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Wildlife, Animals, and Plants
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Introductory
WILDLIFE SPECIES: Gopherus agassizii | Desert Tortoise
ABBREVIATION :
GOAG
COMMON NAMES :
desert tortoise
TAXONOMY :
The currently accepted scientific name for the desert tortoise is
Gopherus agassizii Cooper [6,23].
Three distinct populations are recognized: the population found in
California and southwestern Nevada; the population found in Arizona
south of the Grand Canyon; and the population found in southwest Utah,
Nevada, and Arizona north of the Grand Canyon [6].
ORDER :
Chelonia
CLASS :
Reptile
FEDERAL LEGAL STATUS :
Threatened
OTHER STATUS :
NO-ENTRY
COMPILED BY AND DATE :
S. A. Snyder, April 1991
LAST REVISED BY AND DATE :
NO-ENTRY
AUTHORSHIP AND CITATION :
Snyder, S. A. 1991. Gopherus agassizii.In: Remainder of Citation
WILDLIFE DISTRIBUTION AND OCCURRENCE
WILDLIFE SPECIES: Gopherus agassizii | Desert Tortoise
GENERAL DISTRIBUTION :
The desert tortoise inhabits southern Nevada, extreme southwestern Utah,
southern California, southwestern Arizona, and Sonora, Mexico [7,15].
ECOSYSTEMS :
FRES30 Desert shrub
FRES33 Southwestern shrubsteppe
STATES :
BLM PHYSIOGRAPHIC REGIONS :
7 Lower Basin and Range
12 Colorado Plateau
KUCHLER PLANT ASSOCIATIONS :
K039 Blackbrush
K041 Creosotebush
K042 Creosotebush - bursage
K043 Paloverde - cactus shrub
K044 Creosotebush - tarbush
K046 Desert: vegetation largely lacking
K060 Mesquite savanna
K061 Mesquite - acacia savanna
SAF COVER TYPES :
68 Mesquite
242 Mesquite
SRM (RANGELAND) COVER TYPES :
NO-ENTRY
PLANT COMMUNITIES :
Desert tortoises inhabit dry, flat, and gravelly or sandy ground in
desert shrub communities where annual and perennial grasses are abundant
[7,15]. Tortoises frequent habitats with a mix of shrubs, forbs, and
grasses. Some of these species include creosotebush (Larrea
tridentata), pricklypear cactus (Opuntia echinocarpa), banana yucca
(Yucca baccata), sixweeks grama (Bouteloua barbata), bush muhly
(Muhlenbergia porteri), and white bursage (Ambrosia dumosa) [22]. A few
tree species, such as Joshua tree (Yucca bevifolia) and mesquite
(Prosopis spp.), may be present also.
REFERENCES :
NO-ENTRY
BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Gopherus agassizii | Desert Tortoise
TIMING OF MAJOR LIFE HISTORY EVENTS :
Mating - Begins in May and continues at various intervals until autumn
Breeding age - 15 to 20 years
Nesting - Typically May through July; may nest in autumn
Incubation - 118 days
Clutch size - 4 to 13 eggs; may lay more than one clutch per season
Life span - 50 to 100 years
Hibernation - October through April; may estivate in shallow burrows
during the hot, dry summer months [2,7,13,17,19,22].
PREFERRED HABITAT :
Desert tortoises live in hot, dry desert shrub areas. They seek shade
under rocks or shrubs during intense heat [7]. In California, tortoises
frequent areas with high annual bloom potential and a diverse array of
perennials and cactus scrub. They are found at elevations between 1,000
and 3,000 feet (300-920 m) [13]. In the Mojave and Sonoran deserts
tortoise frequent steep, rocky slopes [6].
COVER REQUIREMENTS :
Desert tortoises dig burrows for winter hibernation and shallow holes
for summer estivation. The soil must be a fine gravelly and/or sandy
loam, with some clay for burrow stability [13,22]. Burrows are dug in
the open or under shrubs and rocks. They can also be found in the banks
of gullies and washes [2]. In addition to burrows, tortoises sometimes
rely on shrubs for cover during the day. In Arizona tortoises use rock
outcrops for burrows [16].
FOOD HABITS :
Desert tortoises are primarily herbivorous; they eat forbs, grasses, and
a few shrubs. The bulk of their diet consists of annual wildflowers,
annual and perennial grasses, perennial shrubs, and cacti. Some genera
include Astragalus, Camissonia, Coreopsis, Cryptantha, Erodium,
Euphorbia, Gilia, Lupinus, Malacothrix, Mentzelia, Phacelia, Plantago,
Bouteloua, Bromus, Festuca, Schismus, Sphaeralcea, and Opuntia
[2,10,22].
