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ECOLOGY OF A POPULATION OF
DESERT TORTOISES, GOPHERUS AGASSIZI ,
IN WARD VALLEY, CALIFORNIA
SPRING, 1980
Alice Karl
21126 Chatsworth St.
Chatsworth, CA 91311
Contract No. CA-060-CTO-3
Bureau of Land Management
Department of the Interior
1695 Spruce St.
Riverside, CA. 90257
SSS"*^ Manage
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ABSTRACT
Desert tortoises (Gopherus agass i zi ) were studied for
60 days during spring, 1978, on a permanent study site in
Ward Valley, California.
2
1) Density is estimated to be 63 tortoises/km ( =
2
160 tortoises/mile ) .
2) Distribution is unequal, with fewer tortoises'" in
the rock outcrops or rolling hills. Density for
2
these areas is estimated at 31 tortoises /km
2
(=80 tortoises /mi ). Density on the flats ±s
2 2
estimated to be 77 tortoises/km (=200 tortoises/mi )
3) Reproduction is high, reflected by a high percentage
of tortoises under 100 mm MCL, 24.6%, and a high
percentage of young Immature tortoises, 14.8%.
Rainfall and resultant food availability is dis-
cussed as a reason for high reproduction.
4) Mortality is estimated at 3.4 tortoises/year (=
2 . 1%/year) .
5) Females were observed to have a prominant pygal
tip while that of males pointed straight down or
was tucked under.
6) Aspects of growth, activity, burrowing behavior,
movement, feeding behavior, intra- and inter-
specific behavior are discussed.
7) The vegetation of the site was sampled to determine
present composition, biomasses, frequencies, volumes
(for perennials) and cover (for annuals).
)
INTRODUCTION
Data on the desert tortoise, Gopherus agassizi , was
collected in spring, 1980, on a permanent study site in
Ward Valley, California. The study was conducted primarily
to determine absolute density, age structure and sex ra-
tios and secondarily to examine behaviors. In addition,
the vegetation was sampled to determine absolute and rela-
tive frequencies,, volumes and densities for perennial spe-
cies and absolute and relative frequencies, covers and
biomasses for annuals.
Burge ( 1977 b and 1980 , in prep . ) studied the popul^-ion.dynamics
and behaviors of a population of desert tortoises 27 km northwest
of this site. Green and Hicks performed similar studies on
two populations of tortoises in Ward and Cadiz valleys under
contract with the Desert Plan Staff (DPS) of the Bureau of
Land Management (BLM) in 1978. Nicholson, also under con-
tract with DPS, walked transects in Ward Valley in 1978 to
determine approximate tortoise densities.
STUDY AREA
Location. The study site is located in Ward Valley,
San Bernardino County, 32 km east-southeast of Essex (off
Interstate Highway 40) and 34 km southwest of Needles (Fig-
ure 1) . It is located in T 7N and R 20E on the Stepladder
Mts. 15' topographical map and extends from the western
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Figure 1. Location of Ward Valley study site.
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border of S28 to the eastern border of S27 and from 0.3 km
south of the northern limits of these sections to 1.1 km
south. Rock cairns mark the plot corners.
Habitat . The site is situated on a bajada with a
westerly slope of 2.3% and an average elevation of 646 m
(2120 feet) . Granitic and basaltic rock hills in the
southwest corner of S28 and the northeast corner of S27 rise
49 m above the plain with slopes of 24-73% (Appendicies V and
XIV. Gently rolling hills extend easterly from the rock
outcrop in S28 for 0.9 km; steeply rolling hills extend
westerly and southerly from the rock outcrop in S27 for
0.6 km and easterly, past the plot, for 3.2 km.
Three wide (20 to 150 m) , east - southeast to west-
northwest, sandy washes, replete with small islands in
several portions, transect the plot. One lies in the south-
western one-third of S28 and two are in the eastern one-half
of S27. The northern border of the plot in S28 and the
southern one-half of the plot, from the rolling hills in the
east to those in the west, is replete with shallow (banks
less than 10 cm high), narrow (0.5 to 2 m wide) watercourses.
With the exception of the rock outcrops, slightly hard
(consistence when dry) coarse-sandy loam (U.S. p. A., 1960)
covers the surface. Decomposed granite is added in the roll-
ing hills, along with many granitic and basaltic boulders
and small rock outcrops. A few large (50 X 75 m ) patches
of desert pavement a present in the southeastern quarter
of S28.
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The flatter area primarily consists of a moderately
dense (plants separated by 0.5 to 2 m) Ambrosia dumosa - Lar-
rea tridentata community with Yucca schidigera (App. XIV) .
Volume decreases but diversity increases in the rolling
hills to include Er iogonum f asciculatum, Opuntia acantho-
carpa , Ence lia f arinosa , E. virginensis , Dalea Fremontii ,
Eriogonum inf latum, Ferocactus acanthodes and Machaer anth-
era tort if olia . However, Ence lia f arinosa is predominant
on the west-facing slope of the large rock outcrop in S27.
In the large rock outcrops, the community changes radically
to consist primarily of Nicotiana trigonophylla, Bacc haris
brachyphy 11a , P h y s a lj s cr assif olia , Hof meister ia pluri-
seta and Haplopappus Gooddingii .
Shrubs are largest and most dense in the areas of
greatest runoff and Fouquieria splendens , Acacia Greggii ,
Salazaria mexicana and Cassia armata are common in the
large washes (App. XIV). Where the ground is replete with tank
tracks, dwarfed Lar rea tridentata is the sole perennial.
The understory is dominated by Pectocarya spp.»
Cryptantha spp . are subdominant on the flats. The di-
versity of annuals is excellent, and common species
include Lotus tomentellus , P lantago insular is , Schismus sp.
Bromus rubens , Chorizanthe spp. , Lepidium lasciocarpum, Les-
querella Palmeri , Streptanthella longirostris , Chaenactis
spp. and Eriogonum spp. By casual observation, it seemed
t.o me that L. tomentellus is most dense and possibly sub-
dominant along the western border of the plot.
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Wind generally issued from the south-southeast through
the west and from the north. Speeds averaged 3 . 6 mps (8 miles
per hour) with 10 days of windspeeds greater than 8.9mps (20
mph) . Rain occurred on 1, 23, 28, 29 and 30 April and
1, 10 and 22 May. Total rainfall during the study was
70.6 mm (this figure taken from the United States Climato-
logical Survey for Needles). Air temperature maxima and
minima were averaged from tortoise data forms for March
through May and were measured at sunrise and midday during
June (Table I) . March lows could not be determined due
to insufficient data.
)
Table I. Average air temperature maxima and minima and
change in day length for the duration of the study.
Month
T
air
Min imum
(°C)
Maximum
Day Leng
Sunrise
th (PST)
Sunset
March
April
May
June
Undetermined
18. 6
16.9
19. 6
19. 3
22. 3
~29.0
35.4
-0520
^0510
0500
0448
^1740
'-I 800
1818
1840
)
Human Inf luence . The study area receives very little
vehicular use. A rarely- travel led , dirt pipeline road tra-
vels east to west, 1 km north of the plot. A well-hidden
and disused jeep trail extends from this road through the
plot center. Two sets of 4WD tracks, fresh this spring,
were present in one wash.
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Many tank tracks from Army maneuvers in 1942 (Blumenson,
1972) and the 1960*s crisscross the northwest corner of S27
and part of the northeast corner of S28 (Appendix XIV). The
paucity and stunted habit of the perennial veqetation indi-
cates severe destruction of the shrub layer by maneuvers.
Annuals have revegetated the tracks and if it weren't for
the lack of regrowth of the ubiquitous, soi 1 -encrust ing ,
black lichen, the tracks would be difficult to distinguish
in many instances.
METHODS AND MATERIALS
)
Tortoises were sought for 60 days (64 person-days) from
24 March to 14 April, 23 April to 11 May, 22 to 26 May, 1
to 4 June and 6 to 15 June. Searching hours were ca: a) 0800
to 1700 h (PST) for March and early April (9 hours); b) 0700
to 1200 h and 1330 to 1815 h for late April and early May
(9 - 10 hours); and c) 0515 to 1130 h and 1500 to 1900 for
late May and June (9.5 hours).
The plot was covered by systematically walking short
transects, ca 0.2 km in length and spaced ca 10 m apart
(that distance determined by vegetational density) . Ulti-
mately they covered a rectangular section of the plot, the
width of which was determined by the time allocated to search
ing each day and the number of tortoises found (it required
ca 20 minutes to examine a new capture). This method was
felt to be most effective because (1) it was unlikely that a
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tortoise would travel so quickly as to avoid being sighted
either on the forward or return transect; the short transect
length encouraged rapid return by the researcher^ and (2) it
enabled the researcher to view an area from various angles.
To avoid duplicate searching, the daily area covered was
mapped. Flagging of tall perennials every 0.1 km and the
mapping of landmarks, plus a topographical map assisted in
the accuracy of determining locations. The plot was covered
slightly more than two times during the 60-day period.
Upon discovery of a tortoise, it was initially ob-
served without disturbance, when possible, to determine be-
havior. Subsequently, several measurements were taken and
recorded on forms provided by the BLM (Appendix VI). The
first measurement taken (in an effort to obtain an accurate
measurement prior to the tortoise's voiding) was the weight
of the individual, determined by placing the tortoise in a
metal pie pan and supporting this in a nylon net attached to
a 6 kg Chatillion or 100 or 300 g Pesola scale. If the tor-
toise voided, the amount, color, viscosity and presence of
insolubilities were noted. In addition to weighing the
tortoise, the following measurements were taken, using
Brown and Sharpe calipers: maximum carapace length (MCL);
width a marginals 3 (posterior), 4 (middle) and 7-6
(seam); greatest width and its location; height at mid-
central 3; plastron length from notch to notch (PL N) ;
and maximum plastron length (PL T) . Care was taken to leave
the tortoise on its carapace for minimal periods as its
breathing appeared to be labored in this position and because
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the chance of causing torsional problems (intestinal twist-
ing) was decreased (Berry, personal communication). Evidence
of parasites or new growth was noted and the growth rings
were counted. In addition, the sex was noted (for indivi-
duals over ca 180mm MCL) and the gular condition and shell
wear were described and drawn. Injuries and anomalies
were described, drawn and photographed. Photographs were
also taken of the carapace and left costals 3 and 4. I
would like to suggest that photographs also be taken of
the plastron in future studies as individual differences
are very distinct here. Behaviors before, during and
after handling, were recorded. Temperatures were taken
with a Schultheis thermometer, the bulb of which was manually
shaded, one meter above the ground (T ) , one centimeter a-
bove the ground (T-[cm) and on the ground surface (TgS) .
Cloud cover, wind direction and wind' speed (the latter
using the Beaufort technique) were recorded. The location
of the tortoise was noted and mapped (Appendix I). Finally,
each tortoise was consecutively numbered by notching in
accordance with the Desert Tortoise Council notching sys-
tem (Appendix VI 1 1) . In addition, the number was drawn on
the anterior and posterior portions of the carapace with a
waterproof; felt-tip marker to enable the investigator to
identify an unobtainable tortoise in a burrow.
After releasing a tortoise, the immediate vicinity
within a radius of 50m was searched in order to locate the
tortoise's burrow or pallet. (This procedure was reversed
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if a fresh burrow or pallet was located prior to observing
a tortoise.) Length of the burrow and two lengths for a
pallet, one from the interior end to the edge of the overhang
and the second from the overhang edge to the end of the " a -
pron", were measured. Height, width, soil cover, vegetal
cover, direction, slope, co-occupants, curvature (determin-
ed with the aid of a mirror) and the distance and direction
from the tortoise were also recorded, length measurements
being taken with a collapsible pole and a tape measure.
