Front Cover
 Back Cover

Group Title: Bulletin of the Florida State Museum
Title: Gopherus berlandieri in southeastern Texas
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00001526/00001
 Material Information
Title: Gopherus berlandieri in southeastern Texas
Series Title: Bulletin of the Florida State Museum
Physical Description: 141-203 p. : illus. ; 23 cm.
Language: English
Creator: Auffenberg, Walter
Weaver, W. G. Jr. ( William Glenn ), 1936-
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 1969
Subject: Texas tortoise   ( lcsh )
Reptile populations -- Texas -- Cameron County   ( lcsh )
Reptiles -- Texas -- Cameron County   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Bibliography: p. 202-203.
General Note: Cover title.
Statement of Responsibility: by Walter Auffenberg and W. G. Weaver, Jr.
 Record Information
Bibliographic ID: UF00001526
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA0836
notis - ABS6298
alephbibnum - 000299846
oclc - 00822441
lccn - 74628699


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Table of Contents
    Front Cover
        Page 139
        Page 140
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    Back Cover
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Full Text





Volume 13

Number 3


Walter Auffenberg and W. G. Weaver, Jr.




lished at irregular intervals. Volumes contain about 300 pages and are not
necessarily completed in any one calendar year.

OLIVR L. AusTIN, JR., Editor

Consultants for this issue:

Communications concerning purchase or exchange of the publication and all
manuscripts should be addressed to the Managing Editor of the Bulletin, Florida
State Museum, Seagle Building, Gainesville, Florida 32601.

Price for this issue $.85

Pubbished May 15, 1969,


RI 141
Gq(a tz-
7- r 4.p


SYNOPSIS: Gopherus berlandieri populations on isolated clay dunes near the
mouth of the Rio Grande were studied intermittantly from 1961 to 1967.
Reproduction, growth, habitat, movement, activity, shelter, food, and predation
were investigated. The most important contribution of the study is the demon-
strated interpopulational behavioral variability in shelter construction and use,
activity range, and food preference. The geological and vegetational histories of
the habitats of each population are correlated with the behavioral differences


INTRODUCTION .......--------.......-----.---- ----. ------ ---------- 142
AREA CHARACTERISTICS ------...-......-------...... ... ----..---.-----.-143
Regional Features .--...--.....-------------.. .--.-..-.... --.------------143
Geomorphology and History ..............-----.......------------------------- 154
Nests and Eggs .--..----. -----..... ------- -------- ----------- 158
Hatchlings ................-------------------- ------------------------------166
Size --..._...........-------------------_...... .------------------ 168
.Growth 169
Growth ----------------------------------- ----------------------------- 169
Color ...............- ............- ......... .. .--------------- 171
Density and Distribution --.......-------...... ---....------------171
Movement -..--....- -........-----------------.. --------------------172
Activity Periods .........---.....----.-.... --.....---------------- 177
Orientation -.--.--.-.--.---------.- ---------------------------- 177
Shelter .. .............--------------------------- --- -- .--..----.--------180
Food and Feeding .--........------------.. ------. -------------------. 186
Color Preferences -...-........----------- ---- ----------------------- 188
Predation ----..-..--..-------.-.--------------- -------------189
DISCUSSION ---.....----...-.....-----..-..----. --------------------- 190
CONCLUSIONS --.--------....----.------------------........------.----- 199
LITERATURE CITED -.....----- -- ---..... -- ----------........ ----------- 202

1The Bulletin of the Florida State Museum has included several contributions
Son fossil tortoises by Walter Auffenberg, Curator in Herpetology, and on snake
anatomy by W. G. Weaver, former graduate student, University of Florida.
Manuscript received 3 August 1967.
Auffenberg, Walter and W. G. Weaver, Jr. 1969. Gopherus berlandieri in south-
eastern Texas. Bull. Florida State Mus., Vol. 13, No. 3, pp. 141-203.

6: :>'^





The present contribution represents a portion of the studies initi-
ated by Auffenberg on the systematics, comparative ecology, and
behavior of the genus Gopherus, of which the living populations
are believed to comprise two distinct species groups. Gopherus poly-
phemus, a member of one of these groups (G. polyphemus and G. fla-
vomarginatus), is currently being studied in Florida. Comparative data
for members of the other species group (G. agassizi and G. berlandieri)
are largely lacking. Preliminary investigations of the ecology and
habits of both G. agassizi and G. berlandieri were initiated to select
one of these species for more detailed studies. A survey of different
populations of G. agassizi within its range (W. A. field notes, 1962,
1963, 1964) showed so much variation in the ecology and habits of
this species that to pick a typical population for intensive study is
difficult. We know that Woodbury and Hardy's excellent study
(1948) represents a rather unusual situation, typical only of a re-
stricted area at the northern part of the species range, and including
only those populations living under rather specific conditions of soil
and climate. The frequency of such instances of behavioral adap-
tations by populations of all the species of Gopherus has stimulated
us to consider the vegetational, climatic, and geological facets of the
study area in more detail than is usual in such studies.
Preliminary studies throughout the range of G. berlandieri indi-
cated that this species is considerably less variable in both ecology
and habits than C. agassizi; thus we chose G. berlandieri for intensive
study. We found population densities near Brownsville, Texas higher
than in any other area investigated, and so selected this region as
the major study area. At this point the preliminary survey quickly
developed into a long term project with definitive goals. These were
to obtain appropriate data for comparing behavioral and ecological
aspects of the biology of G. berlandieri, as a representative of one
species group, with those of G. polyphemus as a representative of the
other group. Populations of G. agassizi and G. flavomarginatus are
to be studied similarly at a later date; some preliminary data have
already been accumulated on these two species.
The authors and their associates spent a total of 157 man days
in the field studying G. berlandieri after the project was initiated in
August 1961. Intensive study in the Brownsville area was begun in
May 1962 and continued in November 1963, July 1964, July and
August 1965, April 1966, June 1966, August 1966, and June 1967.


Vol. 13


Since 1961 one or the other of the authors has examined the habitat
of Gopherus berlandieri along almost the entire periphery of its range.
Field observations have been made from Aransas Pass westward
to San Antonio, southward to Eagle Pass and Laredo, and thence
to Monclova, Monterrey, Ciudad Victoria, and Tampico, Mexico;
W. G. Weaver did considerable additional work on behavior and
ecology at Sinton, Texas.
During the study several aspects of the biology of G. berlandieri
were investigated, but this report presents only those data bearing
on the movement, ecology, and certain morphological characteristics
of several essentially isolated populations near Brownsville. Where
pertinent, data from populations in other parts of the range are in-
cluded. Weaver plans to publish separately all data pertaining to
combat and courtship.

Without the aid of many individuals and institutions this study could not
have been completed. In particular we wish to acknowledge the receipt of
living specimens from several parts of the range from Bernardo Medina,
Brownsville, Texas; Michael Sabbath, University of Texas; and the late J. M.
Wilks, formerly of the Bob and Bessie Welder Wildlife Refuge, Sinton, Texas.
The University of Florida Herbarium was exceedingly helpful in the identifica-
tion of plant material. The American Philosophical Society provided the senior
author with a grant to initiate a study of Gopherus (Johnson Fund, 406).
Support during the subsequent period of research was provided by the National
Science Foundation (NSF GB1413 and 3738). Facilities and some financial
assistance were supplied continuously by the Florida State Museum. We also
wish to acknowledge the support offered the junior author by the Welder
Wildlife Foundation during the summer of 1965. The Graduate School, Uni-
versity of Florida, supported the important terminal trip to the study area in
August, 1966.
In particular we wish to thank Mr. A. B. Westbrook, City Manager, Browns-
ville, Texas for making his property available for our studies and for extending
every courtesy during our visits to southeastern Texas.

TOPOGRAPHY. The study area lies in the southeastern quadrant
of Cameron County, Texas, near the middle of the Tamaulipan Biotic
Province (Blair, 1950, 1952). Specifically it is in the area known as
Jackass Prairie a broad, treeless, saline plain dominated by coarse,
bunchy sacahuista (Spartina). This plain stretches 10 miles inland
north of the present natural levees of the Rio Grande. The most
studied tortoise population lives on the Loma Tio Alejos, a small,




isolated hill (loma) 400 feet north of the Boca Chica Highway
(Texas Highway 4) at its closest point; 14.5 miles east of the center
of Brownsville and 8.2 miles west of the Atlantic Coast of Boca
Chica Beach (Fig. 1). Completely surrounded by seasonally innun-
dated brackish water flats, the loma rises from 5 to 26 feet above
mean sea level at its highest point with a rather steep erosional scarp
from 10 to 20 feet above mean sea level around most of its periphery.
A gently inclined outwash plain lies between the base of the scarp
(10 ft. el.) and the outer edge of the loma (5 ft. el.). The loma top
is rather flat, sloping to the southeast from about 26 to 20 feet above
mean sea level. Its greatest length is 1800 feet and its shape from
above is roughly triangular (Fig. 2).
The loma is separated from other similar rises in the same plain
by intervening flats. The nearest surrounding rises are the Loma de
la Estrella, 2000 feet ESE; the Loma de la Jauja, approximately
3000 feet W; and two smaller lomas, Tia Tules and del Macho, 3500
feet N (Fig. 1). Gopherus berlandieri occurs on all these rises,
though population densities vary from one to the next. Because of
the ecology of the intervening flats, genetic interchange between
these populations is probably rare, if it occurs at all. Studies were
also conducted on a number of other lomas in the area, most of
them very similar to the Loma Tio Alejos except as noted below.
Som. The predominant soils of the deltaic plain near the mouth
of the Rio Grande are halomorphic, developed where evaporation
exceeds rainfall in poorly drained tidewater areas (Thorp and Smith,
The poor drainage, poor aeration, high salt content, recurrent
submersion, and high insolation on the vegetated parts of the flats
all serve to produce an intrazonal soil of a dark gray to yellowish
Solonchak type. On the nonvegetated, wind-deflated, playa portions
of the flats the soil is of an azonal, dark brown to gray, alluvial type,
originating from silts transported by the Rio Grande and its tribu-
taries and deposited on the flats during flood conditions. Salinization
of these sediments develops as a result of intermittent tidal flooding
and evaporation. On the lomas themselves the soil is also a halo-
morphic, azonal type, although its deposition is eolian. Farther inland
the major soil is Rendzina. This calcimorphic soil is developed
mainly from a limestone parent material (Brambila, 1957).
CLIMATE. The climate of the lower Rio Grande Valley is humid
and subtropical, characterized by relatively warm temperatures in
all seasons. Winters are usually short and mild. High summer tem-


peratures occur for long periods with readings near 1000 F. common.
Norquist's (1941) synopsis of weather data compiled for more than
40 years at the Brownsville airport includes the following: mean
temperature ranges from 59.80 F in January to 83.60 F in July;

FIGURE 2. Topography of the Loma Tio Alejos, southeastern Cameron County,
Texas. The major study site is typical of the clay dunes in this
region. Contour interval =2 feet.