PREDATORS :
Desert tortoise populations suffer from a wide variety of predators,
most notably man. Grazing livestock can trample young and adult
tortoises both in and out of their burrows [2,19,21]. New hatchlings
are frequently taken by common ravens (Corvus corex) [1,6]. Other
animal predators include the desert bobcat (Lynx rufus baileyi), desert
coyote (Canis latrans estor), desert kit fox (Vulpes macrotis arsipus),
gray fox (Urocyon cinereoargenteus), badger (Taxidea taxus), western
spotted skunk (Spilogale gracilis), Nevada ringtail (Bassariscus astutus
nevadensis), and the golden eagle (Aquila chrysaetos) [22].
MANAGEMENT CONSIDERATIONS :
Desert tortoises can suffer from a highly contagious upper respiratory
disease which is capable of destroying entire populations. The disease
is thought to be contracted from tortoises kept as pets whose owners
have released to the wild [19].
REFERENCES :
NO-ENTRY
FIRE EFFECTS AND USE
WILDLIFE SPECIES: Gopherus agassizii | Desert Tortoise
DIRECT FIRE EFFECTS ON ANIMALS :
Brush fires can be lethal to desert tortoises because they move so
slowly. Fragments of tortoise shells have been found in burned areas
[22]. Tortoises usually estivate in burrows during the hot, dry summer
months when fires are more likely to occur. Therefore any direct fire
effects on tortoises may be minimal, although some smoke-caused
mortality is possible.
HABITAT RELATED FIRE EFFECTS :
The absence of literature dealing either peripherally or specifically
with fire effects on the desert tortoise may indicate that it has not
been a concern. Humphrey [11] stated that fires do not carry well in
the Sonoran and Mojave deserts, two areas where tortoises are
concentrated. These areas are dominated by widely spaced, open-branched
trees and shrubs. However, fire can carry well in areas with abundant
grasses and forbs, areas also frequented by tortoises. Bock and Bock
[5] reported that although more research is needed to determine the
effects of fire on wildlife in the Sonoran-Mojave desertscrub, in
general, fire is destructive to woody plants and cacti and does not
necessarily increase forbs and grasses. They see little benefit and
much potential harm to wildlife as a result of fire. However, they also
reported that in what was once the Sonoran savanna grassland (now
invaded by desertscrub), fire could be an important wildlife management
tool for restoring grassland [5]. Summer fires may be most detrimental
to the tortoise because they rely on dried grasses for forage during
this time. Winter fires may be less harmful because tortoises hibernate
then and are not dependent on available food [14].
FIRE USE :
Prescribed fire can be used to control invading shrubs and possibly
increase forage production. If used they should probably be conducted
during mid-winter. Tortoises are not dependent on forage then, and they
can avoid any direct mortality from fire. Tortoises display dramatic
changes in seasonal feeding behavior, which are greatly influenced by
temperature and moisture. Burning just before the rainy season may be
beneficial if forage is replaced during or towards the end of the rains.
Tortoises come out of their burrows at this time and depend on the
available grasses and forbs. In general burning should be very
carefully planned so as not to coincide with feeding seasons of the
tortoise. They feed in the spring and periodically throughout the
summer, during and following rainstorms. They also feed just before
hibernation in mid-October [14]. Bock and Bock [5] concluded that
prescribed fire frequency in the Sonoran savanna grassland should not
exceed postburn recovery time of forbs and grasses. Also, shrub and
tree cover should be maintained where they occur naturally.
REFERENCES :
NO-ENTRY
REFERENCES
WILDLIFE SPECIES: Gopherus agassizii | Desert Tortoise
REFERENCES :
1. Bernard, Stephen R.; Brown, Kenneth F. 1977. Distribution of mammals,
reptiles, and amphibians by BLM physiographic regions and A.W. Kuchler's
associations for the eleven western states. Tech. Note 301. Denver, CO:
U.S. Department of the Interior, Bureau of Land Management. 169 p.
