29.82; p < 0.005;
Table 6).
Topography, Slope, and Elevation.
sity
classes
All estimated den-
were found in valleys (canyons were included
in this group) and on bajadas, rolling hills, mesas and
steep hills.
However, only one transect with an estimated
Table 4.
Shrub Layer Communities Compared to Estimated Tortoise Density, Excluding
Bromus rubens-Dominated Transects.
Estimated
Tortoise Densit¥
(# tortoises/mi )
Shrub Layer Community
Coleogyne
ramosissima
Ecotone
Observed Expected
Observed Expected
Larrea
tridentata
L:
Observed Expected
0' 0-10
6
2.2
5
2.8
65
71
76
1-10
0
0.5
0
0.7
18
16.8
18
11-50
0
2.8
3
3.8
98
94.4
101
51-100
0
0.4
0
0.5
14
13.1
14
101-150
0
0.1
0
0.2
5
4.7
--
5
L:
6
6.0
8
8.0
200
200.0
214
x2
=
14.53; P > o.o5; d.f.
=
8
.!::>
.!::>
Table 5.
Bromus rubens-Dominated Transects Compared to Estimated Tortoise Density,
Excluding Transects in the Coleogyne ramosissima Community and Coleogyne
ramosissima-Larrea tridentata Ecotone.
Estimated
Tortoise Densit¥
(# tortoises/mi )
Transects with
Dominant
Bromus rubens
Transects Without
Dominant
Bromus rubens
l:
Observed
Expected
Observed
Expected
25
12.2
36
48.8
61
2
4.0
18
16.0
20
11-50
11
19.0
84
76.0
95
51-100
1
2.8
13
11.2
14
101-150
0
1.0
5
4.0
0, 0-10
1-10
-39
l:
x2 =
25.1; p < 0.005;
d. f.
=
39.0
156
156.0
5
195
4.
~
Ul
Table 6.
Bromus rubens-Dominated Transects Compared to Estimated Tortoise Density,
Excluding Transects in the Coleogyne ramosissima Community.
Estimated Tortoise
Density
2
(# tortoises/mi )
Transects With
Dominant
Bromus rubens
Transects Without
Dominant
Bromus rubens
L.;
Observed
Expected
Observed
Expected
33
17.6
41
56.4
74
6
5.7
18
18.3
24
11
23.2
87
74.8
98
51-100
1
3.3
13
10.7
14
101-151
0
1.2
5
3.8
5
51
51.0
164
164.0
215
0,0-10
1-10
11-50
L.;
x2 =
29.82; p < o.oo5; d.f.
=
4
~
0'\
47
density greater greater than 50 tortoises/mi 2 occurred on a
mountain slope.
Most transects (24) which traversed moun-
tain slopes indicated that tortoise densities were 0-10
2
tortoises/mi .
This is significantly higher (x 2 =22.4; p <
0.005) than the expected value (15).
Similarly, the number
of transects on mountain slopes indicating 11-50 tortoises/
mi 2 was lower than the expected value (14).
Slopes having a steepness up to approximately 60 percent (mean
tation.
~
4 percent) showed evidence of tortoise habi-
Because of the imprecise method of measuring the
slopes, no quantitative analysis was utilized to compare
steepness of slope to estimated tortoise density.
However,
mean slope percentages were similar among areas having similar tortoise densities (Table 7).
sities greater than 50 tortoises/mi
Areas with estimated den2
had a maximum slope of
12 percent; however, this may be a function of small sample
size for transects with steep slopes (n=35).
Evidence of tortoises was found in areas with elevations between 1320 and 4560 feet, with a mean of 2685 + 583
feet (only 3 sightings of tortoise sign occurred over 3800
feet).
A significant difference (t=4.41; p < 0.001) exists
between elevations of transects with no sign and those with
sign (Table 8).
However, there is no significant difference
in the mean elevation between either transects estimated to
have from 1-10 tortoises/mi
2
and those with > 100 tortoises/
mi 2 (t=l.63; p > 0.05) or between transects estimated to
have from 1-10 tortoises/mi 2 and those with 11-50 tortoises/
Table 7.
Comparisons of Estimated Tortoise Density Classes to Topography and Slope
Percentage
Estimated
'l'ortoise Densi t¥
(# tortoises/mi )
n
Valleys (V)
27
Bajadas, Rolling
201
Hills (B I RH)
Mountain Slopes {M) 35
n
0, 0-10
1-10
11-50
-
% of transects
VITi th this
morphology
112
V-11
B,RH-75
M-24
40.7
37.3
68.6
6
(1-60)
26
V-0
B,RH-24
M-1
o.o
11.9
2.9
4
(0-60)
111
44.4
43.3
25.7
8
(1-50)
V-2
B,RH-12
M-1
7.4
6.0
2.9
3
(0-12)
V-2
B,RH-3
M-0
7.4
1.5
0.0
2
( 0-3)
V-12
B,RH-87
M-9
51-100
101-150
Mean Slope
Percentage
(Range)
15
5
~
co
....
Table 8.
Comparisons of Estimated Tortoise Density Classes to Elevation.
2
Estimated Tortoise Density (#tortoises/mi )
Mean Elevation (ft)
Standard Deviation
Range
N
(ft)
0-10
1-10
11-50
3033
2819
2640
2699
2506
706
640
596
432
321
1320-4040
1800-3280
2200-3050
1500-4880
115
1640-4560
25
112
51-100
15
101-109
5
of;>.
!;0
50
mi
2
( t== 1. 6 0 3 ; p > 0 . 0 5 ) •
The present study does not establish an elevational
limit for the presence of tortoises.
However, two factors
might set the limit at approximately 5000 feet (with
occasional exceptions).
First, estimated tortoise densi-
ties decrease with a decrease in the dominance of L. tridentata, and the upper elevational limit of the L. tridentata community coincides approximately with the 4000 foot
contour.
Second, tortoise sign was only found in 2 of the
16 transects at or over 4000 ft (neither of which were in
the~·
tridentata community).
Substrate.
Evidence of tortoises was found on loose
to hard soils, which were slightly to densely gravelly;
cobbles and boulders were also present in 19 and 22 transects, respectively, where sign was observed.
Because the friability of soil on upper bajadal
slopes is decidedly less than that on lower slopes and in
valleys due to the increased concentration of gravel and
cobbles, it would seem reasonable that tortoise densities
might decrease there because of the difficulty of digging
burrows.
In fact, where tortoise densities were estimated
to exceed 50 tortoises/mi
2
the soil was considered in all
cases to be moderately friable, even considering coarse
fragments
(fine or coarse gravel in all cases).
Similarly,
in a comparison of transects which I walked on upper and
lower bajadal slopes in 1981 in Coyote Springs Valley,
Lincoln County (Biosystems Analysis Inc., unpublished data,
51
1981), 13 and 10 transects respectively, lower slopes had
significantly more burrow signs than upper slopes
(t=l.82; 0.025 < p < 0.05).
The difference in TAS was not
significant, however (t=l.59; 0.10 >
p
> 0.05).
One can only speculate that soil type is important to
tortoises, because assessments of substrate consistency
were too imprecise to be compared quantitatively to estimated tortoise densities.
Disturbance.
Individual disturbances which were each
present in more than ten transects were compared to the
estimated tortoise density classes (Table 9).
Only seldom-
used dirt roads exhibited a significant difference between
the density classes (x 2 =11.67; 0.01 < p < 0.05).
However,
the proportion of observed to expected transects did not
show a consistently negative correlation with estimated
tortoise densities.
In the 0 tortoises/mi
2
class, there
were more transects which were traversed by old roads
(82)
than were expected (73), but this was also true for transects where density estimates were > 50 tortoises/mi 2
(observed = 17; expected = 13).
Thus, there was no apparent
correlation between the number of old roads and estimated
tortoise densities.
In the 17 transects where several motorcycle tracks
were present in each (including 2 transects where there was
a swath of tracks approximately 40 yards wide, probably
indicating a racecourse), estimated tortoise densities
ranged from 0-50 tortoises/mi
2
(1 transect was estimated
Table 9.
Comparison of Individual Disturbances to Estimated Tortoise Density.
Estimated
Tortoise Densi~
(# tortoises/rni )
Cattle
Grazing
n=l56
Horse/Burro
Grazing
n=48
Indivill.dual Disturbances
Paved
O.R.V.
Old Dirt
Roads
Use
Roads
n=27
n=86
n=l76
Graded Dirt
Roads
n=34
0,0-10
69
22
33
82
10
14
1-10
17
2
6
14
2
2
11-50
61
23
39
63
12
15
51-100
8
1
7
13
3
2
101-150
2
0
1
4
0
1
x2
Probability
2.69
5.05
3.54
p > 0.05
p > 0.05
p > 0.05
11.67
2.57
0.01< p< 0.05 p > 0. 05
0.91
p > 0. 05
U1
N
53
2
to have 11-100 tortoises/mi ).
DISCUSSION
The Transect Method
Berry et al.