Vol. 13


f ~- ~ ~ ~~.,'
I . 1





mean annual maximum temperature 98, mean annual minimum 300;
highest temperature ever recorded 104, lowest 120; mean date of
earliest killing frost December 26, latest January 30; mean length
frost free period 330 days. Some years are completely free of frost.
The mean July daytime temperature 1 inch above the surface at the
Loma Tia Alejos is 108.40 in the shade.
The mean annual precipitation in Brownsville is 26.3 inches. No
records are available for the eastern end of the Boca Chica Road,
but the study area is presumed to have as much, or perhaps more
rain than at the Brownsville airport. Though rainfall is erratic, most
of it normally falls in September (5.2 inches). In May, June, July,
August and October average rainfall varies from 2 to 3 inches. For
the remaining months the averages are less than 2 and more than
1.25 inches. The average spring precipitation (March-May) is 5.6
inches, summer (June-August) 7.2, fall (September-November) 9.0,
and winter (December-February) 5.3 inches. The average relative
humidity at the airport at 8 AM in January is 83%; in July 90%;
at noon in January 67%, in July 58%; at 8 PM in January 76%, in
July 70%. The study area is undoubtedly slightly drier than this,
and the potential evaporation ratio is certainly lower than 2.80 and
higher than 2.00. The prevailing winter winds are northerly; those
of the summer southeasterly.
VEGETATION. The vegetation of the lower part of the Rio Grande
Valley represents a southern extension of the semiarid, middle lati-
tude steppe characteristic of much of the western part of the Gulf
Coastal Plain. In the Holdridge life zone system the area is called
warm temperate subhumid dry forest, though edaphic features place
it close to thorn woodland. The present vegetation consists mainly
of dense shrubs, most of them thorny. This frost-conditioned grass-
land and brush, which Weaver and Clements (1938), call the Coastal
Prairie, they describe as "a chaparral-mesquite post climax of a
grassland climax," a cumbersome definition based on their assump-
tion that the local abundance of short grasses is a result of their
climatic dominance. It is now known that recent overgrazing has
favored the short grasses over taller grasses (Box, 1961). Kendeigh
(1961) places the region within the Aristida-Bouteloua association,
which he describes as the most arid of grasslands. His view that
overgrazing and fire control are responsible for the conspicuousness
of mesquite and cactus is shared by most ecologists familiar with
the area. Weaver and Clements (1938) regard the extension of the
mesquite brushland of southern Texas and northeastern Mexico in



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'~:F. hJi`~Cii~ ': *
~- ;;
r;~I ~a~-s~L .:1 .:I:;C
~ L-- *-
': ~'i`*.'J ~al?:~JI~S.-~

FIGURE 3. Outwash slope of Loma Tio Alejos looking westward over the flats
to the Loma de la Jauja. Vegetation with which Gopherus berlandieri
is most often associated in southeastern Cameron County, Texas:
A, buffalo grass, dead honey mesquite, and creeping mesquite in


Vol. 13




foreground; B, Berberus trifoliata right foreground, Baccharis texana
in middle; C, buffalo grass in foreground, Leucophyllum and dead
honey mesquite in middle; D, mixed, open bush.



the historical period as a pre-climax associes. Regardless of the com-
plexities of definitions reflecting the presumed ecological develop-
ment of the present vegetation, early explorers and naturalists de-
scribed the region as a vast grassland, with trees only along the
waterways (Havard, 1885).
Several different but related vegetational associations occur on the
lomas of the Jackass Prairie. To some extent they reflect successional
stages. The flora of the Loma Tio Alejos area is typical of the plain
and is described below (Figs. 3-6).
The most extensive plant cover on the flat loma top is a southern
Texas chaparral association, consisting of several species of thorny
shrubs and low trees. Dominant woody species include lotebush
(Condalia obtusifolia), honey mesquite (Prosopis glandulosa) and
huisache (Acacia farnesiana). Prickly pear (Opuntia lindheimeri), tas-
sajillo (Opuntia leptocaulis), lime prickly ash (Xanthophylum fagara),
and yucca (Yucca traculeana) grow along the edges of the thick
brush and in open patches. The association has few forbs. Grasses,
which are most abundant on the edges of the thick cover, include
three-awn grass (Aristida sp.), short grass (Bouteloua sp.), and sand
bur (Cenchrus sp.). Parts of the loma top are more open, with an
extensive grass cover dominated by buffalo grass (Buchloe dac-
The steep, eroding slope of the loma is a zone of an almost bare
sandy clay, variable in width, and supporting only a few woody
plants or shrubs such as creeping mesquite (Prosopis reptans var.
cinerascens) and prickly pear. Rapid runoff and low infiltration
rates on the slopes prevent most plant growth.
At the base of the erosional slope a gently sloping outwash plain
extends to the flat. Grasses are more extensive on the higher parts
of this slope than on top of the loma. The dominant grasses are sand
bur, curly mesquite (Hiliaria berlanderi) and buffalo grass (Fig. 3).
On the west side of the loma the outwash slope is broken by brush
clumps similar in composition to those of the loma top. On the
southeast side the open brush association is provided with an under-
story of windmill grass (Chloris verticillata), 3-awn grass, and sand
bur. With the exception of the northern end of the loma, the middle
portion of the outwash is covered with brush clumps composed of
lime prickly ash, granjeno (Celtis pallida), honey mesquite, lotebush,
huisache, agarito (Berberis trifoliata), prickly pear, tassajillo, and
creeping mesquite (Fig. 4). Leucophyllum frutescens occurs in
mixed and nearly pure stands in several places on the lower part of


Vol. 13

^ ~ ,, "-^ ..^ .-.. I ^ t -" *-

. *.
* kI; ,
it .- "

FIGURE 4. Loma Tio Alejos in southeastern Cameron County, Texas, looking
toward the central higher area of the loma. A, shallow wash, with
outwash slope in foreground and thick brush in background. B,
erosional bluff at top of the outwash slope; thick brush on top.


the western slope. At the periphery of the slope, and extending in

a narrow band around almost the entire loma to the elevation of the

surrounding playa flat is a zone composed almost exclusively of

JW a.-
''AL .0L
JIL JIL am JW & V, -
.. J L J JLJ M A L L & m LLA

A .06 is AL MyL
JA. JL .0

AL As A. M 1
~Y 1Yy
IY~Y 1Y ~Y As AL ~
J ca
Iyy y 1 1 J6 J" JL



FIGURE 5. Distribution of major plant associations on the Loma Tio Alejos in
southeastern Cameron County, Texas.

_ __ __ ________

__1 __



FIGURE 6. Distribution of dominant plants on the Loma Tio Alejos, southeastern
Cameron County, Texas. Zone A (flats with characteristic halophilic
plants): Atriplex matamorensis, Batis maritima, Monanthochloa lit-
toralis, Salicornia virginica, Suaeda linearis. Zone B (transition Zone
from outwash slope to flats): Borrichia frutescens. Zone C (outwash
slope): Aristida sp., Baccharis texana, Cenchris sp., Chloris verticil-
lata, Citharexylum berlandieri, Hiliaria berlanderi, Karwinskia hum-
boldtiana, Leucophyllum frutescens, Maytenus phyllanthoides, Plantago
sp. Zone D (includes plateau areas of loma and outwash slopes in
early stages of erosion): Acacia famesiana, Berberis trifoliata, Bu-
cheloe dactyloides, Castela texana, Celtis pallida, Condalia obovata,
Condalia obtusifolia, Dalia argyraea, Lycium berlandieri, Opuntia
leptocaulus, Opuntia lindheimeri, Pithecelobiam flexicaule, Prosopis
glandulosa, Prosopis reptans, XanthophyUum fagara, Yucca traculeana.

Baccharis texana (Figs. 5, 6).
Most of the plants growing on the flats are halophillic. The
dominant forms are soft grass (Monothochoa littoralis), salt wort
(Batis maritima), and Atriplex matamorensis. All of these extend
onto the lowermost portion of the outwash slope in favorable edaphic
situations. The lowest parts of the flats are covered with extensive
stands of Spartina. Many of the forbs and grasses die back during
unfavorable periods of the year when precipitation is low or grazing
pressure high. Only in spring when the cover of herbaceous vege-
tation is almost complete does the loma appear lush.
Essentially the same description applies to most of the lomas
nearby, but the windward sides of those lomas surrounded by
annually flooded, nonvegetated flats are presently accumulating wind-
blown silt which is gradually suffocating the typical loma vegetation.
The vegetation on these silt-covered areas is composed almost en-
tirely of widely scattered pioneer species, of which Croton argyran-



FIGmRE 7. Wind-blown silt and Croton argyranthemus on windward slope of
the Loma de la Lena Seca, in southeastern Cameron County, Texas.
Lomas are built from clayey silt deposited from flats such as those
in the background.

themus is most common (Fig. 7). Few grasses grow in the drift
On the younger, lower, but temporarily stabilized lomas, the
grass cover is fairly extensive. These grasses are mainly 3-awn,
panic, and sand bur. Shrubs and bushes, if present, are small and
widely scattered. Yucca and Opuntia often comprise the tallest
floral elements, though these too are widely scattered. These incipient
lomas are often comprised of low, parallel ridges and swales, the
former having a higher surface sand content than the latter (Fig.
8-A). The swales are seasonally flooded with brackish water. The
major vegetation in the swales are various species of brackish water
sedges, grasses, and succulents.
The area in which the study was conducted is a portion of the
broadly embayed coastal plain of the west coast of the Gulf of Mexico.
It lies within the meander belt of the Rio Grande and is a part of
that river's deltaic plain.
The developmental processes along this part of the western Gulf
are rather unusual in that alluvial deposition by the Rio Grande


Vol. 13


equalled the generally rising sea levels of the post-Wisconsin period.
Consequently the entrenched river valley was not drowned inland
from the continental hinge line, as were all the other large rivers
along the Texas Gulf coast (Deussen, 1924; Price, 1954).
Two high-standing sea level substages are well recorded in coastal
southeastern Texas. These are represented by the Late Pleistocene
Beaumont plain and the Recent alluvial, deltaic, and interdeltaic
depositional plains. The geological processes resulting in the forma-
tion of both these plains are very similar, differing only in their
geologic age and stages of maturity (Weeks, 1945; Trowbridge,
The surface sediment of the study area is Recent Rio Grande
alluvium overlying the Beaumont Clay. The postglacial north-south
wandering of the easternmost end of the river, together with the
annual flooding of its delta in April and May, particularly the Jackass
Prairie, has been responsible for the deposition of this sediment.
The recent construction of Falcon and Elephant Butte dams has
largely prevented the massive annual flooding formerly characteristic
of the area. Previously such flooding brought considerable silt into
South Bay via several flood outlets north of the river. Historical
records indicate that approximately 200 years ago an arm of the
river emptied into South Bay throughout the year (Hedgepeth,
1953). In 1880 the mouth of the Rio Grande, then located near the
eastern end of the Boca Chica road, moved south to its present
position when hurricane waves built a sand bar over its former
mouth. Tidal circulation into and out of South Bay was at that
time still afforded by the old Boca Chica Pass, but when the Browns-
ville ship channel was dredged in 1938 the resulting spoil banks
closed off much of this circulation. Reduced tidal scour at Boca Chica
Pass and a later storm closed off the remaining circulation. As a
result the mean water depth of South Bay was lowered 21/ feet,
from 4 feet to 18 inches. Periodic redredging of the channel has
tended to reduce the water level even more (Breuer, 1962). The re-
sult of all these factors is that more alluvial silt is now exposed in
the playa flats of the southern part of South Bay than at any time
within the historical record.
When not covered with either water or vegetation the exposed
silt is easily removed by wind action. Strongest deflation of the flats
occurs in summer, when flocculated saline clay accumulates on the
lee shore of the playas and lagoons to build clay dunes (lomas)
under the strong southeast winds characteristic of the area during











"C i


Vol. 13




Cu 0





this time of the year. Coffey (1909) and Huffman and Price (1949)
describe similar eolian-deposited clay dunes near Corpus Christi,
Texas, and have estimated that approximately one-fifth of the wind-
blown clay excavated from the playa lagoon basins is caught on
the dunes. The remainder passes inland as dust. Initially the silt
apparently accumulates in low parallel ridges with swales between.
The main axes of the ridges lie perpendicular to the prevailing wind
direction. The eastern end of the Mesa del Gavilon is typical of this
developmental stage (Fig. 8-A). These are the youngest habitable
surfaces available to the tortoises of Jackass Prairie.
The ridges and their vegetation serve as windbreaks, trapping
silt in the lee swales. Thus at a fairly early developmental stage
the parallel ridge and swale structure is replaced with a low dune.
Extensive dune growth depends on the continued availability of
source materials from the nonvegetated playas windward of the de-
veloping dunes. -If the flats or playas become vegetated, thus
anchoring the silt, the dunes are temporarily stabilized regardless
of their stage of development. Under these conditions northerly
winds, tides and rain tend to erode the loma to the base level of the
plain, eventually producing the low profiles seen in the lomas along
the Washington Beach Road, east of Matamoras, Tamaulipas, Mexico
(Fig. 8-G). These are the oldest habitable surfaces for tortoise
populations on Jackass Prarie.
Subsequent loss of vegetation on the playas through massive silt
deposition during river flooding results in the rejuvenation of dune
formation, ending the predominantly erosional part of the cycle. The
temporarily stabilized dune surface is then covered by another layer