[434]
2. Berry, Kristin H. 1978. Livestock grazing and the desert tortoise. In:
Transactions of the 43rd North American wildlife and natural resources
conference; 1978 March 18-22; Phoenix, AZ. Washington, DC: Wildlife
Management Institute: 505-519. [13693]
3. Berry, Kristin H. 1986. Desert tortoise (Gopherus agassizii) research in
California. In: Management of the desert tortoise in California:
Proceedings of the symposium; 1985 March 3-5; Malibu, CA. In:
Herpetologica. 42 (1): 62-66. [13697]
4. Biswell, H. H. 1958. The use of fire in California chaparral for game
habitat improvement. In: Proceedings: Society of American Foresters
meeting; 1957 November 10-13; Syracuse, NY. Washington, DC: Society of
American Foresters: 151-155. [12149]
5. Bock, Jane H.; Bock, Carl E. 1987. Fire effects following prescribed
burning in two desert ecosystems. Final Report on Cooperative Agreement
No. 28-03-278. Fort Collins, CO: U.S. Department of Agriculture, Forest
Service, Rocky Mountain Forest and Range Experiment Station. 20 p.
[12321]
6. Campbell, Faith Thompson. 1988. The desert tortoise. In: Audubon
wildlife report 1988/1989. New York: National Audubon Society: 567-581.
[13695]
7. Carr, Archie. 1952. Handbook of turtles. Ithaca, NY: Cornell University
Press. 542 p. [13691]
8. Eyre, F. H., ed. 1980. Forest cover types of the United States and
Canada. Washington, DC: Society of American Foresters. 148 p. [905]
9. Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; [and others].
1977. Vegetation and environmental features of forest and range
ecosystems. Agric. Handb. 475. Washington, DC: U.S. Department of
Agriculture, Forest Service. 68 p. [998]
10. Hansen, Richard M.; Johnson, Mark K.; Van Devender, Thomas R. 1976.
Foods of the desert tortoise, Gopherus agassizii, in Arizona and Utah.
Herpetologica. 32: 247-251. [13702]
11. Humphrey, Robert R. 1974. Fire in the deserts and desert grassland of
North America. In: Kozlowski, T. T.; Ahlgren, C. E., eds. Fire and
ecosystems. New York: Academic Press: 365-400. [1217]
12. Kuchler, A. W. 1964. Manual to accompany the map of potential vegetation
of the conterminous United States. Special Publication No. 36. New York:
American Geographical Society. 77 p. [1384]
13. Luckenbach, Roger A. 1982. Ecology and management of desert tortoise
(Gopherus agassizii) in California. In: North American tortoises:
conservation and ecology. Wildlife Res. Rep. 12. Washington, DC: U.S.
Department of Agriculture, Forest Servcie: 1-37. [13727]
14. Nagy, Kenneth A.; Medica, Philip A. 1986. Physiological ecology of
desert tortoises in southern Nevada. In: Management of the desert
tortoise in California: Proceedings of the symposium; 1985 March 3-5;
Malibu, CA. In: Herpetologica. 42 (1): 73-92. [13699]
15. Pope, Clifford H. 1949. Turtles of the U.S. and Canada. New York: Alfred
A. Knopf Inc. 343 p. [13692]
16. Schamberger, Melvin L.; Turner, Frederick B. 1986. The application of
habitat modeling to the desert tortoise (Goperus agassizii). In:
Management of the desert tortoise in California: Proceedings of the
symposium; 1985 March 3-5; Malibu, CA. In: Herpetologica. 42 (1):
134-138. [13698]
17. Stuart, George R. 1954. Observations on reproduction in the desert
tortoise Gopherus agassizii in captivity. Copeia. 1954(1): 61-62.
[13701]
18. Turner, Frederick B. 1986. Management of the desert tortoise in
California. In: Management of the desert tortoise in California:
Proceedings of the symposium; 1985 March 3-5; Malibu, CA. In:
Herpetologica. 42 (1): 57-58. [13696]
19. U.S. Department of the Interior, Fish and Wildlife Service. 1994.
Endangered and threatened wildlife and plants. 50 CFR 17.11 & 17.12.
Washington, DC: [Publisher unknown]. 42 p. [24413]
20. U.S. Department of the Interior, Fish and Wildlife Service. 1990. Final
listing rules approved for 14 species. Endangered Species Technical
Bulletin. 15(10): 11. [16592]
21. Webb, Robert H.; Stielstra, Steven S. 1979. Sheep grazing effects on
Mojave Desert vegetation and soils. Environmental Management. 3(6):
517-529. [4164]
22. Woodbury, Angus M.; Hardy, Ross. 1948. Studies of the desert tortoise,
Gopherus agassizii. Ecological Monographs. 18: 145-200. [13694]
23. Schmidt, K. P. 1953. A check list of North American amphibians and
reptiles. 6th ed. Chicago, IL: University of Chicago Press. 280 p.
[21123]
Index
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