The burrow or pallet was then marked with a rock cairn to
aid in identification when observing future use.
Upon recapturing a tortoise, mapping and measuring
for weight and MCL were repeated in order to observe changes.
Additionally, presence of new growth, parasites and behavior
were observed.
All shells or parts encountered were photographed in
situ and collected subsequent to searching the area within
several meters of the initial discovery for all remains.
Shells were labeled (number, site, date, principal investi-
gator's name) and, if possible, measured with respect to
plastron and carapace lengths, widths at marginals 3-4, 7-8
and the point of greatest width. Sex, possible mortality
factors, condition of the skeleton and scutes, and the lo-
cation of the remains were noted. All data were recorded
on forms provided by the BLM (Appendix VII ) and the speci-
fic location of the ^hell was mapped (Appendix II).
The belt transect method, suggested by the BLM, was
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used to sample vegetation. Perennial vegetation was sampled
along two permanent transect lines (marked by large rock
cairns at each terminal corner) through homogeneous vegetal
communities on 8 and 9 April and 12 June. Annual vegetation
was sampled between the 1st and 5th of both April and May;
13 samples along each perennial transect line were taken
each month.
All mammalian predators and raptors and their sign
were noted and mapped. All predator scat were examined
for tortoise remains.
RESULTS AND DISCUSSION
Population Parameters
Density . One hundred forty-two tortoises were cap-
tured. This figure is undoubtedly less than the actual
density due to tortoise mobility and obscured visibility,
especially for tortoises under 100mm MCL (Karl, 1979a;
Burge, 1977b; Grubb, 1971 ). Only half of
the subadults and adults were recaptured at least one
time, which indicates, according to Fitch (1967), that
many members of the population were yet to be captured.
Although the proportion of recaptures to total captures
increased in each daily census as the study progressed,
it was only 0.77 by the end of the study (Figure 2).
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If the curve of absolute density is extended (by estimation)
to the point where recaptures equal captures, then the popu-
lation estimate is 59 to 64 tortoises per square kilome-
2
ter (150 to 165 tortoises/mile ).
20CX
Curve A-Total
number of tor-
toises marked
to interval
Curve B- R:T X
100 for inter-
val
150.
100
Est imated
Cone lusion
Y = 5. 2 X + 9.9
15 10 15 18
Consecutive 5-day intervals
Figure 2. Progressive proportion of recaptures (R) to
total daily captures (T) for consecutive 5-day intervals
during the study period (curve B) compard to absolute
density increase per consecutive interval (curve A).
As the plot was covered only twice, a standard mark-
recapture calculation (e.g. Lincoln Index; Marten Regres-
sion Method, 1970; Hayne modified Lincoln Index, 1949)
could not be applied. However, a Schnabel (1938) calcula-
tion, which uses cumulative, daily population estimates and
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is unaffected by day to day fluctuation in searching (e.g.
number of hours worked, reduction of tortoise activity due
to inclement weather) on a short-term basis, indicated a
2
population density of 67 to 77 tortoises/km (= 175 to
200 tortoises/mi2). A basic assumption of the Schnabel
computation is that random stations are resampled several
times. On the tortoise plot, this was not true. New areas
were searched daily, resulting in a low proportion of re-
captures to total daily captures and a resultant high es-
timate of the population density. A more appropriate method
of sampling the plot would be to randomly (to compensate
for clumping) sample small areas on the study site several
times apiece.
Another factor which would influence the population
estimate would be the number of unmarked tortoises found
near the border during the final days of the study, due to
immigration from uncensused areas outside the plot. This
would decrease the recapture to total daily capture ratio,
thus increasing the density estimate. Sixteen new tor-
toises were found from 1 June to 15 June; 11 (68.8%) were
found within 200m of the border. The time spent searching
the border area was approximately equal to that nearer the
plot center (although ca one-third of the latter area was
in low-density portions of the plot). The upper limit of
the computed density estimate is probably slightly high
as a result. The final density estimate, combining all fac-
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1 3
^
2 2
tors is ca 63 tortoises/km (= 160 tortoises/mi ) . Berry
(personal communication) estimated the density at 39 tor-
2 , .2,
toises/km (= 100 tortoises/mi ) .
The rocky and foothill areas cover ca 35% of the
plot. If tortoise density there is equal to that on the
flat areas, then 35% of all captures should have been here;
instead, only 17% occurred here. Density on the flat area
(«*fivich extends several miles to the north and west) is ca
77 tortoises/km . In the rolling hills (which extend a
few miles to the east of the plot) , the density is esti-
2 2
mated at 31 tortoises/km (= 80 tortoises/nu ) .
Distribution. Tortoise sign was moderately low in the
foothills and extremely low in the boulder outcrops. Only
the scat of three tortoises plus two tortoises and two
burrows (one with a tortoise) were found in the latter area
Reasons for the lack of tortoises in the hilly areas in-
clude
1) Fewer tortoises were found than were actually pre-
sent due to obscured visibility and difficulty of
walking in the rocks. However, searching lines were
closer than normal (3-5 m apart) and searching was
accomplished during hours of tortoise activity to
compensate for these difficulties.
2) Burrowing potential in the hills is generally poor.
The soil is denser than on the flats and often over-
lays boulders. In the rock outcrops, burrowing is
impossible and coversites can only be provided
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14
")
by overlapping rocks; two such burrows were found.
Burge (1979) suggested that tortoise densities were
higher in rocky outcrops than on the surrounding
flats in a section of Arizona because there were
many coversites provided by boulders. Although the
soil on the flats was friable, burrowing into the
soil was apparently unpreferred to finding cover
in the rocks, this despite the fact that tortoises'
front legs are specialized for digging (Pritchard/
1979). Aside from burrowing potential, nesting
potential (generally observed as involving dig-
ging) in the hills is low. Pritchard (1979) noted
that a population limiting factor is the availa-
bility of suitable soil for nesting.
A thermoregulatory advantage is gained by
burrowing into the soil rather than finding shel-'
ter under rocks (not including deep caves) during hot
weather. McGinnis and Voight (1971) stated that
the burrow is the only shelter with non-lethal
temperatures during hot days. However, they did
not sample rock caves.
3) Forage availability is decreased in the rock out-
crops over than on the rolling hills and flats.
Between the latter two, annual vegetation is simi-
lar and the difference in perennial composition is
not relevant with regard to forage. However, few
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annuals are available in the rock outcrops and there
is no record available that the perennial? there con-
stitute tortoise forage.
4) Moving among rocks expends more energy than moving
along flat ground.
It would seem, then, that the benefits derived from living
among the rocks and, to a lesser extent, in the rolling
hills are few .
Sex Ratio and Age Structure. The sex ratio indicates a
large majority of males (Table II) . Several researchers have
indicated that most reptilian populations have adult sex ra-
tios nearing 1:1, but with a female predominance, sometimes
as high as 4:1 (Tinkle, 1961). Tinkle (1967) quoted a 55:45
sex ratio, in favor of females, for U ta s tansbur iana . Swing-
land and Lessells (1979) observed that there was a slight
differential mortality in males, resulting in an adult sex
ratio in Geoc he lone gigan tea Schweigger of 1 male: 1.6 fe-
males. Berry (1976) estimated that healthy populations of
Gopher us agassizi must not have a predominance of males.
An equal sex ratio at hatching has been recorded by
Tinkle (1967) for Uta stansbur iana and Swingland and Coe
(1979) for G. gigantea . Rohlf and Sokal (1969) offered a
range of 1 male : 0.64 females to 1 : 1.59. Tinkle (1961)
observed that in one large sample of young S ternothaerus
odora tus hatchlings showed slightly more than a 2:1 ratio
in favor of females. If the sex ratio of G. agassizi
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Table II. Sex ratio of live tortoises
Method of Determin-
ing Age Class
Age
Class
Num
?
ber
Ratio
By Carapace Length
Subadul t
Adult
8
23
9
42
0.88?? : lo"
0.55 : 1
By Shell Wear *
Subadult
Adult
3
28
5
46
0.60 : 1
0.61 : 1
* Obtained from Karl (1979a)
hatchlings was also 1:1, then differential mortality must
occur for females at the Ward Valley study site, assuming
very good sampling. However, Yntema (1976) showed that a
change in nest temperature^ during critical incubational de-
velopment, of as little as 2°C was sufficient to significant-
ly alter the sex ratio of hatchlings for Chelydra serpen-
t_i_na . Year to year variation in weather could influence
the nest temperatures. Data for nest temperatures relative
to hatchling sex ratio is not available for G. agassizi ,
so it is difficult to determine if differential sexual mor-
tality actually exists.
This population has a high percentage of tortoises under
100 mm MCL, 24.6% (Table III), and, in view of the fact that
23 of the 27 Immatures are under 135 mm MCL (Figure 3), a high
percentage of young Immatures. Berry (1976) indicated that in
an undisturbed population, 1-3% of the total population should
be less than 60 mm MCL, 5-10% Juvenile II's (i.e. 6-13% under
100 mm), 15-20% Immatures, 15-20% Subadults and 45-60% adults.
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The high reproduction in Ward V. would indicate that carry
ing capacity has yet to be reached. Probably at least one
clutch is laid yearly as Swingland and Coe (1978) suggest
that breeding or multiple clutches are density related in
Geoche lone gigantea.
Table III. Age class structure of live tortoi
ses
Size
■
Class
Number
Percentage of
Adult : Non-adult
the Population
Ha tchling
( no ring )
A
2.8
84 : 100
Juvenile I
(^1 ring,
4
2. 8
to 60mm MCL)
Juvenile I I
(61-100mm)
27
19.0
Immature
(101-1 79mm)
25
17.6
Subadul t
(180-207mm)
17
12.0
Adult
(*207mm)
65
45.8
Total
142
100.0
There is not a high percentage of adult females, so the
high reproduction is surprising. Possibly, optimum environ-
mental conditions have overridden this reproduct i ve ly sub-op-
timum sex ratio. Rainfall, which is direct iona 1 ly propor-
tional to forage production, has been positively correlated
to reproduction rates for several species of lizards (Turner,
Medica and Smith, 1973; Mayhew, 1966a and b, 1967; Vinegar,
1975; Zwiefel and Lowe, 1966). Swinqland and Coe (1978)
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18
MCL
(mm)
290-
280-
?
3
<?
270-
260-
i
2 50"
m
240"
> 230-
i
220-
210-
i
I
,
—
200-
190-
|
175-
r i i
Undetermined
Sex*
160«
150.
140-
•
130.
120«
I
110'
i
1001
i- .. ...
90
i
80
70'
■
,
60
i
I
5 0
45
i
1 • 1 t 1 > 1
10 98 765 432 101 12 34 56789 10
Number of tortoises
Figure 3. age structure of live tortoises in MCL increments
of 5mm. * = The number of tortoises for each increment is
shown on one side of central line.
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19.
showed that the most important factor influencing annual re-
production in Geoche lone gigantea is rainfall. Increased
rainfall results in reduced follicular atresia and increased
oviposition or egg mass. Although Pianka (1970) agreed that
clutch size in several species of lizards is positively cor-
related to rainfall, he suggested that biotic (predation, comp-
etition) rather than climatic factors are more influential in
low elevation populations (which would include this site) .