FIGURE 8. Hypothetical development of the lomas in the study area, south-
eastern Cameron County, Texas. Lomas begin as a system of parallel
ridges and swales (A), which act as a windbreak and accumulate
wind-blown silt (closed arrows), rapidly assuming typical loma pro-
file (B). If flats surrounding loma remain free of vegetation, loma
continues to accumulate wind-blown silt (C and D, also see Fig. 7).
If flats become vegetated after continued absence of salt water, lomas
become temporarily stabilized, and erosion exceeds deposition (E,
open arrows). Old lomas in advanced stage of erosion are shown in
G and J. River or storm flooding may reduce vegetation on flats
initiating new deposition cycle (F).
Lomas of study area on the south side of South Bay, (E, F) have
gentle windward slope and steep lee slope from prevailing southeasterly
wind and seasonal tidal erosion of north end. Lomas on north side of
South Bay (H, I, J) near Port Isabel, have steep windward slopes cut
by deep erosional gullies from year-round presence of wave and tidal
action of lagoons on southeast side.


of wind-blown silt. Loma de la Lena Seca, just north of the Boca
Chica highway approximately 4 miles from its terminus, is in this
stage of development (Fig. 8-F). That dune coverage may be very
rapid is shown by the fact that during a period of 4 years a silt
blanket about 3 feet thick moved approximately 700 feet northwest-
ward over one part of the Loma de la Lena Seca, or about 175 feet
per year. This was established by comparing the extent of silt
coverage in 1962 as shown by aerial photos of the loma taken with
the limits of silt coverage established by direct observation in 1966.
The cyclic history of deposition on the lomas may be seen in the
clearly marked bands exposed in roadcuts and eroded bluffs. The
top of each band represents a stable, vegetated period. Such a
history of erosional and depositional cycles has tended to keep the
lomas in a dynamic equilibrium between pioneer successional plant
stages and, as shown below, affects the behavior of tortoise popula-
tions inhabiting them.
Before dissection by erosion, the lomas are characterized by a
gentle windward slope and a steep lee slope. In the southern
portion of South Bay these lee slopes become more precipitous,
with bluffs of 10 to 20 feet facing the bay. The formation of these
bluffs is a result of several processes: (1) the prevailing southeasterly
wind and its effect on dune cross-section; (2) differential rates of
erosion on the windward and lee sides of the dunes resulting from
differences in degree of slope; arid (3) tidal and wave erosion on
the north side of the dunes as a consequence of the northerly shift
of the winds during the winter months and the resultant periodic
flooding of the playas by tidal water (Fig. 8-E, F).
On the north side of South Bay the windward slopes of the lomas
are steep and cut by erosional gullies. The rapid erosion on the
windward instead of the lee side of these dunes undoubtedly results
from wave action and tidal oscillation in the lagoons located south-
east of these lomas (Fig. 8-H, I, J).
During the study we were able to observe a number of nest
features of Gopherus berlandieri not previously reported and to
gather information from both captive and natural situations. In the
only other report of nest building in G. berlandieri Sabbath (1960)
reported that a female dug a hole 3 inches deep and 13/ inches wide
into which she played 1 egg. In the present study we watched two

Vol. 13


captive tortoises dig nests, but none in the wild. The captive speci-
mens, collected near Sinton, Texas, were kept in a large outdoor pen
in Colorado.
Under the north side of a bush in the center of a circular enclosure
22 feet in diameter female A, carapace length 156 mm, built two
shelters (called pallets, see section on shelters), to one or the other
of which she retired each evening. At 07:45, 12 June 1961 she
scraped the bare floor of the pallet occupied the previous night by
using her epiplastral projection as a scoop. Starting at the pallet's
shallow end she moved to the deep end pushing a small amount of
dirt in front of her (Fig. 10-A). At the far end of the pallet, with
the plastron still on the ground, she twisted her shell from side to
side and moved laterally some of the dirt she had scraped up. She
then used her front feet alternately to push the dirt either outside
the pallet or onto her carapace. She then backed into her original
starting position at the shallow end of the pallet and repeated the
entire sequence. In 30 minutes she deepened the pallet's far end
about 1/2 inch.
She now turned in the pallet to face the opposite direction and,
with the rear portion of her shell in the lowest end, started to dig
the nest with her rear limbs. Alternately she placed each hind leg
medially under the plastron. As she drew the leg back to its normal
position the outer edge of the plantar surface picked up a small
amount of dirt and deposited it forward and laterally (Fig. 9). After

nest dirt --_


FIGURE 9. Major steps in nest construction by female Gopherus berlandieri.
A. scraping out the nest ramp. B. nest excavation, showing major
foot movements, body and limb positions, and ramp and nest spoil
areas. C. nest excavation, showing hind limb movements in pushing
dirt onto nest spoil areas.



repeating the scraping movements 2 to 4 times, she shifted the rear
of her shell in the direction of the leg last used, thus bringing the
opposite leg over the nest.
By 09:00 she was removing less dirt with each stroke. First the
shape of the cavity itself made digging more difficult. The hole was
now so deep that she had to draw each foot vertically to the surface,
and she could bring up little soil on the foot in this manner (Fig.
9-B). Secondly the soil became increasingly hard with depth. This
she partially overcame by urinating into the cavity. Bladder release
seemed to be correlated with digging activity, for she dug more
rapidly immediately after urinating, and the increased tempo re-
moved considerably more earth. Also of help was the moist soil,
which stuck better to the edge of her foot. As the soil again became
dry the digging tempo decreased. Previous authors (Woodbury and
Hardy, 1948; Carr, 1952; et al.) have attributed to urination during
nest building solely a soil-loosening function. We noted that urination
also helps by making the soil adhere better to the clublike feet.
The completed cavity was about 21/4 inches deep and 11/ inches
wide at the surface and had its greatest diameter 2 inches below the
surface. One egg was deposited in the nest at 09:23.
Though this was the only egg this female laid in the summer of
1961, on 28 March 1962 two eggs were found in a cavity in the same
pallet. It is not known if the same female dug this nest, as several
others were kept in the same enclosure. The nest cavity measure-
ments were: greatest depth 21/2 inches; greatest width 21/2 inches;
diameter of opening 11/2 inches.
At 08:00, 26 July 1961 female B (carapace length 186 mm) was
noted sniffing the virtually bare patches of soil around the peripheral
drip zone of a bush in an outdoor enclosure 12 feet in diameter in
Boulder, Colorado. By 08:30 she had scraped one of these spots so
that one end of the small cleared area was 1/2 inch lower than the
other. Unfortunately a subadult Gopherus polyphemus then pushed
her from the site and started to enlarge the deeper end, presumably
to begin burrow construction. Although the G polyphemus was re-
moved from the enclosure, the female G berlandieri did not resume
nesting operations that day.
By 09:15 the next day she had built an identical clearing and
slope immediately beside the pallet in which she normally rested.
The deepest end was 3/4 inches below the ground surface. Though
no actual digging was noted until 12:15 that day, the nest cavity
created in that time contained one malformed egg and some tortoise

Vol. 13


feces. Two days later this cavity was filled with earth, apparently
by the same female.
On 17 June 1962 the same female scraped a second "nesting
ramp" a few inches on the other side of its pallet. She began ex-
cavating at 08:10 and by 10:15 had deposited three eggs in a cavity
2 inches deep, 23/4 inches at its greatest diameter, and 134 inches
in diameter at the surface. One of the eggs was at the very top of
the nest cavity, the other two on the same plane at the bottom.
Captive tortoises often lay their eggs on the ground surface or on
the floor of the cage, presumably because the proper nesting medium
is lacking. Strecker (1929) reports finding 3 eggs under a tortoise
in the field on ground so rocky that a nest could not have been dug.
Grant (1960) reports finding 3 eggs on the surface on successive days
after the same female had laid 3 eggs in a nest a few weeks previously.
Once we found a single infertile egg on the ground surface in an
opening in the brush cover on the Loma de la Estrella. Several
nearby nest sites had already been destroyed by predators. The egg
did not hatch when artificially incubated, nor did two other eggs
found on the ground surface immediately adjacent to a pallet on the
Loma Tio Alejos. We saw no cavity and the eggs seemed undis-
turbed by predators.
Several factors may influence the choice of nest site: (1) soil
texture, (2) soil moisture, and (3) orientation with respect to the
sun. Data gathered on these in the field permit the following general-
1. The nest is normally constructed in soil relatively free of vege-
2. The nests are usually located under or near the drip zone of
3. No correlation is evident between nest site and the shade
pattern of the bushes (Fig. 10).
4. A positive correlation exists between density of nest sites and
density of tortoises, at least on the Loma Tio Alejos. Females use
no specific nesting areas.
5. Nests usually occur in small clusters (Fig. 11), with consider-
able distance between clusters regardless of tortoise density. It is
not known whether these clusters represent a series of nests dug by
one, or by several females.
6. Nests are often found near, and even in the same spot under
a particular bush in successive years. On the Loma de la Estrella we
found four destroyed nests under a prickly ash in November 1963



W 1
5 E

3 0

FIGURE 10. Thirty Gopherus berlandieri nest sites on the Loma Tio Alejos in
southeastern Cameron County, Texas, and their location with respect
to the closest shrub. Three nest sites were found near the shrub

where we had found two in June 1962. It is not known if these
nests were dug by the same female (Fig. 11).
Tracks in the soil near destroyed nests show that skunks and
raccoons prey on tortoise eggs. Neotoma micropus, the southern
plains woodrat, may also be an egg predator. Although, we have no
direct evidence, the foreman of a nearby ranch told us of seeing them
carry tortoise eggs in their mouths. That the woodrats do not use
the eggs to enlarge their debris homes is clear, as we found no egg
shells in these accumulations.
Predation data from a Gopherus polyphemus study (M.S.) in Lake
County, Florida suggest that nests destroyed before hatching are
usually lost within the first week following egg deposition. The same
may be true in populations of G. berlandieri in Texas. Scents asso-
ciated with nest building and egg laying are probably more important
in leading predators to a nest than the scent of the eggs themselves.

Vol. 13


^ ^^^^^.^^^>^ .. .-1962

southeastern Cameron County, Texas; A. around a shrub clump, 6
November, 1963; B. around a single Berberus trifoliata in 1962
and 1963. White circles = 1963 nests, dark circles = 1962 nests.

These associated scents probably disappear or become masked after
a few days. We found one fully formed dead hatchling G. berlandieri
in the field near a broken egg shell.
Very few nesting dates for berlandieri are available. Published
records for egg laying are 22 June (Sabbath, 1960), and 8 July
through 13 July (Grant, 1960). Additional information is now avail-
able. On 26 April 1966 we found several small holes on the Loma Tio

Alejos that appeared to repri neset trial nest sites. Similar excavations
were found there and on other lomas in August 1966. Freshly caught
captive females laid from 8 June to 2 August. The earliest date we
noted predator-destroyed nests in the field was 10 June, though
some of these, judging by shell membranes that had already dried
and fallen from the shell, were obviously several days old. Two eggs
with shells were found in a female accidental killed in November
1965 during National Guard maneuvers in the study area. Shells
found on the surface during the second week of November were
obviously the result of predation on recently laid eggs. Freshly
caught females sacrificed in the laboratory contained shelled eggs as
late as 16 September, and ovarian eggs larger than 10 mm in diameter
as late as November; this shows nesting dates in southern Texas
range from at least 8 June to 17 September.