(1979) described the use of transects as
a good method for determining distribution and relative
densities of tortoises throughout the desert.
However, the
validity of this method has been questioned (Biosystems
Analysis Inc., 1981, in Biosystems Analysis Inc., 1982).
Clearly, no absolute figures can be derived from this
method.
It is merely a rough estimate, based on the rela-
tive abundance of sign located.
Additionally, the index
formulated to correlate sign on transects with tortoise
density was based on estimated, not absolute, densities
on study plots.
(n
=
The low number of transects per site
one) does not allow either for observer error or for
clumped distributions of tortoises and their sign.
The
latter has been observed on several one square mile study
plots (Karl, 1978, 1979a,b,c, 1980a).
In addition, with
only two transects per township (= one transect approximately every four miles), tortoise densities between transects could vary from those estimated by the polygon technique.
Thus, while no absolutes can be claimed using this
method a regional estimate can be obtained (Biosystems
Analysis Inc., 1982, agrees with this perspective).
54
This
55.
is useful to land use agencies because it indicates
potentially critical habitat for the desert tortoise,
which subsequently can be more closely surveyed to determine impacts and necessary mitigation measures resulting
from other land uses.
A case in point is the proposed
site for the MX Missle Base in Coyote Springs Valley.
Because Coyote Springs Valley was identified as a high
density area (this paper, the results of which were presented in earlier reports to the B.L.M.: Karl, 1980b,
198lb), transects were walked at a density of 1 transect
per section (=1 transect/mi 2 or 36 transects/township)
to accurately outline tortoise densities and distribution
in the valley.
Seasonally, fewer scats, tracks, and tortoises are seen
during non-activity periods.
Scats often dissolve after
rain or become increasingly difficult to see as they dry,
changing color from black to pale brown.
Tracks are
ephemeral; however, most sightings of tracks were associated
with burrows, so TAS would not be significantly altered on a
seasonal basis.
No transects were walked on the same site
during activity and non-activity seasons, so the potential
error which might be attributed to seasonal changes in TAS
remains uninvestigated.
The number of burrows per transect, rather than TAS
probably remains the best indicator of tortoise density.
New burrows are dug each spring and probably during the
fall activity period and attrition may occur from flooding,
56
caving-in, or excavation by predators.
However, attrition
rates are probably low and thus the number of burrows
would probably change little between consecutive seasons.
However, on a yearly basis, there might be a continual
increase in the number of burrows if attrition rates are
less than those of construction.
The only site where this
could be tested by this author was the Piute Valley study
plot (Karl, 1979a), where 3 transects were walked in
October, 1979 and 6 were walked in August, 1981.
toises were active during both surveys.)
(Tor-
Using a Student's
t-test, no significant difference was observed in the mean
number of burrows per transect between the concensus
(Table 10) .
The most significant difference occurred with
scats (t=2.632; p < 0.05); there were fewer perDtransect
in the 1981 survey, which may have been a reflection of
forage condition or tortoise activity (Burge, 1980).
systems Analysis Inc.
Bio-
(1982) similarly compared the TAS of
transects on 5 additional sites from 1980 and 1981 (both
sets of transects were walked by this author; data from
1980 are presented in this paper).
A Spearman's r
s
analysis indicated a high correlation between transect
results from different years, on the same site.
Certain features of the substratum and/or topography
may conceal or concentrate sign, resulting in under- or
over-estimations of tortoise densities.
Burge (1979)
observed during transects on mountainsides in Arizona
that scats were concentrated on paths that she and the
Table 10.
Sign Differences Between 1979 and 1981 Transects on the Piute Valley Study
Plot.
Transect Sign
Year
1979
1981
+
++
Skeletal
Remains
Tracks
TAS
Transect
Burrows
Scats
1
2
3
4
10
12-13
3
2
2
0
1
4
0
0
0
0
2
2
X
-
8.8±4.4
2.3±0.6
1.7±2.1
---
l . 3±1. 2
1
2
3
4
5
6
16-18
12-16
8-9
14-18
13-18
8-11
1
1
0
2
0
2
1
1
0
1
3
0
0
0
0
0
0
0
0
1
1
1
0
0
X
13.4±3.6
1.0±0.8
1.3±1.4
---
0.5±0.6
14.6±3.7
1.57
p > 0. 05
2.63
p < 0. 05
0.299
p > 0. 05
-----
1.11
p > 0. 05
1.69
p > 0. 05
Significance
Between 1979
and 1981 Means
(d.f.=7)
t
p
'Ibrtoises
7
11
13-14
10.5±3.3
17-19
14-18
8-9
15-19
14-10
10-13
+ = 28.5% in 1979 and 16.7% in 1981 were associated with burrows.
++ = 100% in 1979 and 66.7% in 1981 were associated with burrows.
+++ = All tracks associated with burrows.
U1
-...]
58
tortoises were forced to use because of the bouldery nature
of the habitat.
Although I was never in this situation, I
did feel that my concentration was decreased on gravelly
and/or steep hillsides, where walking was difficult.
The
width of the transect consequently was decreased here and
also in bouldery and cobbly areas where my visual range
was limited.
Thus, sign may have gone unobserved and tor-
toise densities subsequently underestimated.
Similarly, I
may have underestimated tortoise densities in rocky areas
or areas with caliche washes.
Rock dens are utilized as
coversites (Burge, 1979; Coombs, 1977a; and personal
observation) and several investigators have reported that
tortoises use caliche caves for burrows (Coombs, 1977b;
Woodburn and Hardy, 1948; and personal observation).
How-
ever, unless there was additional evidence of tortoises
associated with the rock or caliche cave, I did not include
it in my sign count.
Additionally, I did not remain in
caliche washes unless they followed my compass bearing.
So, if caliche washes provided a localized source of
coversites for a population of tortoises, I would have
underestimated the density of tortoises by not remaining in
the washes.
As a final potential error in estimating tortoise
density, the number of skeletal remains might actually be
more representative of the mortality rate and previous
tortoise density, rather than current density.
An initial
over-estimation of the population size of tortoises at the
59
Last Chance (Nye County) study plot (Karl, 198la) according
to the results of March trasects, 11-50 tortoises/mi 2 , was
probably due in large part to the number of skeletal remains
found (2 skeletons), as well as to clumped distribution of
sign.
During a concentrated search of the site in May, only
2
10 tortoises were found in 1.5 mi and an estimate of 5-10
2
tortoises/mi was calculated.
In the final analysis, transects do yield an accurate
approximation of tortoise density.
Berry et al.
(in pre-
paration, from Biosystems Analysis Inc., 1982) observed
that tortoise densities determined from 60-day census on
study plots in California were similar to those estimated
from prior transects.
Similarly, the results of the
13 1981 transects by this author {Biosystems Analysis Inc.,
1982) located within a 2 mile radius of Lincoln County
transect no. 5 (that radius approximating the limit of the
polygon drawn around transect no. 5) were within the range
estimated for transect no. 5.
The latter was estimated to
2
have 51-100 tortoises/mi ; mean burrow sign and TAS for
the remaining 13 transects indicated that the tortoisedensity was probably near 50 tortoises/mi
2
and possibly up
?
to 150 tortoises/mi- in the area (Table 11) .
Comparisons of Habitat to Estimated
Tortoise Densities
Vegetation.
The result that estimated tortoise den-
sities decrease with the addition of C. ramosissima as a
60
Table ll.
Transect
Number
A Comparison of Sign and Resultant Tortoise
Density Estimates on 13 1981 Transects
(Biosystems Analysis Inc., 1982) Surrounding
Lincoln Transect No. 5 to Sign and Density
Estimates on Transect No. 5.
Burrow
Sign
TAS
Estimated Tortoise
Density
(# Tortoises/mi 2 )
2
ll-50
6
2
2
5
ll-50(-100)
7
3
5
ll-50(-100)
2-5
3-5
ll-50(-100)
9-12
9-12
51-150
4
lll
9
71
3
5
ll-50(-100)
72
3-5
3-5
ll-50(-100)
141
4
4
139
58
3-5
5-8
3-5
5-8
51-100
138
l-2
2-3
ll-50
69
140
7-8
0-l
10-ll
0-l
51-150
0-50
X
4.1
5
51-100
Lincoln
Co. # 5
4-5
4-5
51-100
ll-50
ll-50(-100)
61
major component of the shrub layer is probably a function
of the climatic constraints imposed with this species.
Beatley (1976) stated that the climatic difference between
the L. tridentata and
c.
amount of precipitation.
ramosissima communities is the
C. ramosissima enters the L.
tridentata community where the mean annual rainfall reaches
6.4 inches and L. tridentata is absent at annual precipitation levels greater than 7.2 inches.
Munz (1959) and
Tidestrom (1925) both stated that the climatic difference
between these communities is that of lower temperatures in
the
c.
ramosissima community (a minimum of -5.5°C and 130
frost-free days as opposed to a minimum of -l.l°C and 190
frost-free days in L. tridentata) as well as increased
rainfall (up to 15 inches in
c.
ramosissima as opposed to
a maximum of 8-10 inches in L. tridentata) .
