29th Annual Meeting and Symposium of the
Desert Tortoise Council, February 20-23, 2004
Abstracts

Drought: Acute Effects and Impacts to Recovery of the Desert Tortoise

Alice E. Karl
P.O. Box 74006, Davis, CA 95617

The Mojave desert has experienced an unusually severe drought cycle in the past 15 years. In the west Mojave, 7 of the past 15 years have been spring droughts with negligible or well below-average forage production. In the east Mojave, spring droughts have occurred in 8 of the past 15 years. Desert tortoise populations have declined dramatically during this period. Declines that have been documented for specific year groups are overwhelmingly associated with drought years. Drought has contributed both proximately and ultimately to these declines. Proximately, dehydration and starvation result in elevated mortality. Ultimately, drought likely contributes to other factors that are directly responsible for tortoise mortality, such as mycoplasmosis and increased depredation.

While the desert tortoise is adapted to seasonally dry conditions and periodic annual drought, frequent drought years within a relatively short period result in high mortality rates, reduced reproduction, reduced individual growth (leading to delayed reproduction), and reduced recruitment. These factors are discussed relative to population recovery.