Shelled eggs have been found in the oviducts as early as April,
and eggs 10 mm or larger as early as March. Ovarian eggs were
present in sacrificed females in March and April and again in
September through November. Two mature females sacrificed in
June and July had no ovarian eggs. The number of specimens sacri-
ficed to determine egg content was small, and by itself inconclusive.
These data, plus field observations, suggest two peaks in the produc-
tion of both shelled eggs and egg laying, one in late June and July,
the other in late August and September.
Whereas one to three eggs constitute the normal nest compliment
range, individual females may lay several clutches each year. Grant
(1960) reports that a captive female laid three eggs in a nest on
8 June, and later deposited single eggs on the surface on 19 June,
9 and 13 July. Under normal conditions this female probably would
have built at least two nests. None of the eggs hatched. This infor-
mation suggests that the previously mentioned clustering of egg sites
may reflect multiple nesting of individual females. If so, some females
must lay at least four clutches per year. It is not known whether
each female lays every year, on in alternate years.
Data on the number of eggs per nest laid by individual females
are available from three sources: (1) the number of eggs per nest
estimated from the broken shells found at nest sites in the field; (2)
the number laid in captivity; and (3) oviductal examination of females
sacrificed in the laboratory.
We recorded in the field a total of 88 nests represented by egg
shells only. Most had been excavated and destroyed by predators,
but some apparently had hatched. We assumed that egg remains
consisting of two or three large fragments more or less in place in
the nest site represented a successful hatch. Similar egg fragmen-
tation has been recorded after hatching in captivity. Scattered egg
fragments and such signs of predator intervention as digging were con-
sidered to represent unsuccessful nesting (Fig. 12). The number of
eggs could reasonably be established in 60 of these nests: 38 nests
contained one egg each, 19 contained two eggs and 3 contained
three eggs. Of 13 clutches laid in captivity 8 had one egg each,
4 had two eggs, and 1 had three eggs. The combined wild and
captive records are: 46 clutches of one egg, 23 clutches of two eggs,
and 4 of three eggs. Data on numbers of eggs per clutch laid by
other species of the genus are much the same. Miller (1932)
suggests that the nests of G. agassizi contain only one egg, but Grant
(1936) and others show the normal compliment varies from one to

Vol. 13


In general, the color pattern is similar to that of hatchlings of
G. polyphemus and agassizi, but darker (Agassiz' figured specimen is
even darker). Pigmented areas of the shell are dark brown, un-
pigmented areas creamy white. The unpigmented areas on the
anterior marginals are restricted to the posterior edge of each scute,
to the free edges on the lateral and posterior marginals, and to the
center of each costal and vertebral scute (smaller area than in any
specimens of polyphemus and most specimens of agassizi seen). The
plastral pigment is restricted to the scute seam areas except on the
femoral scutes, where pigment covers all but the free lateral edges.
The head has a yellowish stripe running from below the anterior
corner of the eye to the angle of the jaw. The tympanic region is
unpigmented. There is a faint yellowish temporal patch, also a
small unpigmented spot around the egg tooth and both nostrils. The
throat and chin are creamy white with a dark spot at the mandibular
symphysis. The horny mandibles are dark, and the remainder of the
head is dark brown. The scales at the base of both fore and hind
feet are black. The dark scales on the hind feet continue back
around the lateral side of the heel and up the hind leg for a short
distance, with the remainder of the hind leg a creamy white, except
for the yellowish thigh scales. The dorsal tail surface is grayish.
The outer brachial scales are black, while those of the middle
anterior portion of the front limb have light yellowish centers; those
of the inner edge are completely cream white. The scales of the
posterior brachial surface are dark on the dorsal half of the brachium
and lighter below, with the skin color of the upper and lower arm
sharply differentiated just above the elbow.
The proportions and shape of the hatchling berlandieri differ
somewhat from those of agassizi and polyphemus, but resemble
agassizi more than they do polyphemus (Table 1).

Characters berlandieri agassizi polyphemus
Gular scute Greatly projected Intermediate Not projected
Laminal spurs Absent Absent Present
Marginal denticulations Absent Absent Present
Head width Narrow Narrow Broad
Posterior plastral lobe Short, wide Longer Longer
Pigmentation Extensive Intermediate Proportionately
to little' very little2
1See Miller (1932) for variation data.
2Slightly darker on west coast of Florida peninsula and in Appalachicola River valley. See
Arata (1958) for variation data.



six. In G. polyphemus the number of eggs per nest varies from two
(W. A. field notes) to seven (Carr, 1952).
Measurements in mm of nine shelled eggs of G. berlandieri are:
48.3 X 32.4; 43.6 X 35.0; 53.7 X 32.6; 52.2 X 32.2; 46.5 X 35.6;
47.4 X 34.3; 48.2 X 35.6; 49.0 X 33.8 and 47.4 X 34.8
(width/length ratio 0.61 to 0.80, mean 0.71). Grant's (1960) meas-
urements of 6 eggs from Hebbronville, Texas are similar (width/
length ratio 0.66 to 0.82, mean 0.73). Sabbath (1960) described a
single egg of similar size (46 X 32). The eggs of G. agassizi and
G. polyphemus are generally more spherical (Grant, 1936; Carr, 1952).
Almost no information is available on hatchlings of G. berlandieri.
Agassiz (1857) figures a specimen (pl. III), but does not describe
it in the text, other than mentioning its dimensions (41 X 41 mm).
Woodbury (1952) figures and briefly describes a presumed hybrid
of berlandieri X agassizi that resulted from a mating described
earlier by Householder (1950). Hatchlings of agassizi have been
described by several authors (Woodbury, 1931; Miller, 1932; Grant,
1936; Woodbury and Hardy, 1948; et al.). Those of G. polyphemus
have been described by Allen and Neill (1953), Neill and Allen
(1957), and Arata (1958). The hatchlings of G. flavomarginatus
are unknown. A hatchling berlandieri (UF 23943, 40 X 41 mm)
found dead on the surface at Mesa del Gavilon (Fig. 13), but
associated with a broken shell, was obviously very close to hatching
or had just hatched. Its description follows:

FIGUBE 13. Hatchling Gopherus berlandieri (UF 23943), Mesa del Gavilon, 14
miles E. Brownsville, Cameron Co., Texas.

Vol. 13


The umbilical scar is just disappearing in a 48 mm specimen
(UF 16565, Zavala County, Texas), collected approximately 6 months
after the latest probable hatching date.

G. berlandieri is the smallest of the four extant species of Gopherus.
Beyond this, little is known of the species' size characteristics. Our
size data reveal differences in tortoise populations of reasonably
closely situated, but individually isolated lomas.
Secondary sex characteristics are clearly evident only in berlandieri
larger than 105 mm. Males attain a greater size than females, as
clearly illustrated by the Loma Tio Alejos population where males
averaged approximately 81/2% larger than females (Table 2). Essen-
tially the same relationship occurs in populations on the Port Isabel
Loma (males 8% larger) and the Mesa del Gavilon (males 9%

Parameter Loma Tio Port Isabel Mesa del
Alejos Loma Gavilon
Per cent adult males 27.7 46.6 20.0
Per cent adult females 57.6 53.4 40.0
Per cent nonadults 14.7 40.0
Average shell length
of females 140.8 mm 148.4 mm 166.7 mm
n=36 n=8 n= 10
Average shell length
of males 167.0 mm 195.5 mm 183.7 mm
n=75 n=7 n= 5

larger) though the sample sizes for each of these populations are
much smaller. The Loma Tio Alejos individuals are similar in size
(Fig. 14) to more inland populations near Laredo, Alice, San Diego,
and Sinton, Texas. Individuals from the Port Isabel Loma and Mesa
del Gavilon are larger than the Loma Tio Alejos specimens. The
largest specimen of this species reported so far is 214 mm in shell
length (Carr, 1952). As discussed later, many of the Port Isabel
males are younger than smaller male specimens on the Loma Tio
Alejos; the size differences are apparently due to differential growth
rates on the different lomas. The three largest specimens we have
measured, all males, are UF 18101, near Odem, Texas, 219 mm, and


Vol. 13


LLJ 30-X


75 105 135 to0 wO3
FIGURE 14. Size distribution of Gopherus berlandieri, Loma Tio Alejos, south-
eastern Cameron County, Texas. N = 130, class interval 15 mm.
Carapace length in mm.

UF 19562 and UF 23036, both from near Brownsville, Texas 218.2 mm
and 217 mm. The largest ones that Carr (1952) reports have all
come from southeastern Texas.

Determination of actual growth rate in nature demands data of
a type and quantity unavailable to us in our studies, but the rate of
growth can be estimated from the several recognizable size classes
within the smaller individuals of the population. The carapace
length at hatching is approximately 50 mm. No growth is evident
beyond the central areolae of each scute. The next size class ranges
from 70 to 81 mm, and these specimens show only one noticeable
growth ring beyond the areola, suggesting they are one year of age.
The mean size increase in the first year after hatching is 50.3%. This
increase is smaller than that calculated (68.1%) for the first year of
growth in Terrapene ornata (Legler, 1960). Identification of larger
size classes and correlative examination of major growth rings in
these classes suggest that sexual maturity is attained at from 3 to 5
years of age (Fig. 15), or from 105 to 128 mm. None of the tortoises
larger than this can be placed in distinctive size groups, although
many larger specimens show major annual growth rings. This sug-
gests that the growth rate slows markedly at about 6 years of age
(shell length about 130 mm) and thereafter remains more or less






75 100. 125 150 175

200 215

o 0 0
0 0
0 0 'b
o o <

5 10 15
FIGURE 15. Average annual percentage growth rate for G. berlandieri on the
Loma Tio Alejos in southeastern Cameron County, Texas.

constant at approximately 5% per year (Fig. 15). The maximum
number of major rings counted in any specimen was 18 (201 mm), but
the number can not be counted accurately in most specimens larger
than 180 mm.

The average absolute growth for males is 7.9 mm per year and
12.5 mm per two years, for females 11.1 mm per year and 18.9 mm

_ I i ii i I


Vol. 13


for two years, suggesting that females may grow slightly faster than

As in many other organisms color and size are related in ber-
landieri, and a general relationship between size and age may also
be assumed. To obtain data on the relationship between color, size,
and age, the frequency of tortoises in each of three color groups
(black and yellow, brown, and yellow and brown) was plotted against
size. Black and yellow tortoises are more common from hatching
through the 140-160 mm size range. The 160-180 mm size range
shows a pronounced increase in the number of brown individuals.
The brown and yellow individuals represent a transitional color phase
between a black and yellow pattern and a solid brown color, and
occur most frequently in the 140-160 mm size class. This was one of
several reasons influencing our division of tortoises into two size
groups (<150 and >150) in the movement section. Thus we regard
young tortoises as including both black and yellow and brown and
yellow individuals. Sexually mature individuals are found in all three
color classes. That black and yellow individuals may be sexually
mature is attested by the fact that some of them breed and lay eggs.
Old tortoises are always a light brown or "horn" color.