If an attempt is made to correlate the age structure
of this population to rainfall, one would expect high re-
production 6.5, 1.5 and 0.5 years ago due to high winter
rainfalls 7,2 and 1 years ago (Fig. 4) , according to figures
recorded for Needles, CA (elevation 141 m). (Although these
figures might not equal those of the study site, they probably
indicate a precipitation trend). It is also possible that
heavy summer rains prior to winters of low rainfall might
sitmulate increased oviposition the following spring.
Hahn and Tinkle (1964) observed that Uta stansbur iana es-
sentially used none of the fat bodies accumulated prior to
hibernation for winter survival. Upon emergence from hi-
bernation, high fat body content provided material support
for follicle yolking at a time (early sprinq) when food
availability was poor. If Gopherus aga ss izi behaved similar-
ly, entering hibernation with good fat reserves from high
availability of winter annuals following summer rains, then
hatching would have been high 2.5 and 4.5 years ago (Fig. 5).
f
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Rain
(mm )
17 5J
I
150j
125j
iooi
7S
50
2S
20
"1
OiO<H<Nro'3,ir»vDr»ooCT*0<-i{Nro'3,invDr^cr)(TiO
i i i i i i i _-i _- * i «i _J _J ■— I ■— ^ #— 1 i— i i — ( t—4 i— ( — i
00 <Ji o
01
I I I I 1 I I I I I I I I I I I I I I I I I I
r^coc^Or-i<Nni3'in^Dr-oooNOrHCNro^rinvDr^ooCTv
inininvOvDvovDvDvD<x>OvDvDf,~r«-r,~r^r~r,-r>-t~»r»f%»
plHHrlHHHHHHrlHrlrlrlHHHrlrlHHH
Winter
Figure 4. Winter rainfall (October through April)
at Needles, CA from 1957 to 1980.
250T
225
200
175
150
Rain
(mm) 125
100
75
50
25 J
0
co cri o h (N n f invor^ co ff> OrHCNro^rmvor^oocyi
cftCftcr>cxicriCftCTicricricr!C^c> cric^cxicyiexicyicrvcriCTicri
, — | ^— | ,>— I . — I r-l.Hi-li-lr-lr-l.-lrH rH rH ,HrH.HrH.HrHrH.H
Year
Figure 5. Yearly rainfall for Needles, CA
from 1958 to 1979.
f
<
t
21
Using carapace length ranges for various ages provided
by Patterson and Brattstrom (1972) , Miller (1955) and Alt-
mann and Dittmar (1962), all tortoises under 120mm MCL
could fit into one of the age categories specified by high
rainfall. Rainfall was lower than average between 11 and 14
years ago and there are only four tortoises in this age cate-
gory. However, rainfall was also low 7 to 10 years ago and
there is a high percentage of tortoises this age (120 to 135mm
MCL) . The descrepancy may be attributable to the difficulty
of assigning carapace length to a specific age. Rainfall may
not be primarily responsible for increased production of
tortoises; however, there is a logical correlation between
high food availability (due to timely and sufficient rainfall)
and high reproductive success.
Reproductive Potential . The size structure of this pop-
ulation shows that most of the large tortoises are of repro-
ductive size and that the percentage of adults, 45.8%, is not
too low for healthy reproduction, according to Berry (1976).
Also, 61% of the adult females and 61.9% of the adult males
were probably in their prime as they showed relatively little
shell wear (i.e. distinct rings, no scute sinking, no seam
widening). Only 21.4% of the females and 10.9% of the males
were presumably old (i.e. scutes sunk on carapace and along
midline; wide, deep sutures; smooth marginals' edges). Re-
productive senescer ce has been observed in a few species of
turtles (Legler, I960; Gibbons, 1969; Cagle, 1944, Tinkle,
22.
1961). However, Swingland et al (1979) observed no senes-
cence in Geoche lone gigantea . It is not known what percent-
age of a healthy Gopherus agassizi population normally com-
prises old individuals; however, the percentages here seem
small .
Morta 1 i ty . Seventeen entire, shells or large fragment
groups representing one tortoise each, plus 31 small groups
of isolated fragments, were found. The highest recovery
occurred in adult tortoises (Table IV) . when expressed as
the percentage of live tortoises found in each size category,
the mortality was slightly higher in subadults (17.6%) than
in adults (13.8%). The result that there were no shells under
60mm MCL is probably due to low mortality, although lack of
ossification of the shell (Berry, personal communication),
reduced visibility and complete devouring by predators
could also alter shell recovery results.
Table IV. Tortoise skeletal remains.
Size
Class
Sex
Und. ? d*
Total
% of
Total
Dead : Live
Tortoises
Hatchl ing
Juveni le I
Juveni le II
Immature
Subadul t
Adult
0 0 0
0 0 0
2 0 0
2 0 0
0 2 1
1
3 15
0
0
2
2
3
1
9
0.0
0. 0
11. 8
11. 8
17.6
5.9
52.9
0. 0
0.0
0.07
0. 08
0. 176
0. 138
Total
7 3 6
17
100. 0
\
23
The shell wear scheme used to determine approximate age
since death, presented by Luckenbach (1976), showed that of
the 17 dead tortoises 2 were deceased within the last year,
1 died ca 1 year ago, 3 died 1 to 2 years ago, 1 died 2 years
ago and 10 died between 2 and 5 years ago. This results in
an annual mortality of 3.4 tortoises (= 2.1%/year). Exposure
to the sun decayed shells more rapidly. One shell with solid,
but slightly peeling and chipping bones and peeling, faded and
loosened scutes had been present at least one year, indicated
by the conformational growth of last year's annuals to the
shell shape.
Bones were more or less white with brown or black stains
and occasionally a pinkish cast. Pink interiors were observ-
ed in newly disjointed sutures. In juvenile tortoises, the
sutures were black-brown.
Small sample sizes precluded forming conclusions regard-
ing differential sexual mortality.
Twelve non-crumbling skeletal groups, representing all
age classes, were broken, possibly indicating predation, although
tooth marks were'nt evident. Five shells were chewed, although
the cause of death in two, an adult and an immature, was
uncertain as the tooth marks were on the shell periphery
on one and on a scute but not on the underlying bone in the
other. Of the remaining three tortoises, one, a Juvenile I,
was chewed and crushed over the entire one-third of the cara-
pace; the second, a Juvenile II, was found in a canid scat;
and the third, a Juvenile II or Immature, had punctures in
(
(
24.
an abdominal scute. Two tortoises were found upside down and
possibly died of exposure and one Juvenile II was slightly
flattened with a broken Vertebral I, possibly due to vehicle
or cow crushing (although there was only slight evidence of
non-recent livestock grazing) .
Mammalian predators at the site included kit foxes (Vul-
Pes macrotis) , coyotes (Canis latrans) and bobcats (Lynx ru-
fus) . The latter two were sighted and the first was evident
by the presence of scat, burrows and excavations. It is
probable that the gray fox (Urocyon cinereoargenteus) and
the badger (Taxidea taxus) were also present as their ranges
extend into Ward V.
Raptors included Burrowing Owls (Speotyto cunicularia)
Red-tailed Hawks (Buteo jamaicensis) , Golden Eagles (Aquila
chrysaetos) and an unidentified buteo. Although not sighted,
the ranges of the Great Horned Owl (Bubo virginianus)
Swainson's Hawk (Buteo swainsoni) , Ferruginous Hawk (B. re-
ga_l_is_) and Prairie Falcon (Falco mexicanus) extend into the
study area. Ravens (Corvus corax) were also present during
the study and have been reported as predators of young tor-
toises (Woodbury and Hardy, 1948).
Predators influence shell recovery results as they carry
shells away from their original locations (Luckenbach, 1976)
or devour them completely. The number of incomplete shells
may attest either to predator influence or collection by Ra-
vens (Peterson, 1961) or woodrats (Neotoma sp.). Ten
(
c
25..
tortoise remains were found in woodrat nests.
Injuries and Disease. Thirteen to seventeen live tor-
toises had chew marks (e.g. punctures, ragged edges). These
occurred primarily on the periphery of the shell. However,
one soft tortoise, 80mm MCL, had many punctures along the
plastron midline and on one opposing vertebral. One subadult
tortoise's forefoot was mangled as well as its shell being
chewed. Only three of the chewed tortoises were small, 118,
96 and 80mm MCL.
Eleven tortoises had deep incisions or chips to the bone;
on one of these, the chipping was extensive. The side of
one tortoise was compressed and deformed. One tortoise had
lost the tip of its tail and one had a blackened, deformed
toenail. The gular tips were broken off in seven adults,
six of which were males.
"One old male breathed audibly. The sutures of one,
possibly diseased tortoise all exposed bone and another,
also possibly diseased tortoise, had indentations with ex-
tensive peeling over much of its shell.
Parasites. Ticks, 1.5 to 3.5mm in length, were para-
sitic on 49 tortoises. Most of the tortoises were Adults,
77.6%; the remainder were Subadults, 18.4%, and Immatures,
6.1%. All of the old tortoises possessed ticks. Ticks
numbered from 1 to 100 and were primarily attached to the
posterior carapace (100% of the observations) , although
in 14% they were also on the anterior carapace. Only one
tick was not on the carapace; it was attached to the dor-
(
{
26
)
>
>
sal surface of the gulars. Sites of attachment were generally
scute sutures (83.7%), although they were also attached to
scute centers (45.1%) and in deep chips or exposed bone. The
presence of the latter or of new growth did not necessarily
stimulate parasite attachment at that site. Of 88 tortoises
with new growth, only 28.4% had ticks and only 51.0% of all
parasitized tortoises had new growth. Grant (1936), Har-
bison (1937) and Woodbury and Hardy (1948) noted that ticks
attached to shell sutures, exposed bone and soft skin, possi-
bly due to ease of access to the blood supply. No ticks were
observed attached to skin during the present study.
Shell Wear. Chipping of the keratinous layer was the
prevalent form of shell wear, observed in 80 (56.3%) tortoises;
in 31 of these, chips exposed bone. In 35 tortoises (24.6%)
there were hairline cracks, most often extending from the plas-
tral midline. Other shell wear included extensive peeling
(5 tortoises) and "bubbling" under the shell surface (7 tor-
toises) .
Anomalies . The prevalent "anomalies" included sutures
not meeting at the plastral midline (77.3% of all tortoises);
pronounced or mottled coloration (67.9%); curves in sutures
(83.9%), especially between the vertebrals (35.0%), along
the midline (25.5%) and in the anterior pectorals (17.5%);
slight to extreme posterior flaring (65.7%); misshappen
scutes, such as assymetr ical , fused, under- or oversized
or overlapping (46.0%); oval shape (21.9%); and prominent
scute centers (21.2%). The remaining anomalies, each pre-
(
c
27
sent in less than 13% of all tortoises, included various
shapes, viewed dorsally, indentations in marginals 5 and 8,
upturned anterior flares, extra or reduced numbers of mar-
ginals or costals, recessed or missing nuchal, deformed
toenails, scattered lumps of keratin, different eye colora-
tion in the same tortoise, irregularly notched nuchal or
pygal and prominent diagonal "foldlines" formed by the
corner points of the growth rings and especially prevalent
on costal 3 and the pectorals. There was no correlation
between tortoise size and most anomalies except that poster-
ior flaring was less pronounced in very young tortoises
and the majority of these were richly colored. Also,
prominent scute centers were primarily observed in sub-
adult and adult tortoises.
