Twenty-Fourth Annual Meeting and Symposium of the Desert Tortoise Council, March 5-8, 1999
Abstracts

In late May 1998, we began the first field season of a two year investigation into the reproductive ecology of a wild population of desert tortoises at the Marine Corps Air Ground Combat Center, 29 Palms, California. We monitored the reproductive status of 19 adult female tortoises using radiographic analysis. Two females did not produce eggs, 15 produced one clutch and two produced two clutches. Mean clutch size was 5.2 eggs (n=17) and ranged from 3-9 eggs. Using thread trailing devices attached to the carapace of gravid females, we located 17 of the 19 nests laid. Two nests were laid under creosote bushes, one was within a pallet and 15 were associated with burrows. Eight of seventeen nests (47%) were depredated. Kit foxes were implicated by circumstantial evidence in most predation events. Seventy-seven percent of the eggs in surviving nests emerged successfully from the nest chamber. Incubation time ranged between 74 and 88 days, though one abnormally pigmented individual emerged after 106 days. Hatchlings were measured and a sub-sample was monitored with radiotransmitters for survivorship and movement patterns. Only one of 11 hatchling tortoises was predated prior to October 22nd, when all transmitters were removed. These data give a preliminary look at the nest site selection of gravid females and survivorship of nests, eggs and hatchling desert tortoises in a robust Mojave Desert population.