Because I
observed C. ramosissima as low as 2880 feet, but only on
north-facing slopes at this low elevation, it follows that
temperature, not precipitation, is the major climatic
feature governing the distribution of this species.
One might theorize that the increased precipitation
and/or lowered temperatures coincident with the C.
ramosissima community has a direct, adverse effect on
Q· agassizi, resulting in reduced densities in this
community.
However, it is also possible that the compo-
sition and/or amount of cover of the vegetation associated
with the C. ramosissima community is less favorable for
tortoises than that of the L. tridentata community.
62
Although neither hypothesis was proven to be true when the
transects with predominant Bromus rubens were removed from
the analysis, the sample size of the remaining transects
may be too small to generate any conclusions regarding
C. ramosissima and its effects on
Soil and Vegetation.
~·
agassizi.
Although major shrub communities
indicate the presence of tortoises as a result of climatic
associations, edaphic conditions may impose a greater
influence on relative tortoise densities than vegetation
because of the potential for burrowing.
Varied vegetational
composition within a community undoubtedly reflects the
physical and chemical properties of the soil as well as
local climate and topography.
This was superficially
observed during the present study: e.g., Hilaria rigida
was often a major shrub layer species where soils were
loose and sandy; shrub layer diversity seemed to increase
on upper bajadal slopes, where the soil was cobbly and
densely gravelly; no L. tridentata grew on gypsic soils.
Unfortunately, no quantitative measurements were taken;
however, it would be an interesting future project to
first compare soils to tortoise densities and next, to
outline vegetational subcommunities associated with
different soil characteristics.
The result might enable
an investigator to more accurately estimate relative tortoise densities in an unsurveyed area by using vegetational
indicator species (which constitute a more easily assessed
parameter than soil quality), as well as local abiotic
'
;
63
conditions.
Disturbance.
Results on the effects of individual
disturbances on tortoise densities are insufficient to
generate sound conclusions for several reasons.
First,
there are no data available on previous tortoise densities
against which to compare current findings.
Second, the
methods of gathering the data on both tortoises and disturbance are incomplete and imprecise.
Last, a major flaw
resides in reporting only the presence of a particular
disturbance, and not the current and historical levels
of disturbance, at each site.
To determine the impacts
of disturbance, it would be necessary to know the following
for each:
1)
2
Cattle grazing--the number of head/mi , range
condition (i.e., biomass of forage species),
season of use, history of use
2)
Equid grazing--the number of bands and sizes of
each, use patterns (i.e., migratory patterns),
history of use
3)
Graded or seldom-used dirt roads--the number
of cars/day, both currently and historically,
tortoise densities at successive intervals from
the roads, as per Nicholson (1978)
4)
O.R.V. use--the number and type of permits
issued, the degree of use on old roads and in
washes, seasons of use
64'
This report does not attempt to explore each disturbance to the levels described; the investigation of each
alone would comprise a major project.
The Viability of the Tortoise in Nevada
The viability of a tortoise population is dependent
upon several factors:
1)
Population density--Berry et al.
(1979) suggested
that populations with less than 50 tortoises/mi
2
and possibly up to 100 tortoises/mi 2 may be unable
to survive without adjacent high density popula2
tions (with~ 200 tortoises/mi ) because of the
potentially low number of reproductively active
females.
Proximate high density populations would
serve as "nurseries," supplying the surrounding
lower density populations with young tortoises.
2)
Natality rate (i.e., the percentage of live
hatchlings)--This would depend on the number and
fecundity of the reproductively active females,
the availability of forage, weather conditions,
and nest predation.
Several researchers have indicated that most
reptilian populations have adult sex ratios
nearing 1:1, however, females may outnumber
males four to one, in some species (Tinkle,
1961).
Tinkle (1967) quoted a 55:45 sex ratio,
65
in favor of females, in Uta stansburiana.
Swing-
land and Lessells (1979) observed that there was
a slight differential mortality in males,
resulting in an adult sex ratio in Geochelone
gigantea Schweigger of 1 male:l.6 females.
Berry
(1976) estimated that healthy populations of
Gopherus agassizi do not have a predominance of
males.
However, in one population of
~·
agassizi
which I studied (Karl, 1980a) the sex ratio was
0.55 - 0.61 females: 1 male.
However, the pro-
portion of the population comprising "very young"
tortoises (those under 100 mrn in carapace length)
was 24.6%.
Berry et al.
(1979) suggested that in
a healthy population of tortoises, this very young
age class usually comprises only 5-15% of the
population.
Several factors may have contributed
to the apparently high reproduction in this population, despite the sex ratio.
Optimal environ-
mental conditions (e.g., coversite potential,
forage availability and quality) may have reduced
mortality and/or increased reproduction.
The
quantity and timing of rainfall is of primary
importance to the production of forage, which
has, in turn, been positively correlated to reproduction rates in the painted turtle, ChrysAmys
picta (Gibbons and Tinkle, 1969) and in several
species of lizards (Turner, Medica and Smith,
66
1973; Mayhew, 1966a,b, and 1967; Vinegar, 1975;
Zwiefel and Lowe, 1966).
Similarly, Swingland
and Coe (1978) showed that the most important
factor influencing annual reproduction in Geochelone gigantea is rainfall.
Increased rainfall
results in increased oviposition or egg mass;
increased egg mass increases survivability of
hatchlings (Swingland and Coe, 1979).
Increased
oviposition can be manifested either in increased
number of clutches or in clutch size.
Hahn and
Tinkle (1964) observed that if Uta stansburiana
entered hibernation with an accumulation of fat
bodies (as a result of high forage quantity
caused by heavy summer rains), early oviposition
was possible the following spring; essentially
none of the fat bodies were used for survival
during hibernation.
If forage production
was adequate in the spring, the likelihood of
multiple clutches would be high.
has not been investigated to
~-
This situation
agassizi although
Berry (1978) has suggested that the number of
clutches varies with forage availability.
How-
ever, Turner (1981, in press) found that after a
winter drought, which resulted in a 100-fold
decrease in vegetation from the previous year,
double clutching still occurred and was not
significantly less than in the previous "good"
67
year.
He suggested that tortoises may have
switched to cactus as the main food source in
the drought year, leaving one to speculate on
the adequacy of alternative food sources.
Clutch size, while apparently correlated
to rainfall, is also the product of the age of
the female.
Fitch (1970) postulated this for
most reptiles.
Gibbons and Tinkle (1969) noted
that in many species of reptiles, including the
slider turtle, Pseudemys scripta elegans (Cagle,
1944 and 1950), the mud turtle, Kinosternon
bauri (Einem, 1956), and the common musk turtle,
Sternothaerus odoratus (Tinkle, 1961), there was
a strong correlation between clutch size and
body size, although they did not find this to be
true for the painted turtle, Chrysemys picta.
Data concerning this phenomenon with regard to
~·
agassizi are unavailable, although it may
well be a factor influencing recruitment.
Reproductive senescence may also be important,
having been observed in a few species of turtles
(Cagle, 1944; Gibbons, 1969; Legler, 1960;
Tinkle, 1961), but not in the Aldabran tortoise,
G. gigantea (Swingland et al., 1979).
Nest mortality would be influenced by predation and desiccation.
Eggs are buried to a
depth of only 2 to 6 inches (Berry, 1972;
68
Burge, 1977; Coombs, 1977b) and would consequently
be easily accessible to excavation by Gila rnonsters (Coombs, 1976), badgers, coyotes (Coombs,
1977b), kit foxes (Coombs, 1976), and skunks,
especially in the sandy loam found in most areas
inhabited by tortoises.
However, female
~·
agassizi urinate on the nest, possibly as a predator defense (Patterson, 1971).
Swingland and
Coe (1978) similarly suggested that urination on
the nest by female
~-
giantea creates a "concrete"
barrier to excavation by predators and confuses
olfactory cutes to the exact nest location.
Additionally, they suggest that a sterile and
humid environment for the eggs results.
Coombs
(1977c) also theorized that urination on the nest
by the female
~·
agassizi might compact the soil
and aid in the prevention of desiccation.
3)
Mortality rate--Obviously, this should not exceed
the survival rate as
~·
agassizi, primarily a K-
selected species, is probably subject to little
population cycling.
4)
Amount of land occupied by the population--The
minimum size for viability has yet to be established; however, Berry et al.
(1979) suggested that
the minimum size for a population
rni
2
~
200 tortoises/
2
is 100 rni , based on the number of available
horne ranges for adult males.
It may follow that
69
a population with 50-100 tortoises/mi 2 (i.e.,
the majority ofi the high
den~~ty
populations in
Nevada) would require a minimum of 25 to 50 mi. 2
5)
Quantity of land currently and potentially available for tortoise habitation--This would include
areas unaffected by major habitat alterations
(e.g., urbanization; agricultural development;
topography) .