Sexual Differentiation. Females generally had a
prominent pygal tip (Figure 6). Of 23 females, from 176
to 230mm MCL, inspected for this feature, all had prominent
pygal tips. Of 30 males examined, 26 had prominent areas
at the Vertebral 5/pygal suture or above, but the tip of the
pygal pointed straight down or was tucked slightly under.
Four males had prominent pygal tips, although in three of
these the prominence was slight. This feature might be used
to determine sex in tortoises under 180mm MCL as both forms
were observed in four inspected tortoises as small as 121mm
MCL. It could also assist in determining the sex of incom-
plete skeletal remains when at least the posterior carapace
is present.
r
(
c
28
?
Figure 6. Sexual differences in the posterior carapace
viewed laterally.
Growth. There were only Six: tortoises under 180mm MCL
for which growth (expressed as the percentage of MCL change
and the percentage of weight change) could be examined.
One 53.3mm MCL tortoise exhibited the greatest growth rate,
increasing 0.38%/day in length from 1 April to 14 June (= 13mm
in 64 days) and 1.84%/day in weight (= 40g). The remaining
five immature tortoises averaged slightly greater length
gain but approximately equal weight gain to that of tortoises
over 180mm MCL (Figure 7). It has been shown for several tur-
tle species that growth is rapid in young individuals, de-
creasing steadily to sexual maturity, at which point it be-
comes slow (Gibbons, 1967; Graham, 1971; Heatwole, 1976; Me-
dica; Bury and Turner, 1975; Moll, 1973 and 1976; Patterson
et al, 1972? Swingland et al, 1979). A 185 mm female exhibit-
ed the second greates gain in weight, 0.92%/day (= 350 g) in
28 days. A 253 mm tortoise gained 0.04% (= 15 g) in only
4 days; however, a 254 mm tortoise gained no weight in 6 days.
r
(
c
2 9.,
No increments -100g (unless recorded by the Pesola scales) or
lmm were considered due to inaccuracy of the measuring devices
>.
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m
M
a
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JZ
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0.5 0. 1-
i i' « ■
o C". r- r-
\£» r- o O
V i-H CM CN
l i *
r-\ O
O CO
fH rH
MCL (mm)
Figure 7. Average length (•) and weight (+) gain for
each size group. Vertical lines represent standard de
viat ion .
r
(
(
3,0.
The growth rate in length was 0.033%/day (= an average of
6.5mm in 82 days [Medica et al, 1975, found that growth occurred
primarily in 82 days between 15 April and 6 July]) greater in
adult males than in adult females (Table V). Swingland et al
(1979) also observed faster growth for male than for female
Geochelone gigan tea . There was no sexual difference in a-
dult weight gain (Table VI), possibly because the greater
gain in length (probably accompanied by a weight gain) in
males was equalled by a weight gain in females for developing
follicles. There was no sexual difference in length gain
between four subadult females and four subadult males; how-
ever, eight subadult females averaged a weight qain of O.D%/day (=
157g in 82 days) more than the average of six subadult males.
Table V. Percentage of MCL change per day.
Sex
Size
Class
(mm)
Average
MCL (mm)
Average %
Change/Day
Standard
Deviation
Range
N
d"
> 207
180-207
> 207
242
196
218
0.040
0. 080
0. 007
0.20
0.05
0.06
0-0. 15
0-0. 12
0-0.003
13
4
9
?
180-207
101-179
101-179
192
175
164
0.090
0. 130
0.090
0.06
0.03
0. 06
0-0. 14
0. 11-0. 15
0. 04-0. 12
4
2
3
Und
< 60
53. 5
0. 380
1
Three periods of time were used to determine if growth
rate changed during the spring season. These were: (a) Group
I - ca 1 April to 5 May, with an average of 29 days; (b) Group
II - ca 1 May to 15 June, with an average of 23 days; and (c)
(
(
<
31,
Table VI. Percentage of weight change per day.
Sex
Size
Class
(mm)
Average
Weight
(g)
Average %
Change/Day
Standard
Deviation
Range
N
i
>207
180-207
>207
3200
1660
2072
0.14
0.23
0.14
0.13
0. 14
0. 10
0-0.47
0-0. 39
0-0.32
31
6
11
?
180-207
101-179
101-179
1477
1385
467
0.36
0. 18
0. 31
0. 27
0.18
0. 20
0-0. 92
0. 05-0. 31
0-0. 41
8
2
4
Und
<60
34
1.84
1
>
)
Group III - included at least one-half of both groups I and
II, with an average of 66 days. Groups I and II could not be
compared directly with regard to length gain because there
were no tortoises in Group I except for adult females (Table
VII). However, the length growth rate was 0.01%/day (= 1.8mm
for 82 days) greater for one Group I, adult female than for
three Group II, adult females. With regard to weight gain,
sample sizes are small in groups I and II, with the exception
of adult males, and the results are inconsistent (Table VIII).
For adult males, there was little difference between groups
I and II. The Group III totals were larger than either Group
I or II totals, possibly due primarily to the very large,
Group III growth rates for one juvenile II tortoise. The de-
letion of the rates for this tortoise reduces the Group III
rates to 0.05%/day for length and 0.21%/day for weight; these
figures approach those for groups I and II. If the growth rate
was irregular during spring, one would expect a difference be-
tween groups I and II with an approximate average in Group III
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)
As this was not observed, there is probably no intraseason vari-
ation in growth rate (although large standard deviations indi-
cate the difficulty of forming conclusions). Medica et al
(1975) stated that length growth rate was greatest in the lat-
ter part of the season. Maximum primary production this spring
in Ward V. occurred during the Group I time period. It is
tempting to speculate that the increased weight gain rate for
Group I, adult females is due to developing follicles.
Growth rates reported here are for a spring following
a winter of high rainfall (Figure 4). Growth would probably
be less during springs of low primary production, following
winters of low and/or untimely rainfall.
Woodbury and Hardy (1948) noted that it is difficult to
assign age to a tortoise by counting growth rings. Probably
only one ring is added in a spring, but an additional ring
may be added in the fall, especially if there is high pro-
duction of winter annuals. In mature tortoises, the rings
become rubbed and indistinct. Figure 8 shows the approximate
size of young Ward V. tortoises compared. to their respective
number of rings. If one temporarily assumes that one ring e-
quals one year of age, then the agerMCL ratio does approximate
that given by Patterson et al (1972), Miller (1955) and Altmann
and Dittmar (1962). Thus young tortoises can be relatively
accurately aged by their growth rings.
New growth (lightened, flat area between scute sutures)
was first observed .n April and continued into June, the width
of the growth lines widening as the season progressed. How-
ever, fewer tortoises exhibited new growth in June (23) than
r
(
(
34
)
14 0i
130
120
110.
100
MCL
(mm)
90.
80 '
70
60
50
Y=5. 3X + 53.3
|i i i 1 ■ i i i i i ' i '■ i i ... .
0 1 2 3 4 5 6 7 8 9 30 II 12 13 14 15 16 17 18
Number of Rings
Figure 8. Growth rings for tortoises under 140mm MCL.
(
<
(
35
)
in May (45), indicating that growth slacked off in June.
These results are similar to those obtained by Medica et al
(1975) .
Behavior
)
Thermoregulation. Tortoises were active primarily between
ca 1030 and 1500 h during March, although basking was observed
as early as 0830 h, which might indicate earlier activity than
was observed (Fig. 9). Active tortoises were observed throughout
the day (0745 to 1700 h) in April, although several tortoises
were seen in retreat between 1100 and 1500 h. No searching
occurred between 1230 and 1500 in May and June, but active
tortoises were only sighted in the morning, from 0630 to 1200
in May and from 0545 to 1000 h in June, and in the late af-
ternoon, from 1500 to 1730 h in May and from 1600 to 1800 h
in June. Tortoises were found to be equally as active in the late
afternoon as in the morning.
Karl (1979b) concluded that ground surface temperature
(T ) is the most reliable indicator of tortoise activity
gs
because wind speeds >6.7 m/sec (=15mph) alter air tempera-
tures inconsistently. In Ward Valley, activity coincided
with T of ca 20 to 43°C, although two active tortoises
gs
were observed during T of 45 and 45.2°C. Tortoises be-
gs
gan retreat, however, at T greater than ca 35°C from April
g s
to June and were seen in retreat at T less than 25°C in
gs
May and 29°C in March. Tortoises which emerged for evening
activity did so at ca 38°C.
(
(
(
ae
)
>
»
June
Month
N
Active - 18
Basking - 4
Retreat - 22
nctive - 41
Basking - 14
Retreat - 16
Active - 51
Basking - 17
Re trea t - 16
Active - 8
Basking - 4
Retreat - 9
O O o o o
o o o o o
\C CD O (N *3"
O O t-i rH iH
i ■ i
o o
o o
VD 00
o
o
o
Time (PST)
Figure 9. Tortoise activity relative to time of day in March
through June. /\/\/\ represents active tortoises, |'.;:'^V':1 repre-
sents basking and | | represents retreat.
Many tortoises were active in windspeeds 8.9m/s (= 20 mph) .
Two tortoises were active during rain, although one burrowed
tortoise was also found during rain.
Two burrowed tortoises were observed in April and June
at T of 25.3 and 29.2°C at 0630 and 1048 h, respectively,
gs
Retreat at preferred activity times and temperatures may be
an indication that all tortoises are not active daily (Berry,
personal communication; Karl, 1979b).
Activity increased in April and May, 60.0% of all sighted
tortoises (n = 84) and 57.7% (n = 71) , respectively, over
that in March, 38.1% (n = 21). It decreased again in June,
40.9% (n = 44) .
Burrows may have been used more for midday retreats as
r
(
c
37
)
)
)
the season's heat increased. In June, 79% (n = 14) of the
midday coversites were burrows as opposed to epigean re-
treats; in May, 50% (n = 4); and in April, 25% (n = 12).
McGinnis and Voight (1971) stated that midday burrow retreats
are favored because burrows offer the only sublethal temp-
eratures on days when ambient temperatures exceed the criti-
cal maximum. The sample size for evening coversites was
even less, but 3 of 3, 7 of 9 and 7 of 8 evening coversites
were burrows in April, May and June, respectively. McGinnis
et al (1971) noted that burrows are used less frequently as
evening coversites as seasonable temperatures increase; tor-
toises using surface retreats in the evening start foraging
at lower body temperatures than those in burrows, resulting
in longer foraging time for the epigean-retreat tortoises.
There was no substantial difference in the lengths of
utilized burrows throughout the season. They averaged
0.38 m for April (n = 31) and May (n = 34), 0.46 m for March
(n = 15) and 0.64 m (n = 26) for June. Only 16 pallets
were found, 81% of these divided equally between April and
May. Burge (1978) noted that pallet use was increased in
April and May over March and June, but that the use of short-
er burrows occurred progressively from March through July.
Burrowing Behavior. With the exception of one burrow,
all surface slopes at the entrances to 94 burrows were -30° ,
with an average slope of 10°. The remaining burrow had an
entrance slope of 60°. Forty-five per cent (42) had slopes
at the burrow entrance (primarily caused by the mounding of
f
c
I
38
~)
)
)
the excavated dirt), but leveled inside. Several of these
sloped gently for several centimeters prior to leveling.
