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

We monitored desert tortoise reproduction by radiography in 1998, for the second consecutive year, at Sugarloaf Mountain, Maricopa County, Arizona. We radiographed 22 telemetered tortoises bi-weekly from 21 May to 14 August. We also radiographed tortoises on 1 April, 1 May, 3 September and 6 October. Twelve of 18 tortoises > 220 mm MCL (66.7%) laid eggs, with clutch sized ranging from four to seven eggs ( = 5.42). These data do not include one tortoise found with a single egg from 30 April to 5 June. This egg was probably retained from the previous year, but we had not captured it until after the reproductive season and our radiographic survey in 1997. None of the 4 telemetered tortoises < 220 mm MCL (the smallest size documented to reproduce in the Sonoran Desert) had eggs. Oviposition occurred during the summer monsoon season, from mid July to early August. Above average winter-spring rainfall in 1997-98 may have contributed to higher reproductive output compared to 1997 (four of 12 females [33.3%] laying eggs, 3.25 eggs/clutch), which was preceded by below average summer and winter-spring rainfall. These results are more similar to 1993 (8 of 10 females [80%] laying eggs, 5.70 eggs/clutch) which was preceded by above average rainfall in both summer and winter-spring. We verified the exact location of several nests during 1997-98 and observed hatchling emergence from one nest in October 1998.