6)
Amount of current and pending disturbances and
their effects on the population--Human-related
disturbances and their impacts include:
(i)
O.R.V. use--This can cause immediate and
long term damage to tortoises.
The former
occurs when tortoises are overrun while
active or buried alive in their burrows.
Additionally, Brattstrom and Bondello (1980)
found that the noise of motorcycles and dune
buggies can temporarily or permanently
deafen some desert vertebrates, leaving them
them vulnerable to predation or potentially
fatal abnormal behavior.
The desert tortoise
has well-developed middle and inner ears
(Miles, 1953) and has been reported to
hear a vehicle horn at distances greater
than 50 yards (Coombs, 1977c).
If audition
is an oft-utilized sense, which would be
indicated by its development, then deafening
70
by engine noise might be significant.
Long term habitat destruction by O.R.V. 's
is manifested in vegetation removal (Keefe
and Berry, 1973) and inhibited restoration
of vegetation (Wilshire et al., 1978).
Plants are crushed and uprooted and their
root systems disturbed by direct O.R.V. impact.
Soil disturbance results in wind and
water erosion, which undercuts root systems
and buries vegetation on the disturbed
site and in adjacent areas.
Loss of the
fertile upper layers reduces germination
potential (Wilshire and Nakata, 1976; Wilshire et al., 1978.
Temperature regimes
within the soil are altered as a result of
canopy loss and physical modifications of
the soil.
Compaction of the soil reduces the
soil moisture by inhibiting penetrability
by root systems.
The "life expectancy" of
O.R.V. tracks in the desert can be anticipated by observation of 1) Indian intaglios
near Blythe, California, which were made
several hundred years ago simply by scraping
away the desert pavement, 2) wagon wheel
tracks near
Ne~dles,
California, which are
still visible after a century, despite their
disuse for the past 80 years, and 3) tank
71
and jeep tracks made during Patton's war
maneuvers in the 1940's near Vidal Junction,
California (Wilshire et al., 1976) and
maneuvers near Needles, California in the
1960's (Karl, l980a), which are still highly
visible.
Berry et al.
(1979) has documented
several cases where declines of tortoises,
as well as other desert vertebrates, appears
to be the result of O.R.V. use.
The construction of roads, e.g., access
roads for transmission lines, mines, or oil
exploration, would have similar results on
the vegetation and soil structure as those
caused by O.R.V. use.
(ii) Livestock grazing--Hardy (1976) stated that
livestock grazing has been a major contributor to the decline of the tortoise popula-:
tion on the Beaver Darn Slope in Utah.
Gra-
zing results in direct negative impacts,
such as crushing of young tortoises, destruction of burrows (Berry, 1978; personal observation), and destruction of and competition
for forage.
Plants are trampled and
uprooted (Berry, 1978; personal observation).
Bedding and watering sites are especially
susceptible to immediate forage loss; in
72'
addition the soil is compacted, which
increases the restoration time for revegetation (Webb and Wilshire, 1980).
Where
sheep are grazed, the impacts are greater.
Webb (1978, in Berry et al., 1979) noted
that sheep ate 60 percent of the annuals and
trampled an additional 24-28 percent in a
single pass through an area in the western
Mojave Desert in California.
The cover of
perennial shrubs was also reduced.
Coombs (1979) fo1md a 37 percent dietary overlap between G. agassizi and cattle.
Berry (1978) suggested that reduced reproduction occurs in response to unsuccessful
competition with cattle for existing forage;
however, Turner (1982, in press) failed to
substantiate that "unsuccessful competition"
occurred during a two-year study.
It is
possible that adult females may suffer fatal
stress as the combined result of the high
energy demands of reproduction and the
inability to replenish vital fat reserves if
forage is reduced in response to grazing
pressure and/or drought (Berry, 1978).
It is likely that the long term, negative impacts of grazing, rather than current
impacts, effect the greatest decrease in
73
tortoise densities because of the change
in habitat which results from the reduction
of native annuals and perennials and the
introduction of successful exotics.
et al.
Hohman
(1978) found that U.S.G.S. reports
for the Beaver Dam Slope in western Arizona
in 1870 and 1901 indicated that perennial
grasses were relatively abundant.
In 1948,
Woodbury and Hardy stated that they were
aware of a decline in perennial grasses on
the slope in Utah, but that the perennial
grass, Muhlenbergia porteri, remained a
major food item for
~-
agassizi.
Recent
reports by Coombs (1978) state that perennial
grasses, including
~·
p~rteri,
are scarce
on the Slope, except where exclosures prohibit livestock grazing.
Of the 21 annual
and perennial grasses currently found on the
slope in Arizona, 8 are exotic (Higgins, no
date, in Hohman et
~1.,
1978).
Coombs
(1977a) suggested that the 7.49 percent
annual decline in the Slope's Utah Tortoise
population is due in large part to vegetational changes resulting from livestock
grazing.
A dominance of Bromus rubens_, which is
a grazing-introduced annual (Robbins et
~l·'
74
1951) is probably indicative of extensive
grazing, either temporally or spatially.
(An exception to this may occur in the
Coleogyne ramasissima community and C.
ramosissima-Larrea tridentata ecotone, where
the often-observed predominance of B. rubens
may be the result of the increased tolerance
of this species to the climatic regimes
imposed by these communities, rather than
the result of overgrazing.)
Interestingly,
the common occurrence of Astragalus sp. and
Lotus sp. in areas of dominant
~·
rubens,
may constitute a similar indicator of the
degree of grazing if one considers that many
legumes require scarification of the seed
coat for germination; this would probably
be accomplished in the bovid digestive
system.
In fact, livestock has grazed in
eastern Nevada (where B. rubens was often
predominant) since the mid-1800's (Hohman
et al., 1978).
Consistent with the hypo-
thesis presented earlier, estimated tortoise
densities in areas of Nevada where B. rubens
appeared to be predominant were significantly
low.
B. rubens has also been shown to
adversely affect the success of the rodent,
Dipodomys microps, in Nevada (Beatley, 1966).
75
Although introduced annuals are commonly
eaten by tortoises, their palatibility or
nutritive value may be less than that of
native annuals or perennials.
This may be
especially important if the exotic species
are successful to the exclusion of natives.
The latter often seemed to be the situation
with regard to
~-
rubens, although Beatley
(1966) concluded that there was "no evidence
that the numbers of the • .
annuals.
. native winter
(were) reduced because of
sharing a site with B. rubens."
Coombs (1978) proposed that reduced
reproduction in
~·
agassizi would follow the
obligatory dietary switch due to altered
vegetation from long term grazing.
With the
loss of perennial grasses, which provide
water and nutrients unavailable in annual
forbs, females might not be able to afford
to urinate on the nest, the potential adverse
effects of which were previously discussed.
Or, if the female urinated on the nest, she
might not be able to replenish the bladder's
supply of water and thus would be faced with
potentially toxic levels of bladder solutes,
especially potassium.
Minnich (1977)
reported that no reptile can withstand
'
'
76
chronic elevated levels of potassium and
that high cellular concentrations of potassium ions disrupt DNA replication, RNA synthesis, enzyme activity and processes in the
nervous system.
Coombs (1978) suggests that
reproductive capability is thus altered.
Dehydrated tortoises secrete potassium
from their cells to maintain non-disruptive
levels of cellular potassium.
This surplus
potassium is subsequently stored in the
bladder.
Normally, it is excreted as a
gelatinous urate precipitate, but if a tortoise is faced with potential desiccation
because of a lack of standing water or free
water in plants, it can ill afford to
excrete water.
This results in elevated
levels of bladder potassium.
To maintain
non-toxic levels of potassium, tortoises
estivate during hot summer months to avoid
water loss when only dried forbs, which are
high in potassium (Minnich, 1977) are available.
Perennial grasses which would not
only constitute a source of free water, but
their potassium content is below that of
annuals commonly consumed by tortoises
(Coombs, 1979).
(iii) Vandalism--The effects of vandalism on
77
tortoise populations are probably minor.
I have found tortoises which were shot and
Berry et al.
(1979) related observations of
shot and cut tortoises and of some that were
apparently deliberately crushed by vehicles.
(iv) Collecting--Collections of tortoises, especially near main roads and urban areas has
probably had greater effects in the past
than presently because of the current protected status of the desert tortoise.
Coombs (1977) estimated that declines in the
density of the tortoise population on the
Beaver Dam Slope in Utah were, in part, the
result of a 2.2% annual collection rate.
Berry et al.
(1979) reported similar
findings for populations of tortoises in
California.
Bob Turner of the Nevada Depart-
ment of Wildlife Resources (personal communication) estimates that there are currently
20,000 to 40,000 captive tortoises in Las
Vegas.
Of the ten areas in Nevada with estimated densities
2
exceeding 50 tortoises/mi , the Pahrump, Goodsprings Valley,
Dry Lake Valley, Coyote Springs Valley and Eldorado Valley
populations may be too small to survive.