Burge (1978) noted that the slope changed primarily within
the first 40 cm. Karl (1979a, b) also reported gentle slopes,
primarily leveling inside. Only 16% (15) remained sloping
at the interior terminus, none showing a slope greater than
30° and none showing a steeper slope than that at the en-
trance. In 37% (35) , there was no slope whatsoever.
The average soil cover was 73,3mm (n = 96) . The gentle
slopes indicate that there was little increase in soil cover
at the interior terminus of most burrows.
Fourteen burrows were on islands or in the banks of
watercourses. Five of these were in wide washes with sub-
stantial runoff, two being dug into banks which were 0.5
to 1 m high. Only three of nineteen covers ites in the rolling
hills were merely spaces between boulders; the remaining
burrows here were dug into the soil. In the rock outcrops,
two coversites were found, one of which was a 0.7 X 0.7 m
cave and the other aim tunnel. Neither were dug into the
flooring (primarily rock) and both were accessible only by
tortuous climbing over loose granite on slopes of 20 to 40°.
Three burrows were dug under boulders, two were dug under
fallen logs and two were dug under Yucca schidigera stems.
One mature tortoise (only the tracks were seen) inhabited a
fresh kit fox complex and three tortoises occupied former
rabbit or kit fox forms (judging from the round shape, tall
(
(
(
39
)
)
height and steep slopes). One subadult tortoise further ex-
cavated a rodent burrow and four tortoises, 52.5 to 96mm MCL,
were found in old rodent burrows. Rodent holes were found
at the ends of two burrows, rodent scatwere found in three
and the remains of Neotoma middens found in four. Bury
(1973), Lowe (1964) and Karl (1979a) observed modification
of rodent or rabbit burrows by tortoises and the use of ro-
dent holes by small juvenile tortoises. Neotoma sp . moved
into three burrows that had been occupied by tortoises this
spring so the presence of Neotoma debris in an extant tor-
toise burrow may indicate that tortoises have re-occupied
former burrows rather than further excavating Neotoma bur-
rows .
Tortoises preferred to construct burrows or pallets
under shrubs. Of 96 burrows examined for location with re-
gard to shade or visual protection, 49% (47) were under
shrubs and in partial shade during the day. Those that were
not constructed under the overhang of any perennial vegetation,
but did receive some shade, constituted 19.8% (19) and those
that were under bushes and received total, continuous shade
totaled 15.6% (15). Only 15.6% were completely in the open.
There was no apparent increase in shaded sites with increas-
ingly hot temperatures during the season. Likewise, there
was no evident month to month change in burrow preference re-
garding the portion of the day during which the burrow was
shaded (for burrows which received partial daily shade).
These results are probably due to the thermal protection pro-
(
<
i
40
)
J
tection provided by the burrow interior, regardless of pro-
tective shade. McGinnis et al (1971) showed that the air
temperature 1 m inside a tortoise burrow (the location of
which was not stated) during late May changed little during
the day . Their measurements indicate that shade is of little
importance relative to burrow temperature (for burrows of
adequate depth) and is thus not a factor in burrow site
choice (although Burge , 1978, suggested that it was). Possi-
bly the soil is looser under shrubs due to water retention,
notwithstanding the visual obscurity provided.
The species of perennial vegetation over 62 burrows was
examined. The predominant cover species was Larrea triden-
tata (56.5%), followed by Ambrosia dumosa (29.0%) , Yucca
schidigera (17.7%) and Krameria Grayii (14.5%), shown in
Table IX. Fifty-five burrows were on the flatter area of
the plot, where Ambrosia dumosa was the most dense species.
The affinity for constructing burrows under Larrea tr iden-
tata is probably a reflection of its relative density as
well as (especially with regard to A. dumosa) its larger
volume, which provides more protective cover.
Plant size may have been the reason for the preference of
Yucca schidigera over smaller shrubs of comparable or greater
density (App. XIII). The remainder of the shrub choices does
not indicate a preference.
Northerly-, southerly- and westerly-facing apertures (es-
pecially the latter) were most preferred; southeaster ly-fac-
(
(
I
41
")
)
Table IX. The perennial vegetation over 62 burrows, compared
to the relative density of each species.
Species
Number of
Burrows Found
Under Species
Larrefl tridentata
Arnhrnm' n dumosa
** Yucca schidiqera
Krameria Gray ii
Eriogonum f asciculatum
Acacia Greqqii
Ephedra nevadensis
Stephanomeria pauci flora
*Bacchar is brachyphy 11a
Opuntia ramosissima
*0_. acanthocarpa
Krameria parvif olia
*Encelia sp.
Salazar ia mexicana
*Erioqonum inf latum
Dyssodia porophylloide;
Lycium Andersonii
35
18
11
9
4
3
2
1
1
1
1
1
1
1
1
1
1
56. 5
29. 0
17. 7
14. 5
6.5
4. 8
3.2
1.6
1.6
1.6
1.6
1. 6
1. 6
1. 6
1.6
1.6
1.6
Relative Density
Flats
9.0
19. 2
0. 5
2. 7
0. 5
1.1
Rolling
Hills
■ 10. 6
15.9
0.2
4. 1
1. 3
0.2
2.7
1.3
5.6
0.4
* = occurred in rolling hills
** = three burrows were in rolling hills
ing openings were least preferred (Figure 10). Auffenburg
and Weaver (1969) found that southerly-facing apertures were
most common for Arizonian tortoises; Karl (1979a) similarly
f
(
(
42
reported that southerly to westerly directions were most
preferred in the western Mojave Desert. The sample
size for each direction was too small .( = 0-8) to determine
if there was a directional change from month to month,
although the advantages of earliest solar irradiation would
be derived by tortoises in easterly-facing burrows, thus
provided a longer activity period over tortoises se-
questered in burrows of other aperture directions.
)
TV
Figure 10. Aperture directions of
104 burrows.
Of 106 burrows, only 9 were not straight. Five curved
to the right and four curved to the left. Burge (1978) also
noticed turns in a few burrows.
(
(
«
43
1
The width of the burrow indicates the approximate size of
the tortoise inhabiting it (Karl, 1979a, b). Of 108 burrows,
the average of the burrow width at the entrance compared
to the carapace length of the associated tortoise was 119.5%
(range: 59-288%). One tortoise had to tilt to enter her bur-
row.
Few tortoises were found in the same burrow on successive
captures. Burrows which were associated with specific tor-
toises were often found unused at a later date. Additionally,
several times I found several burrows in a small area (e.g.
5 in a 200 X 300 m section), but no tortoises. These obser-
vations indicate that tortoises occupy several burrows apiece.
In fact, 18 tortoises were observed to change burrows once,
5 changed twice and 1 changed 3 times. Up to three burrow
changes per tortoise were also observed by Karl (1979a).
Burge (1978) observed several changes in primary coversites;
however, most of these were non-burrow coversites. She also
noticed inter-year fidelity to specific burrows.
Hatchling Behavior. One hatchling was observed without
disturbance for 1.5 hours on 5 May. He was initially observ-
ed exiting from a shallow cavity in the ground at 0839 h and
T of 31.2°C. He walked 3 m across open ground to a large
gs
boulder, where he remained motionless, in the shade, until
0951 h, with the exception of the period from 0916 to 0926 h,
when he moved into the sun and remained motionless until he re-
turned to the boulder. At 0951 h, he walked 3 m, grazing,
to a rodent hole in a shrub, which he entered at 1003 h
<
<
t
AA
after scratching twice with a forefoot. He remained close
to shrubs two-thirds of the time during this journey, but
the close spacing of the shrubs made it impossible to de-
termine if this was coincidental. As heating and cooling
rates are relatively fast in very young tortoises ( Voight,
1975) it is likely that this hatchling maintained an op-
timum metabolic rate by his brief movements into the sun.
Travelling in the open for such short periods is also a
reason for the increased difficulty in sighting this size
tortoise .
Movement . The greatest straight line distance between
capture points (SLD) was moved by an adult male, 1000 m in 18
days. For tortoises captured more than one time for which
the cumulative SLD's were much larger than the distance be-
tween the original capture and final recapture points, 8 males
averaged cumulative SLD's of 745 m (standard deviation = 490)
and 3 females averaged cumulative SLD's of 500 m (standard
deviation = 22). Heatwole (1976) and Burge (1977b) reported
that males have larger home ranges than females. An error
associated with correlating SLD to sex or size when captures
and recaptures are several days apart (the average interval
during this study was 26 days) is that large, undetected
-movements can occur between captures. For example, 1 adult
female moved 300 m in 1 day and 1 adult male moved 400 xn in
1 day. However, it seems reasonable that if SLD's are sim-
ilar regardless of the time interval between captures,
then an approximation of the average distances
f
c
«
45
-)
travelled by tortoises can be obtained. The mean SLD for
addlts (the only size class for which the sample size was
moderately large) was <275 m (Table X). However, wide vari-
ation occurred, resulting in large standard deviations. This
precluded forming conclusions about movement relative to
size or sex. Swingland et al (1978) reported that movement
was directly proportional to size in Geochelone gigantea .
Table X. Average straight line distance moved between cap-
ture points. Range is in brackets [ ] ; standard deviation
is in parenthesis ( ) .
Size
Class
Se
f
x
0*
All
Individuals
Adult
188 (85)
[ 0-375]
n=22
271 (194)
[ 0-1000]
n = 38
244 (168)
[ 0-1000]
n=61
Subadult
100 (77)
[ 0-225]
n=10
408 (310)
[75-750]
n = 6
216 (244)
[ 0-750]
n=16
Immature
75 (35)
[50-100]
n=2
625
n=l
190 (187)
[50-625]
n=8
Juvenile II
25 (35)
[ 0-50 ]
n=2
Juvenile I
100
n=l
Feeding Behavior . Lotus sp p, especially Lotus tomentell-
u_s, were apparently preferred as they were eaten in 63% of 46 ob-
served feedings by 21 tortoises. In addition, in one instance,
f
(
c
46
1
a tortoise walked over Schismus sp . (which he sniffed) , Plan-
tago insular is , Cryptantha spp . , Eriogonum spp. and Euphorbia
polycarpa and only ate one of the scarce Lotus sp . plants in
the area. In another instance, a tortoise ate three of the
four nearby Lotus sp . plants available to the exclusion of
other plant species. Between 7 and 14 June, 36 moderately
fresh scat and 1 fresh scat were examined for content; 34
(89.2%) contained Lotus sp. pods, 2 (5.4%) contained Opuntia
basilar is glochids and 1 (2.7%) had a grass floret. Karl
(1979b) also observed a preference for legumes, especially
Lotus salsuginosus . This preference may be due to the suc-
culent nature of Lotus spp. None of the other observed
forage species, save for the Opuntia basilar is , were succu-
lent.
Lotus spp. (primarily L. tomentellus ) had the fourth
greatest average importance value for the entire plot. It
was also the most frequently encountered species in the
rolling hills in early May and only slightly less frequent-
ly encountered than Pectocarya spp. and Plantago insularis
here in early April. Also, its relative cover was only slight-
ly less than Chorizanthe brevicornu (which had the highest
relative cover) in early May in the hills. However, it other-
wise had consistently less cover than Pectocarya spp. and
Cryptantha spp., and, in early May on the flats, Eriogonum
spp. (Appendix XIII). It was also far less frequently encount-
ered on the flats than these three genera. So, although
borages and sometimes Eriogonum spp. were primarily predomi-
t
c
c
nant with regard to cover and were most frequently encounter-
ed on the flats (ca two-thirds of the plot) , they were far
less preferred than Lotus spp.
