Desert tortoise (Gopherus agassizii) survival at two eastern Mojave Desert sites: Death by short-term drought?

Journal of Herpetology
By: , and 

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Abstract

Survival of adult Desert Tortoises (Gopherus agassizii) appears related to site-specific variation in precipitation and productivity of annual plants. We studied adult tortoise survival rates at two closely situated, but physiographically different, sites in the eastern Mojave Desert over a nine-year period (spring 1992 to spring 2001). Survival rates were initially derived from population surveys conducted over a three-year period and by radio-telemetry monitoring over a seven-year period beginning in 1994. After a period of initial stability, survival rates on the two sites diverged over the study period, and seven-year survival rates estimated from radio-telemetry monitoring were 0.900 and 0.269, respectively. A die-off in 1996 on the latter site appears to have been triggered by a period of drought, which began in the summer of 1995, coupled with a failure of annual vegetation production in 1996. Depressed survival rates on this site were associated with drought conditions during three of four years. Although the decline had the appearance of an epizootic, there were no clinical signs of disease. Relatively short-term drought, combined with little or no annual biomass, appears to have caused severe reductions in tortoise survival. If periods of drought-induced low survival are common over relatively small areas, then source-sink population dynamics may be an important factor determining tortoise population densities.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Desert tortoise (Gopherus agassizii) survival at two eastern Mojave Desert sites: Death by short-term drought?
Series title Journal of Herpetology
DOI 10.1670/0022-1511(2003)037[0169:DTGASA]2.0.CO;2
Volume 37
Issue 1
Year Published 2003
Language English
Publisher The Society for the Study of Amphibians and Reptiles
Contributing office(s) Western Ecological Research Center
Description 9 p.
First page 169
Last page 177
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