Additionally,
several factors may contribute to the extinction of these
populations.
The urban expansion of Pahrump may force
78
tortoises there to move further south into the valley.
Although land is available for expansion, the low tortoise
densities currently estimated for the valley may be indicative of sub-optimum tortoise habitat.
Goodsprings is
topographically isolated, except to the north, towards
Arden, which offers no refuge, as the Arden population will
surely be destroyed by urban expansion from Las Vegas.
The
Dry Lake Valley population, while connected to the Hidden
Valley population, will probably be lost due to fragmentation by Interstate Highway 15 and disturbance, as well as to
its small size.
Only the Eldorado Valley and Coyote Springs
Valley populations, which have open corridors to other high
density populations and potentially adequate reserves of
available tortoise habitat, may be viable.
This is probably
especially true for the connected Coyote Springs Valley and
Hidden Valley populations, which experience relatively
little disturbance.
The Virgin Mountains and Piute Valley populations, and
less so the Moapa Valley population, are probably the most
viable populations by virtue of their size, lack of disturbance and/or amount of available tortoise habitat.
However,
current and pending land uses and their effects on these
populations must be carefully monitored and controlled to
insure their survival.
As an example the Piute Valley
population, while comprising an apparently high density of
tortoises, sustains a moderately high and potentially
unhealthy degree of disturbance.
In a 1979 study of a 1
79
square mile subpopulation of tortoises in Piute Valley
(Karl 1979a), it was determined that natality was low,
evident in the low proportion of tortoises under 100 rom
in carapace length (5 percent) and an unfavorable sex
ratio (0.68 females:l male).
80
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Schwartzmann, and R. Ohmart.
1977. Radiolocating freeranging desert tortoises (Gopherus agassizi) :
maximizing transmitter range and longevity.
In:
Trotter, M. (Ed.), Desert Tortoise Council Proceedings, 1977 Symposium. Las Vegas, NV.
Pp. 57-58.
1976. Preliminary investigation of a desert tortoise,
Gopherus agassizi population in Pinal County, Arizona.
In: Engberg, N., S. Allen and R. Young.
(Eds.),
Desert Tortoise Council Proceedings, 1976 Symposium.
Las Vegas, NV. Pp. 75-76.
Sheppard, G.
1982. Status report of the Beaver Dam
Slope desert tortoise population.
Unpublished report.
30 pp.
State of Nevada, Division of Water Resources.
1:1,000,000 vegetation map of Nevada.
1971.
Swingland, L. and M. Coe.
1979. The natural regulation of
giant tortoise populations on Aldabra Atoll. Recruitment. Phil. Trans. R. Soc. Lond. B. 286:177-188.
1978. The natural regulation of giant tortoise
populations on Aldabra Atoll.
Reproduction.
J.
Zool., Lond., 186:285-309.
Taubert, B., 1982. Arizona Game and Fish Department
Wildlife Managers' survey of desert tortoise distribution in Arizona.
In;
Desert Tortoise Council
Proceedings, 1982 Symposium. Las Vegas, NV.
In
press.
86.
Templeton, B. 1982. Multiple use management on desert
tortoise habitat. In: Desert Tortoise Council
Proceedings, 1982 Symposium. Las Vegas, NV. In
press.
Tidestrom, I. 1925. Contributions from the U.S.
National Herbarium--Flora of Utah and Nevada.
25. 665 pp.
Volume
Tinkle, D. 1967. Home range, density, dynamics and
structure of a Texas population of the lizard Uta
stansburiana. W. Milstead, ed. Lizard ecology-,-a
symposium. Kansas City, Univ. No. Press, 1967:
5-31.
1961. Geographic variation in reproduction, size
sex ratio and maturity in Sternothaerus odoratus
(Tesudinata: Chelydridae). Ecology, 42:68-76.
Turner, F., P. Medica, and C. Lyons. 1982. The desert
tortoise in grazed and ungrazed areas in Ivanpah
Valley.
In: Desert Tortoise Council Proceedings,
1982 Symposium. Las Vegas, NV. In press.
Turner, F., P. Medica and D. Smith. 1973. Reproduction
and survivorship of the lizard Uta stansburiana and
the effects of winter rainfall, density and predation on these processes. S/IBP Desert Viome Res.
Memo., 73-26.
Turner, R. 1981. State Report--Nevada. Department of
Wildlife Resources.
In: Desert Tortoise Council
Proceedings, 1981 Symposium. In press.
1980. State Report--Nevada. Department of Fish and
Game. In: Hashagen, K. (Ed.), Desert Tortoise
Council-proceedings, 1980 Symposium. Riverside, CA.
Pp. 88-90.
U.S. Department of Agriculture, Soil Conservation Service.
Soil classification, a comprehensive system. 7th
Approximation, 1960. 265 pp.
u.s.
Department of the Interior. Bureau of Land Management,
Las Vegas District. 1977. 1:500,000 Public Lands
Map.
Walchuk, S. and J. Devos. 1982. An inventory of desert
tortoise population near Tucson, Arizona. In:
Desert Tortoise Council Proceedings, 1982 Symposium.
Las Vegas, NV. In press.
87
Webb, R. and H. Wilshire.
1980. Recovery of soils and
vegetation in a Mojave Desert Ghost Town, Nevada,
USA. Hasagen, K. (Ed.), Desert-Tortoise Council
Proceedings, 1980 Symposium, Riverside, CA. Pp.
117-135.
Wilshire, H. and J. Nakata.
1976. Off-road vehicle
effects on California's Mojave Desert. California
Geology, 29:123-132.
-----, S. Shipley and J. Nakata.
1978.
Impacts of offroad vehicles on vegetation. Trans. of the 43rd
North American Wildlife Conference.
Pp. 131-139.
Vinegar, M.
1975. Demography of the striped plateau
lizard, Sceloporus virgatus. Ecology, 56:172-182.
Woodburn, A. and R. Hardy.
1948. Studies of the desert
tortoise, Gopherus agassizi. Ecol. Monogr., 18-145200.
Zwiefel, R. and c. Lowe.
1966. The ecology of a population of Xantusia vigilis, the desert night lizard.
Am. Mus. Nov., No. 2247:1-57.
88
Appendix I.
Estimated Relative Densities and Distribution of Gopherus agassizi in Nevada.
89
Appendix I.
L''"'J
Estimated Relative Densities of Gopherus
agassizi on Public Lands in Nevada.
(Note:
Densities are derived from a combination of
TAS and burrow sign.)
2
0 Tortoises/mi
,,_ ,.,.., 1,......v
;:_~~t'
I •./
-;::,
,, t.:. 0-10
11-50
11-100
51-100
51-150
101-150
101-200
4000 foot contour
Study area boundaries
kZ2ZZ4
1 mile
11'1
z cE(--f----
VNOZIH
z
....
·--·--·--·--------...__·-·-·___.·-~--
LLI
z
91
Appendix II.
Major Shrub Communities in Southern Nevada.
92
Appendix II.
.....
.....
......
......
.....
'
'
'
Major Shrub Communities in Southern Nevada.
(Note: Plant communities outside of the study
area are obtained from reports from Beatley,
1976 (for Nye County); B.L.M., no date;
N.D.W.R., 1971: and Tidestrom, 1925 (for
Clark and Lincoln counties).)
Larrea tridentata-Ambrosia dumosa or
Atrlplex confertifolia
'
Coleogyne ramosissima
L. tridentata-C. ramosissima ecotone
Pinus monophylla-Juniperus osteosperma
~
4000 foot contour
Study area boundaries
I<Z:ZZZ2Z2I
1 mile
93
Cl
:z
0
T
T
94
Appendix III.
Transect Data Form.
95
TEST FORM
[1 I RECORD TYPE
[2] STATE
[3] DISTRICT
[4] PLANNING UNIT
CALIFORNIA DESERT PROJECT
STANDARD UNIT RECORD
FOR
DESERT TORTOISE SURVEY
w
2
/)
()
/.-
!/
0
.:;;;...-
r
~
L1
[5] SITE NUMBER
:...-;
[6] COUNTY
[7] ACTION [A= ADD C=CHANGE D=DELETE]
[8] SECTION I
GENERAL SITE DESCRIPTION
i 91 DATE OF SURVEY
YR./MD./DAY
[11 j RECORDER
-'1''11
/'f.;<,,...;
p.r
?Cj'r'/11
'1
1101 HOUR
i: GEOMORPHOLOGY
i201 VEGEiAL
TYP:~
--·"".;t
~_)
?- 'l 'fCI
J...;~
181 SECTION II
J'
ASPECT
v
/lf.u,oc;_
SITE NAME
/?,. r- H~~A
4Mi"
AI-"""'"
LOCATION DATA
!11] RANGE
~3<t:
I
/I:>
181
I
I
I
'
,
?-<10
"
;4'
!111
112]
WIDTH
HEIGHT
;(, ~
/
,-,"
;.??
