General Distribution
The desert tortoise is widely distributed throughout the Mojave and Colorado deserts from
below sea level to 1250 m (4130 ft) or higher. It is most common in desert scrub, desert
wash, and Joshua tree habitats, but occurs in almost every desert habitat except on the most
precipitous slopes. Densities range from 3.5 per km 2 (9.2 per mi 2) in the eastern Mojave to
more than 1000 per km 2 (2600 per mi 2) in the western Mojave near California City (Stebbins
1954, Marlow 1979). Habitat Requirements
This species normally excavates a burrow under bushes, overhanging soil or rock
formations, or digs into the soil in the open. Burrows are most extensive in the northern part
of the range where winter temperatures are coldest. On occasion, a tortoise will take cover
under a bush or any natural shelter. The burrows are often crucial to survival, especially in
hot weather when the direct rays of the sun can kill a tortoise in an hour or less (Marlow
1979). Reproduction
Copulation begins shortly after the tortoises become active in late March or
early April. Eggs are laid in early summer (late May to July). Clutches average 5 (range 2-9)
eggs and take 3-4 months to hatch (Miller 1932, Woodbury and Hardy 1948, Stebbins 1954).
Nests are often constructed at the entrance to burrows. Failure of rainfall and consequent
scarcity of annual plants may result in reproductive failure. Daily/Seasonal Activity
Tortoises may be active at any time of year, but most activity takes
place between March and June, and to a lesser extent in late summer in areas with summer
rains (eastern Mojave). In early spring, tortoises may be active all day but by late spring,
activity is reduced to less than an hour in early morning, 1 out of 4 days (Marlow 1979).
In Utah, tortoises migrate from winter dens to summer
feeding areas but this is not known to happen in California (Woodbury and Hardy 1948). Diet and Foraging
Tortoises are herbivorous, eating annual forbs and grasses; many species are
taken, but forbs are preferred over grasses and green vegetation is preferred over dry.
Desert tortoises have been observed eating carrion and feces as well as excavating and
eating calcium carbonate mineral deposits (Marlow 1979, Marlow and Tollestrup 1982). Territoriality/Home Range
Home range size seems to depend upon the quality of the habitat. In the
western Mojave, home ranges are 2-15 ha (5-38 ac), but in the eastern Mojave, home ranges
may be 10 times as large.
Tortoises are aggressive but there is no evidence that they defend territories. Predator-Prey Relations
When tortoises are young and vulnerable, they are eaten by many predators
(eagles, coyotes, foxes, etc.). When mature, they have few enemies (very hungry coyotes
may attack an adult tortoise). Captive tortoises are subject to respiratory infections but this
has not been observed in wild populations. Nothing is known about serious parasite
problems. Rabbits and a few rodents may compete with tortoises for food but this has not
been established (Marlow 1979). Literature Cited
Auffenberg, W., and R. Franz. 1978. Gopherus agassizii. Cat. Amer. Amphibians and
Reptiles 212.
Bramble, D. 1982. Scaptochelys: generic revision and evolution of gopher tortoises.
Copeia 1982:852-867.
Marlow, R. W. 1979. Energy relations in the desert tortoise, Gopherus agassizii. Ph.D.
Thesis, Univ. California, Berkeley. 155pp.
Marlow, R. W., and K. Tollestrup. 1982. Mining and exploitation of natural mineral
deposits by the desert tortoise, Gopherus agassizii. Anim. Behav. 30:457-478.
Miller, L. H. 1932. Notes on the desert tortoise (Testudo agassizii). Trans. San Diego
Soc. Nat. Hist. 7:187-208.
Stebbins, R. C. 1954. Amphibians and reptiles of western North America. McGraw-Hill,
New York. 536pp.
Woodbury, A. M., and R. Hardy. 1948. Studies of the desert tortoise, Gopherus agassizii.
Ecol. Monogr. 18:145-200.
Information gathered from California DFG - California Interagency Wildlife Task Group