Only for the Loma Tio Alejos are the data sufficient to provide
more than a rough estimate of population density. Data for analysis
are based on 193 tortoises known to live on the loma. As the area of
the entire loma is approximately 85,500 square meters, the minimum
overall density is 430 square meters per tortoise. As we found a few
unmarked tortoises on every visit, the actual density is probably
slightly greater than this. Nonetheless we believe that the total
counted is close to the actual total for the loma. We assume that
the unmarked tortoises are not immigrants from other lomas primarily
because of the distances such moves would involve and the lack of
shelter from the sun in the intervening flats. Reasons for considering
the populations of each loma as more or less isolated are discussed
more fully below.
Even casual observation makes it obvious that the tortoises are
not evenly distributed on the loma. Therefore we determined tor-
toise density in each of the characteristic plant associations of the
loma. Only the first sighting of each tortoise was used in the analysis,


regardless of season, year, or activity of the individuals. Thus each
tortoise was for purposes of density estimates counted only once,
regardless of where it was subsequently recaptured on the loma. Of
the four major plant associations on the loma, tortoises are most
dense in the brushy area (Table 3), although considerable variation
Plant associes Area (M2) Number Density
Brush 9,750 119 1:82 M2
Baccharis Zone 7,500 25 1:300 M2
Grass and Cactus 48,000 39 1:1,231 M2
Clay Zone 15,750 10 1:1,575 M2
Totals 85,0001 193 1:430 M2
1Includes approximately 4,500 M2 of brush too thick to be investigated.
occurs within each of the associations. For example, tortoise density
in the brush on the outwash slope (1 tortoise per 64 M2) is much
greater than in the brush on top of the loma (1 tortoise per 1429
M2). We have no evidence of seasonal variation in these densities.
Though definitive data are lacking, tortoise densities for corres-
ponding plant associations on adjacent lomas are probably com-
parable. However densities on the open eastern end of the Mesa
del Gavilon are lower than on any comparable area on the Loma Tio
Alejos. Careful search revealed only three tortoises on its small,
sparsely vegetated area. On the Port Isabel Loma the difference
between the high tortoise density on the middle of the lee slope
and the very low density at its base is marked, though the plant
association is continuous. On the Loma de la Lena Seca tortoises
wander far over the windblown silt in search of food. Population
density on the silted area is very low, though in the adjacent brushy
areas it is probably comparable to that of the brush on the Loma
Tio Alejos. In the open drier brush complex of Falcon Dam State
Park, Starr County, Texas, we estimated the density to be about 1
tortoise per 42,000 square meters.

From November 1963 through April, 1966, 159 tortoises were
marked on the Loma Tio Alejos by drilling 1/8 inch holes in the
peripheral bones according to a 6-digit code. Data recorded upon
capture and recapture included time of day, location, activity in
which the tortoise was engaged, color of cloacal discharge, sex, and


Vol. 13


carapace length. After coding and recording data at the place of
capture the tortoises were released. Thus the captured and recaptured
data represent known geographic point occurrences of each tortoise.
In order to indicate the place of capture more accurately, the loma
was marked off in a grid of 50-meter squares. The location of each
tortoise was first determined as to square, and then within each
square by obvious landmarks. The original location of the tortoise and
those of subsequent recapture were transferred to a large-scale map
of the loma, based on topographic maps (Palmito Hill Quadrangle,
U. S. Geol. Surv.), available high altitude aerial photos (S. E.
Cameron County, map 6, U. S. Dept. Agric.), and low-level aerial
photos taken by the senior author. Movement between captures was
measured on the map as the straight-line distance from the original
point of capture. This method of determining movement was selected
because we felt it would be a better test of the reality of the activity
range of the type described in Chrysemys scripta (Cagle, 1944),
Terrapene (Stickle, 1950; Legler, 1960), and Gopherus agassizi
(Woodbury and Hardy, 1948).
The recapture data were analyzed in three ways: accumulative
movement between 1, 2, and 3 years; movement per trip; and move-
ment per day. Within each category the data were analyzed according
to sex and size. Data on daily movements were obtained by using
a spool and thread trailer similar to that described by Stickle (1950)
(Fig. 16), and by following tortoise tracks in the sand or silt. The
analysis of accumulative annual movement was designed arbitrarily
to compare the movement of two size classes of tortoises; those
greater and those less than 150 mm in carapace length.
Table 4 shows that tortoises 150 mm or shorter move farther than
larger ones. No correlation is evident between sex and distance

berlandieri ON THE LOMA Tio ALEJOS
Shell length Sex 1 year 2 years 3 years
150 mm > Males 98.6 (12)1 153.0 (8) 130.0 (5)
Females 94.1 (13) 92.4 (11) 164.1 (6)
Means 96.6 (25) 118.0 (19) 149.0 (11)

150 mm < Males 30.0 (2) 149.1 (3) 178.0 (1)
Females 93.7 (19) 162.0 (11) 302.0 (6)
Means 87.5 (21) 159.5 (14) 284.0 (7)
1Figures in parentheses are recaptures per visit.


FIGURE 16. Daily movement data were obtained by means of a thread trail,
released by the mechanism pictured.

traveled. All tortoises tend to move away from the original place of
Records of daily movements (Fig. 17, Table 5) indicate a tendency
to maintain a temporary activity range. Of eight turtles tracked by
a thread trail, three (field numbers 321, 104, 203) returned within
2 days to the pallet in which they were originally captured, and one
(field number 21) returned to the same bush in which it was originally
captured but to a different pallet. Only one (field number 331)
showed no definite tendency to maintain a restricted activity range
during the observation period. Those tortoises with activity range
(approximately= home range) indices approaching or exceeding
unity are regarded as having a weak tendency to maintain an activity
range. The average maximum distance traveled per day was 20.6
meters and the average distance of the night pallet from the original
was 8.3 meters. The patterns in figure 17 reinforce the thesis that
the tortoises, while nomadic, maintain restricted activity ranges for

Vol. 13



FIGURE 17. Typical daily movements of six Gopherus berlandieri, Loma Tio
Alejos. Solid and dotted lines represent successive days. The small
hemispheres represent pallets used. Data gathered by thread trails.
See Table 5.

short periods of time. The average observed distance tortoises traveled
during an average visit (1 week, Table 6) is intermediate between
daily and yearly average distances. These tortoises are therefore
primarily nomadic, and maintain restricted activity ranges for only
a few days between successive greater or lesser secondary movements.
In addition to tracing movements on the Loma Tio Alejos, we
also followed tortoise movements on several other lomas in various
stages of plant succession and geological development. Our findings
suggest that daily movement at least is influenced by the successional



Table 5. DAILY MOVEMENT OF Gopherus berlandieri ON THE LOMA Tio ALEJOS
Max straight Pallet
Tortoise Shell length line distance distance Home range
number (in mm) Sex (in meters)1 (in meters)2 index3

321 22.0 21.3 0.97
21.3 0.0 0.00
104 113 ? 15.5 0.0 0.00
15.8 0.0 0.00
21 120 9 10.7 4.6 0.37
10.7 1.5 0.14
331 152 42.6 42.6 1.00
52.5 95.0 1.81
51 159 9 5.2 4.8 0.92
303 159 16.4 7.9 0.48
304 168 12.2 7.0 0.57
203 171 9 18.9 0.0 0.00
1Distance moved from original pallets.
2Distance between new and original pallets.
3Maximum straight line distance/pallet distance.

stage and geological age of the loma. For example, the tortoises on
the Loma de la Lena Seca, on which wind-blown silt is currently
being deposited, move greater distances per day than tortoises on the
other lomas studied. The tracks four tortoises made in a single day
across the wind-blown silt measured 46.0, 161.0, 142.0, and 480.0
meters. The mean distance of daily movement for three accumulative
years on the Loma Tio Alejos is 267.0 meters. The reason for these
movement differences between tortoises of the two lomas obviously
is related to food availability. The accumulating silt has suffocated
much of the vegetation and hence food, on the Loma de la Lena
Seca (Fig. 7).

(mm) 1963 1964 1965 1966 1966a Means

150> 42.8(10)' 178.0(4) 86.0(2) 151.0(3) 32.7(3) 86.2(22)
150< 36.8(10) 41.7(8) 55.5(5) 32.5(1) 60.5(4) 55.7(28)
Means 39.8(20) 104.9(12) 79.8(7) 91.8(4) 46.6(7)
'Figures in parentheses are recaptures per visit.

Vol. 13


Daily activity periods recorded for April, June, and July show
that the tortoises have two principal activity periods, one in the
morning, and one in the afternoon. Table 7 shows the tendency for
activity periods to become better defined in June and July. By July
(and August, according to unrecorded data that admittedly are open
to subjective bias) most tortoises are active in the afternoon after
15:00 or 16:00. We found no differences in activity period with
respect to size or sex.
Subjective observations for November (1963) suggest that the
daily activity pattern resembles that available for April (1966) in that
we made more midday and fewer late afternoon and morning obser-
25-29 April 10-13 June 13-17 July 9-22 July
Time of day 1966 1966 1964 1965 Totals
05:00-07:00 0 1 3 0 4
07:01-09:00 2 7 15 15 39
09:01-11:00 15 1 0 4 20
11:01-13:00 6 0 0 0 6
13:01-15:00 0 0 0 0 0
15:01-17:00 11 0 3 17 31
17:01-19:00 0 1 28 14 43
19:01-21:00 0 0 0 1 1
Totals 34 10 49 51 144

In June 1966 we performed several preliminary field experiments
to test the ability of G. berlandieri to recognize a home range and
orient within it. We released tortoises at various distances and
directions from the pallets in which we found them and traced
their movements for 36 hours by means of a thread (Fig. 16). We
made 5 releases on the Loma Tio Alejos and 11 on the adjacent flats
away from typical tortoise habitat (Tables 8 and 9; Figs. 18 and 19).
Releases on the loma reinforce the daily movement data that suggest
a temporary activity range (Fig. 17). The cues the tortoise uses to
recognize its activity range remain unknown, but are presumed to
be visual or olfactory landmarks. That local features may aid a
tortoise to recognize its activity range is suggested by the movements
of tortoises released on the featureless flats. These showed no con-
sistent ability to reach the loma from two release points 50 and 125




Vol. 13


Distance removed
from pallet
(in meters)



Compass direction





Distance from pallet
at end of test
(in meters)









Table 9. HOMING ABILITY OF Gopherus berlandieri RELEASED ON FLATS
Distance released Final distance Final heading
from loma from loma (+ =toward loma,
(in meters) (in meters) = away from loma)
108.5 155.0
108.5 0.0 +
93.0 0.0 +
87.0 87.0
108.5 54.4
108.5 0.0 +
108.5 136.4
105.0 0.0 +
54.5 82.2
54.5 54.4
49.6 65.2

be partly responsible for the disorientation shown by tortoises released
on the flats. We found no evidence that tortoises regularly cross
the flats from one loma to another, or that they even make short

S 100o M

FIGURE 19. Thread trails of 10 Gopherus berlandieri released on the flats west
of the Loma Tio Alejos, southeastern Cameron County, Texas. The
tortoises had no consistent ability to reach the loma (brush symbols
to right) when released approximately 50 and 100 meters from the
loma edge. Dots indicate the final resting place of the tortoises.
See Table 9.



forays onto the flats from a "home" loma. On the contrary we found
that tortoises avoid wandering onto the flats at all. On the Lomas
de la Lena Seca and de las Vacas tracks are easily followed over
wind-blown silt. We tracked many tortoises from the central vege-
tated parts of the loma to the loma-flat border and then back onto
the loma. Several tracks paralleled the loma edge one for several
hundred meters. Only one tortoise wandered out onto the adjacent
flat, and then only for a distance of about 10 meters before turning
Wandering over the flats from one loma to another would usually
be fatal to a tortoise because of the lack of shade, and could only be
done in cool, cloudy weather. Obviously such trips have been made
in the past, as tortoises occur on most of the lomas. We do not
believe, however, that these populations were seeded primarily by
any tendency of the tortoise to wander onto and over the flats. The
seasonal flooding of Jackass Prairie by the Rio Grande before the
Falcon and Elephant Butte dams were built may have been an
important means of transporting tortoises from one loma to another.
That flooding can displace tortoises without fatal results is shown
by populations of G. agassizi near Tucson, Arizona, whose members
often survive being swept considerable distance by seasonal flooding
of the arroyos along which they live.
The geological history of the Jackass Prairie shows that in
advanced stages of loma erosion the raised level of the intervening
flats is modified through deposition. The raised level of the flats
encourages the growth of larger, shade-producing plants and reduces
the density of halophytic vegetation. These changes would improve
the chances of successful dispersal across the flats. Thus more fre-
quent interloma exchange is expected over the older, more vegetated
and consequently more stable flats, than over the lower, seasonally
innudated, geologically younger, and vegetatively barren flats pres-
ently being deflated by wind erosion.