04
::.:o.S
;:J.o/0
06
;:..6
;"i3
03
05
p~
1•13i SUBDIVISION
I
I
I
[141 ZONE
_A/
{151 NORTHING
..,.._r
...,.,..
i13i SOIL
COVER AT
ENTRY
11
12
13
1(
15
"'"'
cld'
I
I
[161 EASTING
-,-(,
B''~
(&,'?
-¥v
-.e. ...zd-
.4
[15j
[161
i171
118!
[19!
LOCATION
SCATS
SIZE
CONDITION
LOCATION
.
'f
"33
~s
.../X>
{141
CONOmON
.3
'
(.
:;:_
"'
.......
~
,_·::;..-:,.,.
;·~
'%
"--"'
:;:_
"'
/~
)
07
10
.-'!"ii:.:>
/0 _,
SCATS
08
09
'23' WICTH
1
BURROW AND SCAT DATA
1101
02
G
-""~
,k'a...t..L SPc-P~ .1<.]._ ""
BURROWS
01
% AVG.
S:
kJ
'22' LENGTH iFEET:
7/-'?;Aa •
..rCP1.--..
JV. .tV
SEC liON Ill
LENGTH
i16! SLOPE
UTM GRID'LOCATION
1121 sEcnoN
;g:
i..IHc:
I
TRANSEC':'
(A;A.r.u.; ;- q . ~
CADASTRAL GRID LOCATION
!101 TOWNSHIP
1
/
.21' HABITAT
~IT JON
t:~
[9J TOPOGRAPHIC DUAD
SCALE
:;z ...,-,
we•THEn CDHOITIDNS
[15i ASPECT
.,., CLOUD COV
"13' TEMP.
;')~
f19i TEXTURE
i18i ELEVATION
.$1-j'~ -u/1-"J
[121 WJNOSPEED
.
96
LIVE TORTOISE. SHELLS. SHELL PARTS DATA
[ Bj SECTION IV
i 13;
TYPE
REPORT
:L-or-s:
!9'
LIN I
•
[11i
[12~
[13!
[14>
! 15;
'16>
SEX
SIZE
LOCATION
ACTIVITY
CONOmON
AGING
01
02
I
03
04
05
06
07
08
I
09
i
10
I
12
UBI
SECTION
lll~E
I
> .
rol .
v
l
I
I
11
i
l
TRACKS DATA
!10!
[11l
[12~
!131
WIDTH
SEX
LOCATION
AGE
I
COURTSHIP RINGS
1141 LENGTN
I
I
'15; WIDTH
l
l
oz
I
03
i
04
l
I
05
I
I
06
07
I
08
REMARKS:
#
.......
~~
~· ~ ~-
a..,·
...
sltM'- ,:;&~,,.. »!cct'-~
j'~"lhy 4-- ~--7;.-(..Jt ~or-.
I";. .lf/_k
~6,..e
~~
~)1 ~ ~
.4-.<!-
~z/·, ~) ~~'-'J).
a-:.-uPr
5~-
v~ s~
~- r-
~~·7 ~~
I
l
I
S7
Appendix IV.
Sign Located
on Transects
"'"
Appendix IVA.
Transect
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Sign located on Lincoln County transects.
Legal
Description
Tl2S R63E S29
Tl2S R64$ S31
Tl2S R63E S2
TllS R63E S29
TllS R63E Sl4
TlOS R64E Sl8
TlOS R64E S9
'I'lOS R65E S56
T9S R65E S6
T9S R65E S52
T8S R67E Sl4
T9S R67E Sl9
T9S R66E S2
T9S R66E Sl6
TlOS R67E S3
TlOS R66s
Sl2, 13' 14
Tl2S Rl5E S35
Tl2S R66E Sl7
Tl2S RyyE S27
Tl2S R66E Sll
Tl2S R66E
S21, 22' 27' 28
Tl2S R69E
Sl9,20,29,30
Tl2S R68E S35
Burrows
1
1
0-1
2
4-5
Individual Sign
Scat Skeletal
Remains
1
1
1
3-4
0-4
1
1
1
Live
Tortoises
Total
Adjusted
Sign
Estimated
Tortoise
Density
(# :tortoises/
mi )
1
1
0-1
3
4-5
1
0
0
0
0
0
0
0
0
3-4
11-50
11-50
11-50
11-50
51-100
11-50
0
0
0
0
0
0
0
0
11-50
0
0
0
1-5
0
0-10
0-10
1-10
11-50
0-10
2
11-50
0
0
1-10
0-10
1.0
co
Appendix IVA, continued
Transect
Legal
No.
Description
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
Tl2S R68E Sl6
Tl08 R68, 69E
825,30,31
Tll8, R69E
821, 28
Tl28 R69E 83
Tl28 R70E 820
Tl28 R70E 827
Tll, 128 R70E
831,5,6
Tll8 R70E
810,15
Tl08 R70E 826
Tll8 R71E 816
Tl28 R71E
810, 15
Tll8 R71E 830
Tl08 R71E 833
Tl08 R71E
817, 7,8
T98 R71E
89,16,17
T98 R70E
816,17
T98 R70E 832
Tl08 R69E 810-3
Burrows
2
Individual Sign
Scat
Skeletal
Remains
1
2
1
0-1
1
2
2
Live
Tortoises
Total
Adjusted
Sign
Estimated
Tortoise
Density
(#tortoises/
mi2)
0
0
0
0-10
0
0
3
0
0-10
1-10
11-50
11-50
0
1-10
0
0
2
1-10
1-10
11-50
1
3
3
11-50
11-50
11-50
0
0-10
0
0
0
0
0
0
0
0-10
\.0
\.0
Appendix IVA, continued
Transect
No.
42
43
44
45
46
47
48
49
50
51
52
Legal
Description
Burrows
TllS R69E Sl2
TlOS R70E S31
TlOS R68E
Sl5,22
T9S R68E
S25,36
1
T9S R69E S4
T9S R69E S23
TlOS R68E S5,6
T9S R68E Sl0,15 1-2
T9S R67E Sl3,14
TlOS R67E Sl4,23
TllS R66E S8
Individual Sign
Total
Scat
Skeletal
Live
Adjuste.d
Sign
Remains Tortoises
0
0
1
1-10
1-10
0
0
0
1
0
0-10
11-50
0-10
0-10
11-50
11-50
0-10
0-10
0
1
1
Estimated
Tortoise
Density
(# tortoises/
mi2)
2-3
2
0
0
I-'
0
0
Appendix IVB.
Transect
No.
Sign located in Nye County transects
Legal
Description
Burrows
Individual Sign
Scat
Skeletal
Remains
Live
Tortoises
Total
Adjusted
Sign
Estimated
Tortoise
Density
(# tortoises/
rni 2)
T20S R52E
Sl5,22
0
0
2
T20S R52E S5
0
0
3
Tl9S R51E
S23,24
3-6
11-100
0
0-10
1
2-5
4
Tl9S R51E S5
5
Tl8S R51,52E
S25,30
2-4
6
Tl9S R52E S4
3
7
Tl8S R52E
S23,24
1
8
9
10
1
6
2
Tl9S R52,53
Sl3,24,18
1
Tl7S R51E Sl9
2-4
11-50
5
11-50
1
11-50
0
0
1
11-50
Tl8S R51$
Sll,4
1
1
11-50
11
Tl7S R52E Sl75
1
1
11-50
12
Tl8S R52E S3
1
11-50
13
Tl7S R51E S28
1
11-50
1
1
1--'
0
1--'
""
Appendix IVB, continued
-
Transect
No.
Legal
Description
14
Tl7S R52E S23
15
Tl6S R52E
S33,34
-
Burrows
0-2
Individual Sign
Skeletal
Scat
Remains
Live
Tortoises
Total
Adjusted
Sign
Estimated
Tortoise
Density
( # tortoises/
.mi )
0
0-10
0-2
0-50
16
Tl6S R52E S5,8
0
0-10
17
Tl5S R51$
S22,23
0
0-10
Tl6S R51E
Sl4,15,22,23
0
0-10
19
Tl6S R51E Sl7
0
0-10
20
Tl6S R53E S5,8
0-2
0-50
21
Tl6S R53E S24
0
22
Tl5S R50E
S9,16
0
0-10
0-2
0-50
18
23
Tl5,16S R50E
S31,6
0-2
0-2
0
24
Tl6S R50E S28
0
0-10
25
Tl5S R49E S23
0
0-10
26
Tl5S R49E S30
0
0-10
27
Tl5S R47E
S27,28
0
0-10
1-'
0
N
"'"
Appendix IVB, continued
Transect
Legal
No.