47
Table XI. Forage species of 21 tortoises. In all cases, the
plants were green.
Speci.es
Lotus tomentellus
Lotus sp .
Possible Lotus sp.
Cryptan tha augus ti f ol ia
Astragalus sp .
Pectocarya sp.
Possible Pectocarya sp.
Amsinckia tessellata
Cryptantha gracilis
Possible borage
Opuntia basilar is
Stephanomeria exiqua
Number of
Plants Eaten
12
16
1
6
2
2
2
1
1
1
1
1
Plant Part Cons urn ea; # in
( ) Is # of Times Eaten
Aerial parts (9)
Leaves (2); aerial parts (14)
Undetermined
Aerial parts (6)
Aerial parts (2)
All aerial parts, including
green fruit (2)
Undetermined
Flower
Undetermined
Undetermined
1/2 of a 12 X 10 cm pad and
possibly the fruit
Leaves
Except for three instances, all observations of feed-
ing on plants occurred between 5 April and 8 May when most
annuals were flowering (Pectocarya sp. was primarily dried
by 8 May). The remaining three sightings were on 8 and 15
June and were of Cryptantha augustifolia and a possible bor-
f
(
c
4R
age. At this time, C. augus t i folia , a few remaining Lotus sp. ,
Chaenactis carphocl i na and Er iogonum de f lexum were the only
green annual species. Thus, it would appear that there is a
tendency to feed on green plants, rather than dried ones.
When Lotus sp. is unavailable, tortoises probably feed on
most other available species. Swingland and Coe (1978) de-
scribed Geochelone g inantea as a "broad-spectrum, opportunistic
herbivore... (consuming) virtually all litter".
All available forage was not eaten. Two tortoises
walked over Plantago insularis, Pectocarya s p p . , Cryptan-
tha s p p . , Chor izan the r ig ida , Euphorbia polyca rpa , S tephan-
omeria exigua , Chaenac t i s spp. and Astraga lus acutirostris
(which was smelled by one tortoise) , as well as Lotus sp.. ,
and ate nothing. These sightings occurred on 27 April
and 3 May, when all of these plants were green. In another
observation, a tortoise walked within 4 cm of 2 small Lotus
sp. plants and over another, but ate 2 other Lotus sp. plants.
In nine instances, tortoises ate only a portion of several
Lotus sp. plants, dropping detached portions on the ground
in two instances. Only one plant was entirely devoured. It
is possible that Lotus sp. plants which were not eaten were
simply not noticed. Tortoises seem to use vision as a pri-
mary sensory mode, looking more or less straight ahead with
some head turning. It was also suggested by Manton (1979)
that vision is the primary stimulus for food location. Dur-
f
c
c
49
ing late spring when many of the annuals were dried, a tor-
toise was observed repeatedly sniffing at, but not eating,
several Euphorbia polycarpa plants, the sole green, prostrate
plant species in an area which lacked Lotus sp . Perhaps
the tortoise was visually stimulated by the similarity of
.the species habit to that of Lotus sp., but found it to be
E. polycarpa instead by olfaction {if the "sniffing" is
olfactory) .
Borages, consumed in 26.1 to 28.3 per cent of the ob-
served feedings, were not always chosen as forage when recog-
nized. In one instance, a tortoise at from four Cryptan tha
augusti folia plants (devouring all of two) , but avoided two
others after "sniffing" each.
Three tortoises, a Subadult and two juvenile II's, were
observed eating dirt. The former ate dirt from shallow,
scraped areas, ca 10 cm in diameter, several of which were
present in a 10 m circle. He ate many bites of the packed
dirt, remaining at a "feeding" site up to 3.5 minutes at a
time. He may have ingested a rabbit pellet as a few of these
were present in one depression. Occasionally he scraped
the dirt with a forefoot. Tortoise tracks could not be dis-
cerned in the bare dirt patches, although there were punctures
and some single, linear scrapes. The second tortoise ate
dirt in a similar manner, possibly ingesting some of the u-
biquitous black lichen, and eating Lotus sp. in between eating
dirt. One of the dirt-feeding sites, 11 by 7 cm, had many
short, narrow, often parallel scrapes. The third tortoise
f
(
c
50
ate loosened dirt at one spot for six and one-half minutes.
Geophagy has been observed by Karl (1979a) and Sokal (1971).
One tortoise ate part of a kit fox scat which was com-
pletely composed of hair.
Courtship and Coition. Copulation was observed on three
occasions, 6, 14 and 25 April. Males were 257.5 to 269.5 mm
MCL and all were young adults, judging from their shell wear
(rings distinct or nearly so, hatchling plate present on
posterior costals of one tortoise). Females were 222.5 to
237 mm MCL an d all appeared to be past their "prime" (with
sinking scutes and widening sutures); one tortoise was old
(scutes sunk, sutures wide, smooth marginals' edges). All
pairs were already copulating when found. In one couple,
the male remained mounted for seven minutes. (Karl, 1979a,
previously described the position and movements of mounted
males, identical to this male's.) During this time, the female
remained still, initially, only a few seconds at a time and
pivoted often. Just prior to the male's dismount, she was
pivoting constantly. The male from the second pair dismount-
ed almost immediately after being sighted. Both dismounted
males lay next to the females and head-bobbed for a few se-
conds. Both females walked away from the males only a few
seconds after the males dismounted and began to graze. One
male remained in place two minutes prior to turning away from
the female and walked a few meters away. The second male
head-bobbed until the female was eight meters away, at which
f
(
c
51
point he stopped bobbing, turned and walked away.
One mating area was dry with a few concentric 1/4 circles
and several tiny depressions. The mating area of another pair
was moist but had no well defined rings or depressions from
the male's pygal or feet. The third pair both had moist anal
areas .
On 28 March, 2 tortoises were in the same burrow, the
218 mm (in middle adult years, judging by shell wear) female
sideways and in front of the 257.5 mm male (one of the males
found copulating, above) . On 25 March, a 259 mm male ( in mid-
dle adult years) was following a few centimeters behind a
212 mm female (young adult) .
Activity During Handling, There was a much higher per-
centage of active tortoises under 180 mm MCL, 49.2% (n=59) ,
than over 180 mm MCL, 12.6% (n=142). The highest proportion
of very active individuals for an age class occurred in
tortoises under 60 mm MCL. One hatchling attempted to bite.
Generally, individual behavior did not change during succes-
sive recaptures.
Tortoises voided amber, orange, pink or clear urine.
Precipitates were light brown, lavendar, pink or white, the
white precipitates often creamy and the colored curdled.
Sometimes precipitates were mucilagenous and the consistency
of cooked, shredded albumin. Precipitates were present in
56.9% of 137 voids. There was an increase in the presence
of insolubilities in the voids during June and March (.50.^0%
each month) over April (38.5%) and May (38.2%). Of 12 times
c
t
t
52
when the urine was relatively viscous, 6 occurred in June.
The June increases in precipitates and viscosity may be in-
dicative of decreased water intake because of decreased green
forage in June. Light feeding (due to general inactivity) in
March may be responsible for the lack of insolubilities in
the urine then. Nagy and Medica (1977) noted that osmotic
concentrations in bladder urine increased from May to June.
High osmotic concentrations result in large quantities of
gelatinous urate precipitates and dark brown urine (Minnich,
1977) . Females, only, voided on fewer occasions with approach-
ing summer (Table XII). Also, the only large change in void-
ing behavior of individual tortoises occurred in June in a-
dult females; 14 tortoises which had voided on a capture prior
to June did not void on recapture in June (although 2 females
changed to voiding behavior in June). Nagy et al (1977) ob-
served that breeding females retain water. This would be es-
pecially important as osmotic concentrations increased with
drying forage.
Table XII. Per cent of captures each month which voided,
relative to sex.
Month
f
¥
Undetermined
March
20.0
(n=10)
8 5.7
(n=7J
100
(n=5)
April
48 .8
(n=41)
63.6
(n=22)
95
(n=20)
May
68.2
(n=22)
76.2
(n=21)
85.2
(n=27)
June
57.9
(n=19)
46.2
(n=13)
91.7
(n«12)
f
•
I
53
Smaller tortoises voided more often during handling than
larger ones (Table XIII) . Adult females voided more consis-
tently than adult males.
Table XIII. The percentage of tortoises of each sex and
size which voided during handling.
\s ize
Vlass
Sex\
Adult
Subadu It
•
Immature
Juv . I
Juv. II
Hat chling
J1
45
(n=80)
76. 9
(n=13)
100
(n=2)
?
64 . 3
(n=42)
76. 5
(n=17)
50
(n = 4)
Und.
88. 5
(n=26)
89. 7
(n=29)
100
(n = 7)
100
(n=2)
The greatest volume voided during a capture (expressed
as the percentage of body weight) was by tortoises under
100 mm MCL (Table XIV). There was little difference between
immature tortoises of undetermined sex (for those of deter-
mined sex, the sample size was too small to formulate com-
parisons) and subadult and adult females. However, subadult
and adult males voided less than females.
Six scats were excreted by five tortoises. They ranged
from 12.1 to 27.8% of the carapace length. Four of the scats
were examined for content. All had fine (*0.5 mm in diameter)
and/or medium-sized ( ca 1 mm in diameter) stems; pods were
present in 3 and a rodent scat was in 1 other.
An adult female tortoise excreted a stone, ca 15 mm in
diameter, and weighing slightly less than 2 g (dry weight).
f
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54.
Table XIV. Average volume voided for each age class
and sample size are in parentheses ( ).
Range
Size
Class
Sex
Adult
Subadult
Immature
Juvenile II
Juvenile I-
Hatchling
S
0. 75
(0. 02-2 . 7)
(n=37)
1 .22
0. 52
(0.1-2. 1)
(n=ll)
1.04
4.1
(n-1)
0.8
¥
(negligible
to 5.5)
(n=26)
(neg. -3.8)
(n=12)
(0.2-1.4)
(n=2)
Und.
1.27
(0.3-4. 1)
(n=23)
(0.6-13. 9)
(n=24)
(2 . 9-15. 2)
(n = 6)
Other Data
Vegetation . It was occularly apparent that the annual
vegetation was not yet at its peak on 25 March; little was in
bloom. However, most annuals peaked in April. Large de-
creases in biomass and cover and small decreases in frequen-
cy were evident between 5 April and 5 May (Table XV) . For
those species whose combined, relative importance value for
both months was >10, only Chor izanthe brevicornu , in *the
rolling hills, and Er iogonum spp . , on the flats, increased
in frequency, biomass and cover from April to May. Although
the cover of Chaenactis spp. increased from April to May on
the flats, the biomass and frequency changed little. Chor i-
zanthe brevicornu , Er iogonum maculatum, Cryptantha augusti-
f o lia and Plantago insularis along with several minor (in
importance value) species (Eriogonum def lexum , Chorizanthe
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56.
rigida , Nemac ladus rubescens ) were in full flower and foliage
in early May. By this time, Pectocarya spp . had dried. The
only green annuals in late May and early June were occasional
Lotus spp. and Cryptantha spp. (both of which were drying)
Chaenactis carphoc lina , Eriogonum def lexum and E_. maculatum .