Over most of its range G. berlandieri spends almost all of its
resting periods in a form or pallet it makes by scraping away the
ground litter and soil over an area slightly larger than itself, normally
at the base of a bush, under a cactus clump, or a tuft of grass. In
the following account the anterior end of the pallet is the end that
projects into the ground and against which the tortoise rests the
front of its shell. This is usually little more than a sloping ramp the

Vol. 13


tortoise makes by using the epiplastral projection, the front limbs,
and the lateral edges of the shell. Within the activity range of almost
every individual are several active, cleaned-out pallets, as well as
a number of old, trash-filled ones. Recapture and thread trail records
show that the individual tortoise uses several of the pallets within
its daily activity range. The directness with which tortoises walk
to particular bushes under which active pallets are located within
their activity ranges suggests that they know the exact location of at
least some of these pallets.
Anteriorly the pallet is usually deep enough to conceal the dorsal
front edge of the tortoise's shell (Fig. 20). Before using an unoccu-
pied pallet, the tortoise often pushes out the accumulated soil and
vegetable matter. The continued use and clearing of specific pallets
tends to deepen them, and some much-used pallets in the Brownsville
area become deep and overhanging enough to cover the entire tor-
toise. The deepest pallet we found on the clay lomas was approxi-
mately 13 inches long and 4 inches deep at its anterior end. Such
deepening may be fairly rapid. One pallet with a 1-inch overhang in
1962 was extended by an unknown number of tortoises to an 8-inch
overhang by 1963.
The literature on the use of burrows as opposed to pallets by
G. berlandieri is not conclusive. Carr (1952) states that though
G. berlandieri burrows have been reported, he found none in the
clay soils of Tamaulipas, Mexico. True (1882) doubted that the
species ever used burrows. Grant (1960) reported on correspon-
dence received from V. M. Lehman, Wildlife Manager of the King
Ranch, Kleberg County, Texas, who stated that though tortoises are
often found in burrows in the local sandy soils, he doubted that the
tortoises excavated them; rather, he believed that they simply utilized
existing burrows of large mammals. At Falcon Dam we found the
tortoises using both the holes made by coyotes digging for rodents
and the dens of armadillos. Our evidence suggests that while tor-
toises do use mammal burrows, they can and do excavate their own.
We found one tortoise burrow that was approximately 4 feet long
and 1 foot deep in a caliche soil 5 miles west of San Diego, Duval
County, Texas, 18 June 1965; fresh tracks from this burrow led us
to the animal. In sandy soil 3 miles north of Laredo, Webb County,
Texas on 16 June 1966 we found two holes with the typical hemis-
pheric cross section of Gopherus diggings; one was 2' 10" and the
other 4' 3" long, both were about 12 inches below the surface at
their deep ends. Though the Laredo burrows were empty, their


2 'U !V

-.'.;: .U .. "".i"
-%' ~:b ,
FIGURE 20. Top. Gopherus berlandieri in a typical pallet, Mesa del Gavilon
southeastern Cameron County, Texas. Bottom. Same pallet empty.

Vol. 13




entrances suggested recent use. In both areas we found normal
pallets. That these burrows were used solely as winter shelters is
doubtful. Possibly such burrows are used more commonly in the
northern than in the southern portions of the species' range, but Guy
Austin, Curator of Reptiles, San Antonio Zoo, told us he knew of no
tortoises in that area that dug or retreated to burrows at any time
of the year. He reports that in winter they simply "shuffle themselves
down into the soil until the shell is about an inch or two below the
surface." Grant (1960) describes similar winter activity in this species
near Hebbronville, Jim Hogg County, Texas. Immediately after a
northerr" in November, 1961, we found a tortoise on the surface
near Sinton, Texas that had just extricated itself from such a depres-
In August 1966 we found two tortoises in burrows they themselves
had obviously dug in sandy soil on the eastern part of the Mesa
del Gavilon, several miles east of the Loma Tio Alejos. One, an
adult female, was in a burrow 33 inches long and about 12 inches
deep at its end below a small clump of Opuntia (Fig. 21). That this
burrow had been used for a long time was suggested by trails leading
away from it through the surrounding three-awn grass that were
practically identical to trails leading from the mouths of established
burrows of G. polyphemus. The second specimen, a juvenile, was
in a small burrow 71/2 inches long, excavated under a board lying
on the ground surface.
Near Brownsville we found pallets and short burrows in the
accumulated rotten cactus pads of old and active Neotoma nests. One
short burrow extended into the almost disintegrated base of a rotten
mesquite stump. Carr (1952) collected specimens under stumps and
rubble heaps in Tamaulipas, Mexico.
These records suggest that G. berlandieri is highly opportunistic
regarding use of shelter. In sandy soils, where holes are easily ex-
cavated, and where the lack of shade in summer or the cold of
winter encourage such activity, some individuals may dig a burrow.
In other regions, such as the low sandy lomas near the Boca Chica
beach, individuals possibly spend much of their lives in such burrows.
In still other areas, such as San Diego and Laredo, burrows may be
used intermittently or only in the winter. In all parts of their range
the tortoises modify the burrows of other animals and use any other
available shelter such as old, or even active, pack rat houses. It is
perhaps significant that deep burrows are not excavated into poorly
drained soils, such as clay. Because the major soil type within its



FIGURE 21. Entrance of Gopherus berlandieri burrow, approximately 1 meter
long, in sandy soil, Mesa del Gavilon, southeastern Cameron County,

range is a type of feldspathic clay, the species usually constructs a
pallet rather than a burrow for shelter. In some regions these pallets
may be deepened in the winter to cover most, or all of the shell.
A similar behavioral variation in the excavation and use of shelters
is known in both G. agassizi and G. polyphemus (Auffenberg, in
press). The factors governing the type and use of shelters by popu-
lations of all three species are (1) the extent of seasonal extremes
in surface temperatures, and (2) substrate composition.
On 11 November 1963, we measured 92 active pallets and short
burrows on the clay soils of the Loma Tio Alejos in two dimensions:
1) the extent of the overhang at the deepest end and 2) either the
length of the tortoises found in the pallet, or if empty, the width of
the pallet. The width measurements were converted to approximate
tortoise shell lengths. That the width of a tortoise's burrow or pallet
is approximately equal to the tortoise's carapace length is the basis


Vol. 13


of the conversion. The data for pallet depth, as measured by the
extent of the upper overhanging lip, shows that pallet overhang is
negatively correlated with tortoise length. In the Loma Tio Alejos,
juvenile tortoises tend to dig a proportionately deeper pallet than
larger animals (Fig. 22). Tortoises less than 100 mm long character-
istically dig a pallet longer than their own shell length, with one
exception- a juvenile found wedged under the fallen trunk of a
honey mesquite. Of 10 juvenile tortoises in the size range 60-100 mm
found in pallets, all but one had pushed dirt behind them plugging
the opening to their short burrow. This dirt plug is probably im-
portant in both water balance and predation. In the most arid parts

M 60


W 30


75 125 115

FIGURE 22. Carapace length and relative pallet overhang of G. berlandieri on the
Loma Tio Alejos in Cameron County, Texas. Pallet overhang/cara-
pace length ratios as follows: 0-1.0, white column; 1.1-2.0 solid
column; 2.1 and over, crossed column.
column; 2.1 and over, crossed column.



of agassizi's range adult individuals also make similar plugged bur-
rows in the exceedingly hot and dry summer months.
Pallets are usually in a slight depression, against the side of a
small surface irregularity, or against the base of a tree, shrub, or a
cactus pad. We have seen tortoises enlarging both active and non-
active pallets made by smaller individuals. One tortoise dug a pallet
in a small depression one of us made a day earlier when searching
for very small tortoises. Another was seen enlarging the deepest part
of a cow hoof print for its pallet.
Some evidence indicates that pallet use is seasonal. Pallets in the
thick brushlands on the Loma Tio Alejos definitely are used through-
out the year, but in summer (June, 1966) proportionately more
tortoises are found in pallets in the thick brush than in open areas.
In winter (November, 1963) a greater proportion of tortoises are
found in pallets in open brush or grassy areas (November: 16 in
pallets located in thick brush, 24 in open brush or grass; June: 19
in pallets in thick brush, 10 in pallets in open brush or grass).

Data on feeding and food preferences in G. berlandieri are avail-
able from both field and laboratory studies. Table 10 summarizes
identified plant remains from droppings collected in the field during
August 1966, most of it composed of several types of grasses. In the
wild we have seen tortoises eat the feces of other tortoises and of
rabbits. In captivity we have also observed them eating the grass-
filled droppings of their own and other tortoise species. In addition
to the plant remains listed in Table 10, one crayfish claw, several
broken land snail shells, and a few fragments of beetle elytra have
been identified in the feces.
Country people living in the range of G. berlandieri are well aware
that one of the commonest plants these tortoises eat is the cactus,
Opuntia, a food preference also reported in the literature (Grant,
1960; Mittleman and Brown, 1947; et al.). Of the two species of
Opuntia found in the immediate study area, 0. lindheimeri is eaten
more often. The tortoises feed on its pads, fruits, and flowers. Pads
knocked to the ground by grazing cattle are often eaten before they
become desiccated. The tortoises also eat the upright, growing pads
along their lower edges when within reach. We have seen individuals
with their noses nearly covered with the small areolar spines of this
cactus, and some on their tongues as well. We found several indi-
viduals with large spines working their way out of the masseter


Vol. 13


+, abundant; L, leaves (some stems); F, fruits.

berlandieri POPULA-

Loma de la Mexican Loma Tio Port W. end,
Lena Seca Loma' Alejos Isabel Mesa de
Loma Gavilon
Opuntia lindheimeri L+, F+ L+, F+ L, F L+, F+
Opuntia leptocaulus F
Grasses (Bucheloe,
Chloris, and Aristida) L, F+ L+, F+ L+, F+ L+, F+ L+, F+
Cenchris F F F
Plantago F
Monothochloa L
Prosopis reptans L
Citharexylum L, F
Xanthophyllum L+ L+ L+, F+
Condalia obovata L L+ L
Celtis pallida F F
Berberis L
Lycium L L
Maytenus L
Viola sp. F
Aster sp. F
ISample considerably less than from remaining areas.

muscles on one or both sides of the head. One specimen that died
in captivity had its small intestine completely blocked by a small
cactus pad that was still spiney.
The fruits of both Opuntia lindheimeri and 0. leptocaulus are
eaten either red (ripe) or green. Ripe fruits not eaten by other
animals eventually fall to the ground, and these the tortoises seem
particularly partial to. The fruits and pads are an important source
of water as well as nutrition. Opuntia lindheimeri flowers occur in
two color varieties on the Loma Tio Alejos, yellow and reddish
orange; we have seen tortoises eating both.
While Opuntia is eaten commonly, its use is somewhat seasonal
in the study area. When the lomas are lush with the spring rains in
April, grass is the most common food. Opuntia lindheimeri is eaten
increasingly in the summer when the grass starts to wither. Though
the pads are available throughout the entire year, cactus flowers
appear only from June through August. The fruit of the previous
year begins to ripen in June and by July becomes a major part of the
tortoise diet. At approximately the same time the "urine" changes
color from a murky brownish-red or clear yellow to clear red, re-



fleeting the dietary change to ripe Opuntia lindheimeri fruits. The
fruits of Opuntia leptocaulus normally ripen in October and Novem-
ber, and they are eaten mainly during this period.
Other food habits and/or preferences seen in G. berlandieri in-
clude biting the bleached bones of cows and rabbits on several
occasions. Carr (1952) reports similar behavior in G. polyphemus
in Florida. Herbivore nutritionists associate this with diets low in
phosphate rather than in calcium as commonly believed. Captive
G. berlandieri accept a great variety of fruits and vegetables if not
too tart or bitter. Lettuce supplemented with bone meal and occa-
sional fruits seems an excellent and easily obtained diet for captive