Description
Burrows
Individual Sign
Scat
Skeletal
Remains
Live
Tortoises
Total
Adjusted
Sign
Estimated
Tortoise
Density
(#tortoises/
mi2)
28
Tl5S R47E Sl8
2-3
2-3
11-50
29
Tl.4S R47E S30
1-4
1-4
11-50
30
Tl4S R48E S5,8
0-1
0-1
0-10
31
Tl4S R48E S7,18
0
0-10
32
Tl4S R47E S35,36
0
0-10
33
Tl4S R48E S27
0-3
0-3
0-50
34
Tl3S R48E Sl5
1-3
1-3
11-50
35
Tl2S R48E S24,25
0
0-10
36
Tl3S R471/2E Sl2
0
0-10
37
TllS R48E S33
0
0
38
Tl2S R48E Sl7
0
0
39
TllS R47E S23
0
0-10
40
TllS R47E Sl7
0
0-10
41
Tl2S R46E S7
0
0
42
Tl2S R46E S34
0
0-10
43
Tl3S R46E
S23,24,25,26
0-1
0-10
0-1
1-'
0
w
Appendix IVB, continued
Transect
No.
Legal
Description
Burrows
Individual Sign
Scat
Skeletal
Remains
Live
Tortoise
Total
Adjusted
Sign
Estimated
Tortoise
Density
( # tortoises/
mi2)
44
Tl4S R46E Sl8
45
Tl3,14S R45E
Sl2,32,33
1
1
11-50
0
0-10
0-1
0-10
1-2
11-50
46
Tl3S R46E S21
0-1
47
Tl3S R46E S3
0-1
48
Tl2S R46E S3
0
0-10
A
Tl8S R51E S21
0
0-10
B
Tl9S R51E S3
0
0-10
c
Tl9S R51E Sl3
0
0-10
3
1-'
0
,j:>.
"'"
Appendix IVC.
Sign located on Clark County transects
---·
:.=-==--=~=:.....--==·-=·::.-==-~
Transects
No.
Legal
Description
Burrows
1
Tl6S R63E S29,30
2
Tl5/16S R63E S33/4
2-5
3
Tl5S R63E S20
4-5
4
Tl5S R63E S3
0-1
5
Tl4S R63E
S20,21,29
0
6
Tl4S R63E S3, 4
1
7
T13S R62E S6
8
Tl3S R63E S23,24
Tl3S R64E S22,26,27
9
10
Individual Sign
Scat Skeletal
Remains
- --
Live
Tortoise
- • . ····-------
Other
1
1
-=-=--.-=.:.:.._-:::-:;;:.
.::::-.·:·.·-~
Total
Adjusted
Sign
Est.imated
Tortoise/
·2
IDl
1
l-10
1
1
2-5
51-100
1
1
5-6
51-100
0-1
0-50
1
1
1-10
0·-50
0
0-10
3
0
11·-50
1
3
0-10
T13Vl4S R63E
S33/4
3
3
11-50
11
T13S R64E S7
3
4
11-50
12
Tl3S R65E S31
1-3
1-3
11-50
13
Tl4S R65/66E
S13/18
5-6
8-9
51-100
0
0-10
1-2
11-50
2
11-50
14
'I'l4S R65E Sl7
15
T13S R65E Sl
1-2
16
Tl4S R66E S23
1
1
2
1
2
1
Tracks
1
I-'
0
1.:/J
Appendix IVC, continued
--- - --
Transects
No.
·- ··-
·-==-····-=-====·-·=-=.:-.:=..
Legal
Description
-·
Burrows
--
Individual Sign
Scat Skeletal
Eemains
17
Tl4S R66E S3,4
18
Tl4S R67E S7
3
1
19
Tl3S R67E S8
1
1
20
Tl3S R66E S36
1-3
21
Tl3S R68E S4
4
22
Tl3S R69E SS
1-2
23
Tl3S R69E
Sl4,15,23
24
25
-
-----
.·:.;.;-:::;-..:.-=-.....:::....,;_.....;.=-=:::---..:.:-:.;.:..:~...-::-.
Live
Tortoise
Other
1-2
8
7
Tl3S R68E
S21,28
8-9
1
1
26
Tl4S R67E S23,26
2
27
Tl3S R66E S29,32
3
28
T15S R69E Sl2
29
30
T15S R69E Sl5 22
T16S R69E Sl,2
31
T16S R69E S21
5--6
0-1
3-4
1
3
'1'13S R67E
S23,26
I
-
7
Tracks
1
Tracks
1
•
~:.::::
...;:.;:__::-:~
.. ..:..:.:... ...:.-·.::..
~----·--
'Ibtal
Adjusted
Sign
Estimated
1-2
11-50
4
11-50
2
11-50
4-6
51-100
4
11-50
1-2
11-50
0
0-10
9
0-10
8-9
51-100
2
11-50
3
11-50
'Ibrto~zel
Till
51-100
2
0-1
=·-=--
1
0--1
3-4
0-50
11-50
0
0-10
I-'
0
,0)
Appendix IVC, continued
=-=-.:.::..==-=-::...:.=~~~:....=.:.
Transects
No.
Legal
Description
32
Tl6S R70E S21,29
33
34
Tl7S R70E Sll
Tl7S R70E Sl9
35
36
Tl8S R69/70E S6,7
Tl8S R69E
Sl3,14,23,24
37
38
39
40
Burrows
Individual Sign
Scat Skeletal
Rerrains
3
2
1
8-14
1
1
0-1
2
Live
Tortoise
1
Other
Tracks
1
1
Tl9S R69E Sl,l2
Tl9S R70E S2
T20S R70E Sl2, 13
Tl9S R70E S83
Total
Adjusted
Sign
Estimated
Torh?~se/
IPl
6
10-16,
101~±50
0-1
2
0-50
11-50
0
0·-10
0
0
0-10
0-10
0
0
0-10
0-10
11-100
0
0-10
42
Tl9S R69E S22,27
T20S R69E Sl4,23
0
0-10
43
T20S R70E S29, 30
0
0-10
44
Tl9S R69E S32,33
45
Tl8S R70E S23,26
0
0
0-10
0-10
46
Tl8S R71E Sl,l2
10-12
51-150
47
48
Tl6S R70E Sl3,24
Tl3S R70E S31
3
0
4
0-10
11-50
49
Tl4S R70E S2
1
2
11-50
41
4-6
3
4
1
Eggshells 1
Tracks 1
4
1
f-'
0
'<!
~~r
.
Appendix IVC, continued
--
---
Transects
No.
50
Legal
Description
BurreMs
Individual Sign
Scat Skeletal
Remains
Tl4S R70E
S21,22,16
0-1
51
Tl4S R69E S24
1-2
52
Tl3S R70E S6,7
53
Tl4S R69E S4,5
54
Tl4S R68E S3,4
55
56
Tl4S R68E S33
Tl5S R68E Sl0,11,14
57
Tl5S R68E S31,32
58
Tl7S R66E S28,29
0-1
59
Tl9S R63E Sl6,21
1
60
Tl9S R64E S9
1
61
Tl8S R64E S25,26
62
Tl8S R65E S8
2
1
2
63
Tl7S R64E S36
3
2
1
64
Tl7S R65E S27
0-1
65
Live
Tortoise
1
Other
'Ibtal
Adjusted
Sign
Estimated
Tortc:>~se/
I)U
0-1
0-50
1-2
11-50
1
1-10
0
0-10
2
11-50
3
0
1-10
0-10
0
0-10
1-2
1-50
1
2
11-50
11-50
0
0-10
5
11-50
6-9
11-100
0-1
0-50
Tl8S R65E
813,14,23,24
0
0-'-10
66
Tl9S R65E Sl
0
0-10
67
Tl8S R66E S28,29
1-2
1-10
1
2
1
0-1
2
1
1
1
1
··-
......
0
00
Appendix IVC, continued
Transects
No.
legal
Description
Burrows
Individual Sign
Scat Skeletal
Remains
Live
Tortoise
Other
Total
Adjusted
Sign
Estimated
Tortoise/
mi2
Tl9S R66E S2,3
1
1
11-50
0-10
70
Tl8S R67E Sl9
Tl9S R66E S24,25
2
0
1
1
2
11-50
71
Tl8S R67E S33
0
0-10
72
Tl5S R67E SlO,ll
0
0-10
73
74
75
Tl5S R67E S20
Tl6S R67E S26,35
Tl8S R66E S3
1
1-10
0
0-10
0-10
76
2
77
Tl7S R65E Sll
Tl7S R66E S8
0
2
1
1
78
79
Tl6S R66E Sl5, 22
Tl6S R65E Sl4,15
1
2
3
1
80
Tl6S R66E S8,17
3
81
82
Tl5S R66E S29,32
1
83
84
Tl5S R66E Sl5
Tl5S R65E Sl4
Tl5S R65E S31,32
1
2
0-1
85
Tl5S R64E Sl0,15
1-2
68
69
1
1
1
1
4
5
1
3
2
2
1
0-1
2
1
1
3-4
1-50
1-50
11-50
1-50
11-50
11-50
11-50
11-50
0-50
11-50
I-'
0
1.(5
Appendix IVC, continued
.4
Transects
No.