Lotus spp. did not decrease in cover or frequency between
the April and May samplings, but plants were beginnning to
dry in May, as reflected by decreased biomass. On the flats,
cover increased slightly (Appendix XIII), probably due to
the small sampling length (50 m) covered in each sampling
period and the possible resultant small pockets of homogen-
eity. One fault with this sampling technique is that it
extends over a very short length and even if it is transected
through a homogeneous community, some heterogeneity occurs
in the transect which influences the resultant importance
of each species. If the transect were longer, either with
more sampling plots or by skipping every other 2X2 m plot
(maintaining the same number of sampling points but extending
the transect line), then the expression of homogeneity for"""
the transect would be greater.
Pectocarya spp. and Cryptantha spp. are important annuals
on the entire plot (Table XV) . Diversity is evident between
the rolling hills and the flats as Lotus spp. and Plantago
insularis are especially important in the former and Eriogo-
num spp. and Chaenactis spp. are more important on the flats.
Although biomass and frequency vary little between the two
areas, with the exception that biomass in the rolling hills
r
c
♦
5?,
was much less than that on the flats in early May, cover is
much greater on the flats.
Euphorbia poly carpa is the dominant perennial over
the entire plot (Table XVI). However, in the shrub layer,
Larrea triden tata and Ambrosia dumosa are dominant on the
flats and Er iogonum f asc iculatum and Ambrosi a dumosa are
dominant in the rolling hills. Only 9 species were pre-
sent in the transect on the flats; however, 23 were tran-
sected in the rolling hills. Not only is diversity great-
ly increased in the latter area, but density and frequency
are- high relative to the flats. However, the volume of the
shrubs on the flats is much greater, reflected by a far
taller and thicker shrub layer there.
Most perennials bloomed between mid-April and early
May, with the exception of Acacia Greggii , which was just
beginning to leaf then, and Kramer ia spp. and Ferocactus
acanthodes, all of which bloomed in early June.
Table XVI
Major perennial sp
ecies in each transect.
Species
Density
(#/ha)
Volume
X . 108
(cm3/ha)
Frequency
Importance
Value
Transect
II
Euphorbia polycarpa
Larrea tridentata
Ambrosia dumosa
All species
6150
850
1800
9400
0.0009
10.43
2. 755
22.1
0.38 .
0.3
0.46
1. 38
31.0
26. 3
21.7
100. 0
Transect
I
E. polycarp;
Eriogonum f asciculatun
12150
4450
2950
28100
0.0193
1.9095
1.1024
8.433
0.64
0.60
0.64
3. 84
20.0
18.0
13.4
100.0
A. dumosa
All species
f
f
4
SUMMARY
58
One hundred and forty-two tortoises were captured. Den-
sity is estimated at 63 tortoises/km^ (= 160 tortoises/mi ) .
It is suggested that censusing be more frequently performed
on small, random areas of the plot rather than the entire
plot for determining density by the Schnabel technique.
Fewer tortoises were found in the rolling hills and
2
rock outcrops and an estimate of 31 tortoises/km (= 80 tor-
2 2
toises/mi ) for these areas and 77 tortoises/km ( = 200 tor-
2
toises/mi ) for the flats is made. Reasons for the lack of
tortoises in the rock outcrops include decreased burrowing
and nesting potential, thermoregulatory disadvantages, de-
creased food availability and increased energy expenditures.
The size structure yields 45.8% Adults, 12.0% Subadults,
17.6% Immatures, 19.0% Juvenile II's, 2.8% Juvenile I's and
2.8% Hatchlings. Reproduction is high, reflected by a high
percentage of tortoises under 135 mm MCL, indicating that
carrying capacity has yet to be reached. The percentage of
adults is not low and only 21.4% of the females and 10.9% of
the males are old and possibly senile. The sex ratio of
adults yields only 0.55 females : 1.0 male to 0.61 females :
1.0 male. High winter rainfall (which would be responsible
for high spring primary production) 7, 2 and 1 years ago and
high summer rainfall (which would provide high production of
winter annuals and allow for heavy fat deposition prior to
59
hibernation) 2.5 and 4.5 years ago may have been influential
in the population increase. There was, however, high repro-
duction 7 to 10 years ago, when rainfall was low. It is pos-
sible that this descrepancy is attributable to the difficulty
of assigning carapace length to a specific age.
Seventeen skeletal remains, representing one tortoise
each, plus thirty-one small groups of isolated fragments
were found. Highest recovery was in adults, 52.9%. Mortal-
ity is estimated at 3,4 tortoises/year (=2 . 1%/year ) . Small'
sample sizes precluded forming conclusions regarding differen-
tial sexual mortality.
Females were observed to have a prominant pygal tip,
while that of males was pointed straight down or tucked under.
Greatest growth was by a 53.5mm MCL tortoise, 0.38%/day
in length and 1.84%/day in weight. The growth rate in length
was 0.033%/day greater for adult males than for adult females.
However, there was no sexual difference in weight gain, pos-
sibly because the weight gain accompanying length gain in males
equalled the weight gain accompanying developing follicles in
females. This hypothesis may be borne out by the observation
that there was no length growth rate difference between sub-
adult males and females but subadult females gained 0.13%/day
more in weight than subadult males. No intaseason variation
in growth rate was observed. New growth was first observed
in April but slacked off in June.
For young tortoises, it was determined that one ring ap-
proximately equals one year of age.
60
Tortoise activity coincided with ground temperatures of
ca 20 to 43°C, although tortoises were observed in retreat at
temperatures ^35°C and <29°C. Tortoises began activity at
ca 1030 h in March, becoming active increasingly earlier with
warming weather, as early as 0545 in June. Midday retreats
occurred in April (1100 to 1500 h) , May (1200 to 1500 h) and
June (1000 to 1600 h). Activity ceased by 1500 h in March,
1700 h in April, 1730 h in May and 1800 h in June. Tortoises
were equally active in the morning as in the late afternoon.
Activity was greatest in April and May.
Burrows seemed to have been preferred retreat sites dur-
ing midday as the season progressed and during the evening.
However, 81% of 16 epigean retreats (the time of day of us"e
was not determined) were found in April and May. Burrow lengths
remained relatively constant thoughout the season, 0.38 to
0.64 m.
Most burrows were constructed under shrubs, probably due
to the visual obscurity provided there as well as the possi-
bility of looser soil. The predominant cover species was
Larrea tridentata (over 56.5% of 62 burrows) , probably due to
its large volume, as its relative density was less than that
for Ambrosia dumosa , which was the second greatest cover
species (over 29% of the burrows). Burrow location did not
change from month to month. Northerly-, southerly- and west-
erly-facing apertures were most common.
Tortoises occupied several burrows apiece; up to three
burrow changes per tortoise were observed.
c
61
One hatchling was observed for 1.5 hours. It remained
primarily in the shade, possibly for maintenance of optimum
metabolic rate.
The greatest SLD was moved by an adult male, 1000 m in
18 days. The mean SLD for adults was 275 m, with wide varia-
tion .
Lotus spp. , primarily Lotus tomentellus , was the most
preferred forage species (possibly due to its succulence)
although it had only the fourth greatest importance value
for the entire plot. Green plants were preferred forage over
dried ones. Geophagy was observed in three tortoises.
Copulation was observed on 6, 14 and 25 April by males
257.5 to 269.5 mm MCL and females 222.5 to 235 mm MCL. All
males wer young adults and females were past their prime; one
female was old.
Small tortoises were more active during handling, voided
more often then and voided larger percentages of their body
weight than large tortoises . Females voided more often and
a larger percentage of their body weight than males. Urine
viscosity and precipitates increased during June,
Peak blooming and foliage occurred in mid-April. By early
May, most perennials were through blooming and many annuals were
drying. The biomass and cover of annuals decreased extensively
from early April to early May. Perennial's diversity is much
greater in the hills than on the flats. In the shrub layer,
Larrea tridentata is the most important species on the flats
r
(
c
62
t
and Eriogonum fasciculatum the most important species in the
rolling hills; Ambrosia dumosa is second to both in impor-
tance value. Pectocarya spp. and Cryptantha spp. have the
greatest importance value for the entire plot. However,
Lotus spp. and Plantago insular is are important in
the rolling hills and Eriogonum spp. and Chaenactis spp.
are important on the flats. A suggestion is made that
the transect be lengthened to accomodate pockets of hetero-
geneity .
>
ACKNOWLEDGEMENTS
I am extremely grateful to Paul Melograno and Peter
Woodman for their fine field work. I am indebted to
Bill Mautner for reviewing portions of this transcript
and to Janet Mautner for the use of her typewriter-f or-
people-who-continual ly-make-mistakkes (sic) .
>
(
(
63
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ku^
>
>
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Sceloporus virgatus . Ecology, 56:172-182.
Voight, W. 1975. Heating and cooling rates and their effects
upon heart rate and subcutaneous temperatures in the de^
sert tortoise, Gopherus agassizi . Comp . Biochem. Phys.,
52A:527-531.
c
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69
Woodbury, A. and R. Hardy. .1948. Studies of the desert tor-
toise, Gopherus agassizi . Ecol. Monogr., 18:145-200.
Yntema, C. 1976. Effects of incubation temperatures on sex-
ual differentiation in the turtle Chelydra serpentina.
J. Morph. , 150:453-458.
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 .
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70
Appendices I-V.
I. Locations of live tortoises.
II. Locations of skeletal remains.
III. Locations of predator sign.
IV. Vegetation.
V. Geomorphology .
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arm*»nri 1 v V
Appendix I,
tortoises .
Locations of live
N
71
75.
1» 100 m
mr interval is 20*
3i,f
jf
>t boundaries are heavy ryes.
»
1 * ' >i' <v -=l - • -Writ ._5H» .• -J i* . .. -^ ^ "'' > »f -• A/7 *//» - >/ -
b^o.20' ^ ^aft^.-tf %a.
-<?^
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,</<)
si
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S27
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Appendix II. Locations of
skeletal remains.
N
72
75.
j» 100 m
u Mr interval is 20' . ^
ot boundaries are h< ^ *y lines
S28
»
S27
>
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1 — ..^..waa v. beomorDholoqy.
Appendix III. Locations of predator sign.
\^J = Coyote burrow X = Predator sighted
= Kit fox burrow
= Burrowing Owl burrow
= Fresh burrow
•••• = Predator e
xcavations
N 7
* 75.
I
S27
>
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I
ppendix IV. Vegetation.
Larrea-Ambrosia-Yucca schidigera
• %
community
V«**- Very diverse upper story (Erio-
gonum f ascicula turn and Ambrosia
o
'
1 slightly dominant)
w«umjai.j.co a JL t; UKdVy Hill
bZti
= Fouguieria , Salazaria, Acacia
Lycium, Cassia
= Predominantly Encelia f ar inosa
= Physalis , Bacchar is , Nicot iana
Ho fmeisteria , Hap lopappus Good -
dingii
74
75.
S27
•.V
•■*-V>.*Vi • • •• • A» p. ••
►IT
.«• • •
f > » la i n> -r? i .-»r s % — * 1 '"- Tu*. » v
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Appendix V. Geomorphology .
— —«■»••''•— e Watercourse
•••..'.•'^/..'•i: = Major Wash
j -|" 100 m
:o ur interval is 20' m
>lot boundaries are heavy lines,
f
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>
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76.
Appendix VI. Standard form for
recording live tortoise data.
)
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Appendix VI. Standard form for recording live tortoise data
77
>
Site (UsadJL
Gopherus agassizi
(
Co. S^,m .Bc/nC .
£iev. g , ?,fr f
No._
Sex
Date
^ZjS.
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Time(PST) ggj
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wind/cloud cover /j /<*, e#2& L Y. %S£&
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Note site of epoxied
number. /J0
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Appendix VI, continued.