Grant (1960) notes that G. berlandieri shows a decided preference
for red-colored food, and he relates this preference to the ripe fruit
color of Opuntia lindheimeri. The senior author initiated in 1964 a
broader study of color preferences in various populations of all species
of Gopherus, the results of which are to be published later. The
color preferences shown by G. berlandieri are included here for the
sake of completeness.
Two groups of six adult males and six adult females each were
tested for color preferences in two periods: 1 May to 28 June, 1964,
and 2 August to 5 October, 1965. The testing device was, a series of
three metal tabs each colored differently with electrical current-
conducting Dykem Metal Dyes, (Dykem red, blue, and light green),
and connected to a Grayson-Stadler "Drinkometer" vacuum switch
requiring 0.6 millivolt for circuit closure. Each vacuum switch was
connected to an electric digital counter. The switches were fastened
inside a container on the floor of the pen housing the tortoises. A
wire guard over the metal tabs prevented accidental contact. A tor-
toise could make contact only by deliberately placing its head
through the spaces in the wire guard and touching the tab. The
linear sequence of the three colored tabs was changed every 5 days
during each of the two experimental periods of 30 days each. Table
11 shows the results obtained during the two test periods.
These tests reveal that (1) red and green are bitten more often
than blue, supporting Grant's contention, and (2) the 12 tortoises
caught in the spring and tested in May and June bit the green tabs
proportionately more than the 12 specimens captured in the summer
and tested in August and September. The shift to red in the labora-


Table 11. SEASONAL COLOR PREFERENCE OF Gopherus berlandieri
Test period Red Blue Green Totals
May and June 96W 13 121 280
August and October 192 48 22 262
Totals 288 61 143 492
xNumber bites per color tab.

tory experiments is in accord with field observations on food color
changes. During the summer ripe red cactus fruits are substituted
for the green grass of the spring. The relatively large number of
responses to blue during the August-October tests is perhaps ex-
plained by the presence at this time of the year of ripe bluish-black
fruits such as those of Citharexylem, which the tortoises are known
to eat.

Little is known about post-hatchling predation on this species:
Predation pressure on adults is probably rather low. One adult female
found dead on the Loma de la Estrella in November 1963 obviously
had been dragged out of its pallet, killed, and eaten the preceding
night. The only carnivores in the area large enough to accomplish
this feat are coyotes and bobcats. Though the inhabitants of Port
Isabel claim one jaguar lives in the general area, it is said to stay
usually near the coast north of the ship channel. Pieces of tortoise
shell are often seen in the rubble houses of the southern plains wood
rat, Neotoma micropes. That the wood rats kill the adults is doubtful,
but they may be the most important single predator on hatchlings
in view of their apparent predation on eggs. On the other hand,
juveniles, and particularly hatchlings, are probably often eaten by
most carnivorous animals large enough to break away the shell.
This category includes foxes, coyotes, skunks, bobcats, and raccoons.
The remains of one tortoise no more than 1 year old found on the
surface of the Loma Tio Alejos (UF 21914) lacked the rear third
of the shell and body; the predator remains unknown. In Florida
adult indigo snakes (Drymarchon corais) are known to feed on hatch-
ling G. polyphemus (pers. comm., Robert Mount). This snake is
reasonably common on the lomas of the study area and may repre-
sent still another source of hatchling predation. The same species
of snake eats hatchling red-legged tortoises (Geochelone carbonaria)
in Panama.



Human activity is without question the most important single
factor affecting the distribution and population density of G. ber-
landieri. Many of man's effects are direct, such as the removal and/or
Killing of individual tortoises or populations, but probably even more
important are his indirect effects by habitat destruction or modifica-
tion. In southern Texas the shift from cattle raising to field crops,
particularly cotton, destroyed thousands of acres of the region's unique
brushlands. Mexico has a long history of severe overgrazing, a
practice that continues to destroy additional thousands of acres of
tortoise habitat.
The next most important factor is undoubtedly the automobile.
Untold hundreds of tortoises are killed on the highways of Texas
and Mexico every year, many deliberately. Perhaps the most dis-
tressing activity is the collection and sale of hundreds of specimens
for the pet trade. Though better adapted to captivity than other
species of Gopherus, individual G. berlandieri seldom live long out-
side their normal range, and most individuals slowly starve on a diet
of insufficient variety to supply their mineral and vitamin require-
ments. Many ranchers deliberately kill the tortoises because of a
mistaken notion that they break or eat quail eggs. Fortunately the
State of Texas has recently passed legislation protecting G. ber-
On the positive side are several human activities favoring the
tortoises, the most important of which is probably the effect of
managed grazing in tortoise habitats, as discussed in preceding sec-
tions. Even more dramatic, but longer range effects can be seen in
brush control areas where successional development of the mesquite-
chaparral community' is maintained as a vegetatively ecotonal area.
This practice, while initially killing many tortoises, increases grass
production, and under current brush control practices the scattered
brush cover the tortoises need reappears very quickly. If, in addition,
the area is grazed by cattle, it is maintained in a dynamic equilibrium
in which tortoises maintain their maximum densities over long periods
of time. Slight overgrazing under such conditions encourages the
growth of the prickly pear, Opuntia, one of the staple foods of G.
berlandieri when grasses become dry in the summer.
Perhaps the most important contribution of our studies on Go-
pherus berlandieri is the behavioral variability demonstrated between
the populations in the study area. Such variability is surprising in

Vol. 13



view of the relatively short distances between the lomas to which the
tortoise populations are restricted. At the root of the behavioral
differences lie differences in the geological and vegetational histories
of each of these lomas. The major differences in interpopulational
behavior, such as shelter construction, activity range, and food pref-
erence are all closely interrelated.
The tortoises of the genus Gopherus are characteristically found
in the arid and semiarid portions of southern United States and
Mexico. Here where water, food, and shade all are often scarce,
tortoises are able to survive more by their ability to modify regula-
tory behavioral patterns than on their physiological limitations. Not
the least important of their homeostatic activities is the ability of
individuals of all four species to escape critical temperatures and
humidities by excavating a simple shelter of some type.
Of the nine living genera of tortoises only Gopherus includes
species that habitually dig long, deep burrows in the ground,
(Auffenberg, in press). The front limbs of the extant species are
specialized for this purpose to varying degrees. The most specialized
limb is found in G. polyphemus in which the feet and forelimbs are
remarkably flattened and spade-like, with stout, relatively immovable
digits provided with robust, flattened claws. Whereas the wrist of
most other tortoises can be moved to a limited degree, that of
G. polyphemus is made largely immovable by strong, sheet-like lig-
aments that bind the bones into a more or less solid unit (Auffenberg,
1966). Thus the limb is functionally a small spade, providing the
tortoise with an effective soil-moving device. Of the living species
of Gopherus the limbs of berlandieri are the least specialized for
G. polyphemus is an essentially non-nomadic species that usually
lives on sandy soil in ecotonal situations where it usually digs a
long, unbranching burrow (Fig. 23). Though these tortoises live
in what appears to be a dry habitat, the end of the burrow is
generally moist. This moisture is apparently one of the most impor-
.tant of the factors determining the depth of excavation (Hansen,
1963; et al). Although evidence shows that new burrows are some-
times excavated, each individual normally uses a single burrow
throughout its life with the burrow diameter and length increasing
with the animal's growth. The tortoises leave their burrows almost
every day to graze on the vegetation found within several hundred
feet of the burrows.
This behavioral pattern is not characteristic of all the populations



"-" r 1

. % . i!I
FIGURE 23. Entrance of typical burrow of Gopherus polyphemus, Astor Park,
Lake County, Florida.

throughout the species' range. For example, in at least one area in
Levy County on the west coast of Florida some individuals do not
dig burrows, but shelter themselves in a shallow form or pallet under
a tuft of grass or bush. The region these tortoises inhabit is warm
throughout most of the year. The substratum is moist; the land
surface is just a few feet above sea level, and only a few inches of
soil overlie the limestone bedrock. Still another atypical situation
is represented by some individuals on Marco Island, Collier County,
Florida where a single individual may use both burrows and pallets,
the pallets apparently on warm, moist nights and the burrows the
rest of the year.
In the relictual grasslands of the interior drained Bolson de
Mapimi at the junction of the Mexican states of Durango, Chihuahua,
and Coahuila, is a second species of burrow-digging tortoise, G. flavo-
marginatus. Recently discovered and poorly known, this species is
similar to G. polyphemus in both morphology and habits (Legler,
1960; Legler and Webb, 1961; Auffenberg, 1966). During the Pleis-
tocene its range extended approximately 300 miles south of its present
southern limits in Mexico, and north at least to southern New Mexico.
Thus its present distribution is only a small remnant of a range

Vol. 13



that previously embraced almost all the Mexican plateau. The bur-
rows of this species extend into the hard, baked soil of the playa
basins to depths of at least 8 feet. Like G. polyphemus, the Mexican
bolson tortoise grazes along feeding paths leading from the burrow
mouth through the surrounding grasses.
The third species is the desert tortoise, G. agassizi, of south-
western United States and northwestern Mexico, which has the largest
range of all the Gopherus species. The great variety of soil types
and temperatures included in its range are reflected in the ecological
behavior of the constituent tortoise populations.
Individuals living at the southern edge of the species' range in
Sonora, Mexico, are completely nomadic throughout most of the
year. The activity range of individual tortoises is apparently very
large, though mostly restricted to the dry arroyos that dissect the
region. The shelter most commonly used is a shallow hollow dug into
the base of the arroyo wall (Fig. 24). Several individuals use the
hollow during a season. Each occupant enlarges it slightly by scraping
at the walls for a few moments before settling for the night.
The pattern of shelter construction and use by individuals of the
same species in the rocky arroyos of Pima County, Arizona, is
similar, except that the lower winter temperatures demand more
protection. Hibernation takes place in specific shelters to which
individual tortoises often return year after year. These hibernacula
are always located well above the arroyo floor and are usually simply
an enlargement of a ground squirrel burrow. Normally the excavated
enlargement extends only deep enough so that the rear portion of
the tortoise's shell is flush with the arroyo wall. This is apparently
enough to remove the tortoise from the cold night winds and yet
exposes a part of its shell to the afternoon sun.
Because these hibernation sites are usually on south-facing arroyo
slopes, and because the tortoises enlarge the burrows of local
mammals able to excavate their own galleries only in certain kinds
of bank strata, the number of available over-wintering sites is limited.
This factor frequently leads to winter aggregations of tortoises in
Arizona, where four or five individuals are "parked" in adjacent
"garages" during the colder months (Fig. 24).
Still another behavioral pattern has been described for populations
at the extreme northern edge of this species' range in southeastern
Utah (Woodbury and Hardy, 1948). Here the tortoises have two
distinct activity ranges a large warm weather range on the desert
flats where they excavate short burrows in the shallow soil, and a



Upper. Pallet scraped into arroyo wall by Gopherus agassizi near
Aduana, Sonora, Mexico. Lower. Individual G. agassizi hibernacula,
near Tuscon, Pima County, Arizona.



r ~I -'

~ t Z
b~ ..~tY~
~ a


much smaller, cool weather range near the winter dens at the upper
reaches of the arroyos emptying onto the flats. Thus their activity
range shifts toward the flats in early summer and toward the foot-
hills in late summer. The greatest distance covered during this
annual movement is not known to exceed 2 miles.
The hibernating burrows of the Utah tortoises differ from those
farther south in several respects. They are communal and may
contain as many as 23 individuals. The burrows attain a length of at
least 33 feet, and are frequently divided and anastomosed within,
often with multiple openings to the outside (Fig. 25). Each year
these dens are slightly enlarged by the scraping of the tenant
tortoises preparing for hibernation. The dens are usually on south-
facing slopes, generally above the floor of the arroyo, and always
in a somewhat cemented gravel.
In both Arizona and Utah the hibernacula are associated with
rodent dens. That this is a common and probably important associa-
tion is fairly clear. It was presumed formerly that the ground
squirrels invaded the burrows the tortoises excavated. Studies by the
senior author in other parts of southern United States clearly demon-
strate that the reverse is the case though pack rats often move in
The colder winter temperatures of Utah require longer burrows
than in Arizona. Thus it is likely that the anastomosing dens of
G. agassizi in Utah are simply an extension of the Arizona hiber-
nation situation where the tortoises lie at separate enlarged entrances
to a rock squirrel den, but do not enlarge the tunnelways to the end
of the rodent labyrinth as they do in Utah. The communal nature
of the Utah hibernacula is to be expected in a region that offers
fewer sites for adequate winter protection.
In some parts of the range of G. agassizi, where winter tempera-
tures are sufficiently cool to require a long burrow and the soil is
easily excavated, individuals use a single burrow throughout the
year. The tunnel is deeper, but the burrow is otherwise identical
to those in Utah the same species uses only in summer (Fig. 25).
The regions in which such burrows are found seems to include all
the sandy areas in and surrounding the Mohave and Sonora Deserts
of California, Arizonia, and northwestern Mexico.
These observations suggest that at least C. agassizi and G. poly-
phemus are opportunistic burrowers and excavate a shelter to what-
ever depth is necessary or possible under prevailing conditions. This
behavioral variation is apparently a reflection of several factors. (1)



+ .- 3d
ri r"E


7y ..,.

cc~~ -..


jCounty, Utah.