Legal
Description
86
Tl5S R64E S20
87
88
Tl4/15S R64E
S32/5
Tl6S R64E S2
89
Tl6S R65E #31, 32
90
91
92
Tl8S R64E S8
Tl6S R64E Sl7
Tl7S R64E Sl6
93
94
95
Tl7S R63E S26
Tl7S R63E Sl7
Burrows
Individual Sign
Scat Skeletal
Remains
Live
Tortoise
Estimated
0
0-10
1
5
1-10
11-100
4-5
11-50
1
3
1
3
11-50
11.;...50
Other
1
3
2
3-4
1
2
1
Tl8S R63E S7,8
2
4-5
2
96
Tl8S R63E Sl4
9-10
3
97
Tl9S R62/63E
S6,7/12
2-4
T25S R59$ Sl7,18
T25S R59E S35
11
0-1
1
1
0
2
1
Tortc:~se/
In1
0-10
11-50
11-100
1
1
5-6
3
2
12-14
101-150
3-5
11
11-50
101-150
0-1
0-50
1
1
--:=..=--:.=
Total
Adjusted
Sign
1
Eggshells
1
11-50
98
99
100
T26S R59E S6,7
0
1-10
101
T27S R62E S29,32
0
0-10
102
T28S R62E SlO
1-2
0-10
1-2
I-'
I-'
0
"'"
Appendix NC, continued
Transects
No.
Legal
Description
Burrows
Individual Sign.
Scat
Skeletal
Remains
Live
Tortoise
Other
Total
Adjusted
Sign
Est.imated
Tort<;>~se/
IDl
103
T28S R62E S28,33
0-1
0-1
11-50
104
T29S R62E S2
1-2
1-2
0-50
105
T29S R63E S8
0-2
0-2
11-50
106
T29S R62E S28
4-7
4-7
0-50
107
T29S R63E S27,28
1-2
2
3-4
51-100
108
T30S R63E 87,8
8-10
1
3
11-50
109
110
T31S R63E Sl4,15
2
1
T30S R63E S34
10
4
11-13
11
111
T30S R63E S34
12-13
2
112
T30S R63E S34
2-5
3
113
T31S R64E S30
4
114
T32S R64E Sl4
1-2
115
T33S R65E S2,3,11
116
T32S R66E S8
117
T32S R65E Sl6
118
T32S R65E S5
119
T31S R64E S23,24
2-3
1
120
121
T30S R64E S34
2-3
2
T29S R64E S32
8
7
Tracks
2
101-150
7
13-14
101-150
4-7
101-150
4
11-100
2-3
11-50
2
2
11-50
0-1
0-1
11-50
0
0-50
4
0-10
6-7
11-50
3-4
11-100
10
11-50
3
4
1
3
3
1
Tracks
2
101-150
I-'
I-'
'I-'
,.
Appendix IVC, continued
Transects
No.
legal
Description
122
T30S R64E Sl0,15
123
T288 R63E S20
5
4
124
T28S R64E 830
6-10
8
125
T298 R64E 81,12
0-1
126
T28S R64E 85
1-2
127
T27S R63E Sl,l2
1-2
128
T288 R63E 89,10
2
129
T268 R63E 819,20
5-7
130
T268 R63$ 813
131
T258 R64E 832,33
132
T25S R64E 87
2
133
T24S R63E S25
1-2
134
T248 R63E 88,17,18
135
T258 R62E S8,17
136
T258 R62E 823
137
138
T26S %62E #29,30
139
140
T268 R62E 83,4,9,10
T278 R62E 81, 12
T278 R63$ 821
Individual Sign
Scat
Skeletal
Remains
Live
Tortoise
Total
Adjusted
Sign
Estimated
Tortoise/
nu·2
0
51-100
9
0-10
9-13
51-100
0-1
51-150
3
4-6
0-50
3
4-6
11-50
2
11-50
5-7
51-100
0
2
0-10
1-10
2
11-50
4-5
11-50
0
0-10
1
1
11-50
1
1
11-50
0
0-10
0-1
0-50
11-50
11-50
Burrows
1
Other
1
Tracks
1
2
2
1
0-1
2
1
2-4
2-4
1
2-4
I-'
I-'
rv
Appendix IVC, continred
-.--===-~===
Transects
No.
Legal
Description
141
T25S R63E S27
142
T25S R63E S8
143
T24S R64E
Sl5,16,21,22
144
Burravvs
Individual Sign
Scat Skeletal
Remains
Live
Tortoise
Total
other
~..djusted
Sign
Estimated
Toru;>~se/
rru
0
0-10
l
l
ll-50
0-l
2
2-3
ll-50
T24S R64E S35
l
2
3
ll-50
145
T23S R63E S25
0-l
0-l
0-50
146
R23S R63E S19
T21S R63E S19
0
2
1
4
0-10
11-50
T21S R63E S9
2-3
l
2-3
11-50
0
0-10
2
11-50
0
0-10
4
11-50
0
0-10
3
2
ll-50
3
11-50
0
0-10
0-1
0-50
147
148
149
Tl9S R65E S33,34
150
T20S R64E S11,12
151
T20S R64E S21
152
Tl9S R64E S30
153
T20S R63E Sl4,15
154
T20S R63E S20,29,30
l
155
T23S R60E Sl3,14
2
156
T23S R61E Sl1
3
157
T23S R61E S33
158
T24S R61E S27,28
l
l
2
2
0-l
2
3
1
ll-50
I-'
I-'
w
Appendix IVC, continued
Transects
No.
Legal
Description
159
T24S R60E S26,35
1-2
4
160
T24S %61E S7,18
1
1
161
162
T24S R60E Sl8
2
1
163
164
165
T23S R59/60E
836/31
T25S R60E S7
T24S R58E Sl0,15
Burrows
Individual Sign
Scat Skeletal
Remains
Live
'Ibrtoise
'Ibtal
Adjusted
Sign
Estimated
Tortoise/
mi2
4-5
11-50
2
11-50
3
5
11-50
1
2
11-50
11-50
other
1
1
0
1
166
T23S R58/59E
S36/31
T24S R58E S35
167
168
T24/25S R13E S35/2
T25S R13E S23
169
170
T24S R57E Sl,2
T24S R56E S25
171
T23S R56E Sl4
2-3
2-5
172
T23S R56E S30
1-2
173
174
T24S R57E S22
175
T23S R55E S15,16
0
0-10
0-10
1-10
0-2
1
1-3
0
1
1
0
1-10
1
2-3
0-10
1
3-6
1-10
11-50
11-50
1
2-3
11-50
1
1
3-4
0
3-4
11-50
0-10
T24S R56E S3
1
1
1
Tracks
1
11-50
I-'
I-'
~
Appendix IVC, continued
--
Individual Sign
Scat Skeletal
Remains
·.;.:;:::.:...._--=.=·=
'Ibtal
Adjusted
Sign
Estimated
'Ibrtoise/
·2
Till
0
0-10
1
3
11-50
3
5
11-50
3
6
11-50
Transects
No.
Legal
Description
176
T22S R55E S3,32
177
T22S R55E
S24,25,26
2
178
T22S R56E S22,28
2
1
179
T22S R56E S5,8
2
3
180
T22S R55E S3
2
1
181
182
T21S R54/55E S24/19
T21S R55E S14,15
5
1
0-1
0-1
0-50
183
T16S R55E S7
0-1
0-1
0-50
184
T16S R55E Sl3
2
1
3
11-50
185
T18S R59E S2,3
1
1
1-10
186
T185 R59E 527,28
2
4
11-50
187
T195 R59E 512
3
1-10
188
T19S R59E S5,6
1-10
189
T20S R59E 52
1
1
2
11-50
190
T215 R59E 513,14
1
8-10
51-100
191
T21S R59E 518
0-10
192
T225 R59E 53
T22S R59E S27,28
0
4-5
193
Burrows
1
2
3
1
1
3-5
3-4
3-5
6
1
2
Live
'Ibrtoise
1
Other
5-·7
11-50
51-100
11-50
11-100
I-'
I-'
(.Tf
Appendix IVC, continued
-·-~
Transects
No.
Legal
Description
Burrows
Individual Sign
Scat Skeletal
Remains
Live
Tortoise
Other
-
-
-.=-==:--=====: .. =:...=:
'Ibtal
Adjusted
Sign
Estimated
'Ibrtoise/
rni2
6-7
11-100
6-8
51-100
194
T23S R59E Sl0,15
2-3
4
195
T22S R60E S30,31
3-5
2
196
T22S %60E S7,18
10
4
19
101-200
197
T26S R60E S5,6
3
2
5
11-50
198
T27S R60E S4
0
0-10
199
T26S R60E S16,21
0
0-10
200
T26S R60E S1
1-2
11-50
201
T25S R61E S33,34
0
0-10
202
T25S R61E Sl7,19,20
0
0-10
203
T25/26S R60E
S2532/5
2--3
2-3
11-50
T26S R59E
S25,26,35,36
1
1
11-50
204
1-2
1
1-'
1-'
,0'\