78
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79,
Appendix VII. Desert Tortoise
Shell Data Card.
>
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Appendix VI I .
tsu .
DESERT TORTOISE SHELL DATA CARD
DATE OF CARD
RECORDER
J-/6*S
CARD NUME
DATE FO^ND^ f^-
f -2 ?-f O
COLLECTOR f-sO/cfXjL&&£
ILL NUMBER
3 /
SEX
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MUSEUM
MUSEUM NUMBER
ELEVATION
GEOMORPHOLOGY
/3*~/***Ca
SOIL TEXTURE-PARENT MAT'L
OTHER HABITAT USES
VEGETATION
*£&
TOPOGRAPHIC QUAD
NAME
<^£jA£&&i /3*/r
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SUBDIVISION
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SITE NAME
CONDITION OF SKELETON
ENTIRE
LEG BONES
A>*
COLOR OF BONE tf0T&y
6 Act- stt*»'<*"S-
AGE OP BONE: SOLID
PEELING & CHIPPING
CRUMBLING
/
BROKEN
Pi.
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/
VISCERA
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TpvTZ
CONDITION OF SCUTES
NONE
POSSIBLE MORTALITY FACTORS*""1* '
NORMAL COLOR
UNKNOWN.NO MARKS
ADHERED TIGHTLY TO BONE
PREDATOR.CHEW MARKS
PLASTKON/tAAAPACC- SCUTES Of P
•
BULLET HOLES
SCUTES LOOSE & PEELING
VEHICLE
SCUTE FADED. GROWTH RINGS PEELING
•
OTHER
TORTOISE REMAINS IN PREDATOR SCAT
LIMB OR HEAD PRESENT ONLY
MEASUREMENTS *
UNITS
H
P: PLASTRON H '• ViHgWt L: LENGTH
SCUTES
..
MAX. P.L.
MIN.P.L.
C.L.
/? ?*1 V^tS'
3-4 mw 6s*«*»
7- i MW«> 4t»'
C: CARAPACE
M MARGINAL
W. WIDTH
KEY
Y^/j ■ pitt*» prtstnt( intact
,/ pitctr frit****, n»iw«T»d
fr»y.e*t* (*<■*• location)
fl : hot present
DOr^eS
I** ir.d.c«rt hti)ji<r(mti1 e"^ bo<.«bo>\t o<- 5cqte--bon«. u>itk »• • gjT«twt< a<t clary if no n«aJur(<>it«1r a^( 4ut
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81.
Appendix VIII. Desert Tortoise Council
notching system.
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Appendix X. Skeletal
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107
Appendix XII. Vegetation of
the study site.
108
Appendix XII. Vegetation of the study site; (a)=annual and
(p) =perennial .
Asclepiadaceae Cactaceae, continued.
Asclepias subulata (p) 0. Bigelovii (p)
)
Funastrum he terophy Hum (p)
Boraginaceae
Amsinckia tessellata (a)
Cryptantha augustif olia (a)
C. c ir cumcissa (a)
C. decipiens (a)
C_. gracilis (a)
C. holoptera (a)
C. nevadensis (a)
C. pterocarya (a)
C. racemosa (p)
C. utahensis (a)
Pectocarya penicil lata (a)
P. platycarpa (a)
P. recurvata (a)
Cactaceae
Echinocereus Engelmannii (p)
Fero cactus a canthodes (p )
Mammillaria microcarpa (p)
Opuntia acanthocarpa (p)
0. basilaris (p)
0. echinocarpa (p)
0. ramosissima (p)
Compos i tae
Acamptopappus sphaeroce-
phalus (p)
Ambrosia dumosa (p )
Bacchar is brachyphylla (p)
Baileya pleniradiata (a)
Chaenactis carphoclina (a )
C. Fremontii (a)
C. stevioides (a)
Dyssodia Cooper i (p)
D. porophyloides (p)
Encelia f ar inosa (p)
E. virginensis (p)
Eriophy Hum Wallacei (a)
Haplopappus Gooddingii (p)
Hofmeisteria pluriseta (p)
Hymenoclea Salsola (p)
Machaerantha tortoif o-
lia (p)
Malacothrix glabrata (a)
109
1
Monoptilon bel lioides (a)
Pectis papposa (a)
Per ity le Emory i (a )
Peucephyllum Schottii (p)
Porophy Hum gracile (p)
Psathyrotes sp . (a)
Psilotrophe Cooperi (p)
Stephanomeria exigua (a)
S . Parryi (p)
S. paucif lora (a)
Tr ichoptilium incisum (a)
Trixis calif ornica (p)
Cuscutaceae
Cuscuta sp
)
Crucif erae
Caulanthus Cooperi (a)
Descurania pinnata (a)
Draba cuneif olia var . in-
teqrif olia (a)
Lepidium Fremontii (p)
L . lasciocarpum ( a )
Lesquerella Palmer i (a)
Streptanthella longiros*-
tris (a)
Cucurbitaceae
Cucurbita palmata
Ephedraceae
Ephedra nevadens is (p )
Euphorbiaceae
Euphorbia polycarpa (p)
Stillingia paucidenta-
ta (p)
Fouquieriaceae
Fouquieria splendens (p)
Geraniaceae
Erodium cicutarium (a )
Graminae
Aristida sp. (p)
Bromus rubens (a )
Er ioneuron pulchellum (p)
Schismus sp. (a)
Stipa speciosa ( p )
Hydrophyllaceae
Eucrypta micrantha (a)
Nama demissum (a)
<
110
1
Hydrophyllaceae , continued.
Phacelia crenulata (a )
P. tanacetif olia (a)
Labiatae
Salazaria mexicana (p)
Salvia columbariae (a)
Leguminosae
Acacia Greggii (p)
Astragalus acutirostris (a)
Cassia armata (p)
Dalea Fremontii (p)
D. mollis (p)
Krameria Grayii (p)
K. parvif olia (p)
Lotus salsuginosus brevi-
vexillus (a )
L. tomentellus (a)
Lupinus concinnus var. Or-
cutti (a)
Liliaceae
Yucca schidigera (p)
Loasaceae
Mentzelia involucrata (a)
Lobeliaceae
Nemacladus rubescens (a )
Malvaceae
Sphaeralcea ambigua (p)
Nyctaginaceae
Mirabilis Bigelovii (p)
Oenograceae
Oenothera brevipes (a )
O. ref racta (a)
Papaveraceae
Eschscholtzia glypto-
sperma (a )
Plantaginaceae
Plantago insularis (a)
Polemoniaceae
Gilia interior (a )
Langloisia setosissi-
ma (a)
Linanthus aureus (a )
L. dichotomus (a)
(
<
Ill
1
Polygonaceae
Chorizanthe brevicornu (a)
C . rigida (a)
Eriogonum deflexum (a)
E. fasciculatum (p)
E. inflatum (p)
E. maculatum (a)
E. nidularium (a)
E. tr ichopes (a)
Resedaceae
Oligomer is linif olia (a)
)
Rubiaceae
Gallium stellatum (p)
Scrophulariaceae
Mimulus Bigelovii (a)
Solanaceae
Lycium Ander sonii (p)
Nicotiana trigonophylla (p)
Physalis crassifolia (p)
Zygophyllaceae
Larrea tridentata (p)
(
(
(
1
Appendix XIII. Vegetation analysis
112
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Appendix XIII, continued. 117
B. Perennial vegetation, listed in decreasing order of importance value.
Species
Dens
Abs .
(#/ha)
;ity
Rel .
%
Tran
Volume
PihS.
(cm3/ha)
sect I
Rel .
%
Frequency
Abs'. Rel.
I .V.
Euphorbia polvcarpa
12150
43.2
0. 0193
xio8
0.21
0. 64
16. 7
20. 0
Erioqonum fasciculatum
4450
15. 8
1.9095
xio8
22 . 64
0. 60
15. 6
18. 9
Ambrosia dumosa
2950
10. 5
1. 1024
xio8
13 . 07
0. 64
16. 7
13.4
St ephanomeria pauci-
f lora
1150
4.0
0. 8789
xio8
10. 42
0. 36
9. 4
7. 9
Porophyllum qracile
1850
6. 5
0. 2343
xio8
2. 78
0. 30
7. 8
5.7
Krameria parvifolia
750
2. 7
0. 5922
xio
7. 02
0. 24
6. 3
5. 3
Erioqonum inflatum
1550
350
5.5
1.2
0.0717
0. 6696
xio8
xio8
0. 85
7. 94
0. 22
0. 10
5. 7
2 . 6
4. 1
3. 9
Encelia virqinensis
Baccharis brachyphylla
350
1.2
0. 6163
xio8
7.31
0. 08
2. 1
3.5
Machaeranther a torti-
700
2. 5
0.0335
xio8
0. 40
0. 16
4.1
2. 3
f olia
Stephanomeria Parryi
800
300
2. 8
1. 1
0. 0075
0. 0176
xio8
xio8
0. 09
0. 21
0. 14
0. 10
3 . 6
2. 6
2. 2
1. 3
Gallium stellatum
Encelia farinosa
200
0. 7
0. 0005
xio8
0.01
0. 04
1. 0
0. 6
Dyssodia porophy loides
100
0.4
0. 0048
xio8
0. 06
0. 04
1.0
0. 5
Acacia Greggii
50
0.2
1. 7177
xio8
20. 37
0. 02
0. 5
7. 0
Cassia armata
50
0. 2
0.4248
xio8
5. 04
0.'0 2
0.5
1.9
Opuntia acanthocarpa
50
,0.2
0. 1168
xio8
1.39
0. 02
0.5
0. 7
Echinocereus Enqelmannij
50
50
0. 2
0.2
0. 0067
0.003 8
xio8
xio8
0.08
0.05
0.02
0. 02
0. 5
0. 5
0. 3
0. 3
Mirabilis Biqelovii
Acamptopappus sphaero-
50
0.2
0.0033
xio8
0. 04
0.02
0.5
0. 2
cephalus
Opuntia echinocarpa
50
0.2
0.0011
xio8
0. 01
0. 02
0. 5
0.1
Total
28100
100
8.4328
xio8
Tran
100
sect I
3. 84
I
100
100
Euphorbia polycarpa
6150
0. 65
0. 0009
xio8
0.004
0. 38
0. 28
31. 0
Larrea tridentata
850
0. 09
10.431
xio8
47. 2
0. 3
0.23
26. 3
Ambrosia dumosa
1800
0. 19
2.755
xio8
12.5
0.46
0.33
21. 7
Yucca schidigera
50
250
0.01
0. 03
7. 458
1.044
xio8
xio8
33.7
4. 7
0. 02
0. 10
0.01
0. 07
11.9
4.9
Krameria Grayii
Porophyllum gracile
100
0. 01
0. 1222
xio8
0.6
0. 04
0. 03
1. 5
Krameria parvifolia
100
0. 01
0. 1204
xio8
0. 5
0. 04
0. 03
1. 5
Ac am rtop ax>u s sph a e r acedia 1 u s
50
50
0. 01
0. 01
0. 1220
0. 0478
xio8
xio8
0. 6
0.2
0. 02
0. 02
0.01
0. 01
0.8
0. 7
Erioqonum fasciculatum
Total
9400
100
22 . 010
xio8
100
1. 38
100
100
c
(
C
Appendix XIV. Photographs.
Bureau of Land Management
Library V
Bldg. 5( i Federal Center
Denver, CO 80225
118
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