Twenty-Third Annual Meeting and Symposium of the
Desert Tortoise Council, April 3-5, 1998
Abstracts

Three study sites were established in California in the spring of 1997 as part of a multi-year study to examine variation in reproductive output of desert tortoises: Joshua Tree National Park (JTREE), Mojave National Preserve (MOJAVE), and an area of land leased by the Bureau of Land Management (BLM) for wind energy production near Palm Springs (MESA). At MESA, 9 out of 10 monitored females produced a total of 72 eggs. Of these females, 6 produced second clutches and one produced a third clutch. Clutch size ranged from 2-8 eggs. Modal clutch size was 4 eggs. Mean clutch sizes were 4.33 and 5.00 eggs for first and second clutches, respectively. First clutch size was positively correlated with carapace length (r²=0.29) but not significantly (P=0.14). When all clutches were considered, a significantly positive relationship was detected (r²=0.26, P=0.04) The earliest date of egg laying occurred between April 18-23. The last clutch was oviposited sometime after July 3. At JTREE, only 1 of 8 females produced a single clutch (5 eggs). At MOJAVE, 12 of 18 monitored tortoises produced 43 eggs in 12 single clutches with no subsequent clutches. Clutch size ranged from 1-7 eggs with modal clutch size of 3-4 eggs. Mean clutch size was 3.58 eggs. Larger females produced larger clutches and the relationship between the two variables was almost significant (r²=0.32, P=0.055). Most of the variation observed appears to be related to differences among sites in rainfall and associated production of annual food plants.