27th Annual Meeting and Symposium of the
Desert Tortoise Council, March 22-24, 2002
Abstracts

STUDENT PAPER

Nesting Success of Desert Tortoises (Gopherus agassizii) at Ivanpah Valley, CA and Fort Irwin Reference Site, CA During the Year 2000

Bryan R. Franks
School of Environmental Science, Engineering, and Policy, Drexel University, Philadelphia, PA 19104

Between May and July 2000, twenty-four adult female desert tortoises were monitored for egg laying, 7 from the Fort Irwin Reference Site, CA (FIRS) and 17 from Ivanpah Valley, CA. FIRS is located just outside the southeastern edge of the National Training Center at Fort Irwin, CA. Ivanpah Valley is located within the Mojave National Preserve. Ten nests were found, 6 from Ivanpah Valley and 4 from FIRS. All 10 nests were laid inside burrows that were dug under creosote bushes. The average clutch size for nests found at FIRS was 3.5 eggs while the average clutch size for nests in Ivanpah Valley was 5.7 eggs. Nine of 10 nests were destroyed either by predation or flooding. Seven of the 10 were confirmed as predated. A coyote was assumed to be the predator for one of the nests while kit foxes were suspected as predators in the other 6 predated nests. In Ivanpah Valley, flooding was assumed to be the reason for mortality in two of the nests. One nest was monitored for 85 days and hatching did not occur. It was assumed that these eggs died due to collapse of the burrow and heavy rainfall in late August. Therefore, there was 100% mortality for the nests found with 0% hatching success and a predation rate of 70%. These results for hatching success, nest mortality, and predation rate shows that head starting of desert tortoise nests and hatchlings in predator proof enclosures may be a valuable tool in recovering desert tortoise populations.