'- . .

..* -. i. .

FIGuRE 25. Upper. Communal hibernating burrow of Gopherus agasszi Beaver
Dam Slope, Washington County, Utah. Lower Individual burrow
of G. agassizi excavated in sandy soil near Mesquite, Washington
County, Utah.

Vol. 13

'Pr :Wp~ :rg


the innate behavioral patterns of the species, (2) the local tempera-
ture extremes, and (3) the characteristics of the soil in which the
retreat is excavated.
As has been shown in the body of this paper, over most of its
range G. berlandieri has no permanent daily retreat that it uses all
year long. With the anterior projection of the plastron the tortoises
excavate a shallow form or pallet to which they may or may not
return regularly. Though usually little more than a sloping ramp,
a few old pallets have the deeper end overhanging enough to cover
the entire shell. During winter most individuals bury themselves in
the soil. This is the normal pattern on the clayey soils found
throughout most of the species' range. On the sandy, less vegetated
soils some berlandieri dig a longer burrow to which they probably
return most of their lives. Others often use burrows of other animals
when they are available. Thus this species is as opportunistic as the
other members of the genus in shelter construction and excavation.
The pallet of Gopherus, and particularly the burrow, has the
important function of regulating temperature and moisture, and varies
with the season in type, position, and use. In summer the adult
agassizi often plug their short burrows behind them, obviously an
important temperature and moisture regulating device in their desert
habitat (Woodbury and Hardy, 1948). We have shown that small
berlandieri tend to dig proportionately deeper pallets than larger
specimens and that they also frequently plug their burrows with
earth. In this case shelter depth and the earthen plug are probably
related to predation pressure on juveniles as well as temperature
maintenance and water conservation.
Our experience shows that of all the Gopherus species, polyphemus
desiccates most rapidly in captivity if deprived of a burrow, which
may explain why this species is so consistently associated with bur-
rows throughout almost all its range. The only places where indi-
vidual polyphemus do not dig a burrow are both warm and moist.
Territorial behavior in turtles and tortoises has not been widely
studied. None of the principal published studies (Stickel, 1950;
SWoodbury and Hardy, 1948; Legler, 1960; Cagle, 1944; et al.), with
the exception of Gould's work on Terrapene (1957), demonstrate
precisely defined territories or well established homing ability in
chelonians. G. polyphemus has a rather well-defined activity range
within which all feeding and reproduction take place. The popula-
tions of G. agassizi that retire to burrows instead of pallets show a
well-defined home range.


All the evidence available on tortoises indicates positive correla-
tion between individual burrow use and a well-defined home or
activity range. For example, throughout most of its range G. ber-
landieri is decidedly nomadic and does not dig burrows. Where it
does dig burrows, well-defined trails leading from their entrances
show a regular traffic to and from the burrows, in turn suggesting
these individuals have a more restricted activity range.
The mean daily movement of individual tortoises, regardless of
species, seems greatest in populations where the shelter is apart
from the feeding grounds, or where food plants are scarce or widely
scattered. Food is plentiful enough in most parts of the range of
G. polyphemus so that most individuals rarely have to move more
than 50 meters from their burrows to feed. On the other hand,
individuals of G. berlandieri living where food plants are widely
scattered may move as much as 400 meters in a day. Such a large
activity range is probably not found in those individuals that dig
their own burrows, as the extent of their movement is partly deter-
mined by the presence of a shelter to which they regularly return.
Populations of G. agassizi differ greatly in extent of activity range;
determined in part by the degree of dependence on a particular
shelter, as well as food availability.
No well-developed homing tendency has been demonstrated in
the pallet-inhabiting G. berlandieri, which probably reflects the rela-
tive homogeneity of the activity range with respect to food and
shelter. We expect the homing tendency would be better developed
in burrow-inhabiting individuals of the same species. The facts that
pallets may be used alternately by more than one individual, and
that daily activity ranges may overlap quite broadly suggest that
lebensraum in this species is not exclusive. Except for those popula-
tions whose members live in burrows, apparently very little com-
petition for space and shelter exists in the species.
The most important single factor in population density in G. ber-
landieri is habitat modification by man or other natural agencies.
'he greatest densities are reached in open brush associations, which
are essentially ecotonal. To this extent G. berlandieri is identical to
the other species of the genus, which also reach their maximum
densities in ecotones of a xeric nature.
Within rather broad parameters in the living species of Gopherus
the fluctuations in the limiting factors of the environment obviously
are not nearly so important as the species' regulatory behavioral
patterns. This is perhaps best shown in the variability of the type

Vol. 13


and utilization of shelter. Important in the exact expression of this
behavioral pattern are tortoise size, daily and seasonal climatic
changes, the extent of plant cover, soil characteristics, and availability
of previously excavated shelters of appropriate size and position.
The most significant aspect of the biology of G. berlandieri is its
behavioral plasticity. An unwritten, but usually implied premise of
life history studies is that the particular population studied is assumed
to model the behavior and life history of the entire species. We feel
that no more reason exists for this assumption than for assuming
morphological uniformity throughout the range of a species. In fact
the behavioral variation of G. berlandieri exceeds the demonstrated
degree of morphological variation in this species. Physiological
adaptations have certainly determined the range limits of G. ber-
landieri, and within these rather broad parameters the distribution
of G. berlandieri is a result of behavioral opportunism.
The evolutionary success of tortoises has never really been closely
assessed. The protection furnished by the shell is not unique to
these organisms. Many other animal groups have developed armor
just as effective and in many cases more protective. Nor is major
environmental variability an important factor in tortoise evolution.
The habitat of virtually all extant tortoise species is very similar,
being semiarid grassland or thorn brush. The present investigation
of G. berlandieri and the accompanying brief review of North
American tortoise ecology and behavior presents what we feel is the
real basis of evolutionary success witnessed in these organisms. This
success stems from a broad, nonspecialized, behavioral base allowing
the land tortoise maximum adaptive plasticity through flexible be-
havioral patterns in order to compensate for seasonal, climatic, and
geological changes in the environment.

Gopherus berlandieri populations on the isolated clay dunes
(lomas) near the mouth of the Rio Grande were studied intermit-
tently from 1961 to 1967. The conclusions resulting from this study
are as follows:
1. Nests are always excavated in well-drained areas, often under
the drip zones of shrubs and in sites relatively free of herbaceous
2. Nests are most common within the areas of greatest tortoise
density. Females do not move to special egg-laying areas.



3. Mature females probably lay several egg clutches each year.
The number of eggs per clutch varies from 1 to 3, mode 1.
4. The normal pattern of nest construction includes a preliminary
stage of nest ramp excavation.
5. Eggs are known to be laid usually from 8 June to 22 August,
though some may be laid as late as November.
6. Though raccoons, skunks, and opossums are known egg preda-
tors, the southern plains wood rat (Neotoma micropus) is perhaps the
most active and efficient predator on eggs.
7. In form and color the G. berlandieri hatchlings are more similar
to those of G. agassizi than to those of G. polyphemus.
8. Secondary sex characters are apparent at approximately 105 mm
in straight line carapace length.
9. Ontogenetic color and pattern changes are not correlated with
onset of sexual maturity.
10. The mean shell length of males is greater than that of females.
11. Growth-size increase is greatest the first year after hatching
(about 50%), decreases rapidly to sexual maturity at from 3 to 5
years (about 6%), and then slowly thereafter for a period of at least
18 years (about 5%). Females may grow at a somewhat faster rate
than males.
12. Mean size is known to vary between populations, probably in
response to differences in food and its availability, which are in turn
related to the recent geomorphic history of the lomas and human
13. Sex ratios vary from one population to another. The factors
governing this variation are not known.
14. Of the several vegetational associations on each loma, tortoise
densities are highest in open brush with an understory of grass
(1 tortoise: 82 M2). They are least dense in open grass or nonvege-
tated areas (1 tortoise: 1,575 M2). They do not live in the seasonally
flooded tidal flats between the lomas. The high density in open
brush is probably correlated with availability of both shelter and food.
15. Daily activity peaks occur in the morning and late afternoon
throughout most of the year. Bimodality in activity periods is most
pronounced in late summer when midday surface temperatures are
high. Unimodality in activity periodicity occurs on warmer days
during the winter.
16. No correlation exists between extent or periodicity of move-
ment and sex.
17. Small tortoises move greater distances than larger ones.


18. All individuals tend to maintain a small, temporary activity
range, broadly overlapping those of other tortoises, regardless of sex
or size.
19. The mean daily movement on the different lomas studied
varies widely, and apparently depends on food availability.
20. Yearly movement data show that almost all individulas have
a marked nomadic tendency, so that the entire loma may be con-
sidered an activity range.
21. Homing ability is not well developed.
22. The cues used in recognition of the transient activity ranges
are probably visual and based on local landmarks.
23. When released on the flats where they do not normally live,
in sight of the home loma, tortoises do not necessarily move in its
direction, and are apparently completely disoriented.
24. Little interchange of tortoises occurs from loma to loma.
25. Most individuals throughout the species' range excavate a
shallow form or pallet in which they spend much of each day and
the entire night. Several pallets may be used by one or more tortoises
within a particular tortoise activity range.
26. A short burrow is often made in exposed situations on sandy
soil. Burrows may be excavated by either the tortoise or by other
animals. In some regions burrows are used intermittently, in others
continuously. In poorly drained clayey soils, where winter tempera-
tures reach a critical lower limit, the tortoises simply "shuffle" them-
selves under the surface for protection from the cold.
27. Smaller tortoises tend to dig deeper pallets than larger ones,
and frequently plug them with earth behind themselves.
28. The use of pallets in exposed situations varies seasonally.
29. Most commonly eaten are the pads, flowers, and fruits of the
cactus Opuntia lindheimeri and various grasses. The diet varies
seasonally. Many different food items are identifiable by scat analysis.
Though essentially herbivorous, coprophagy is common. The young
are partly carnivorous, at least in captivity.
30. Food color preference is related to food experience, which
varies seasonally and geographically.
31. Predation apparently is highest on the eggs and young.
Predators rarely kill adults.
32. The most important single factor affecting tortoise density is
habitat modification by either man or natural geologic phenomena.




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