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

Desert Tortoise Reproduction at Two Sites in the Sonoran Desert

Eric W. Stitt¹, Roy C. Averill-Murray², Terry E. Christopher³, Don E. Swann⁴, and Cecil R. Schwalbe^5
1Wildlife and Fisheries Science, University of Arizona, 125 Biological Sciences East, Tucson, AZ, 85721; 
²Arizona Game and Fish Department, 2221 West Greenway Road, Phoenix, AZ, 85023;
³Smithsonian Institution, Las Vegas, NV; 
⁴Saguaro National Park, 3693 South Spanish Trail, Tucson, AZ, 85730, and 
⁵U.S. Geological Survey, Sonoran Desert Field Station, Tucson, AZ, 8572

In 2001, we studied the reproductive effort for female desert tortoises at two sites in the Sonoran Desert. We monitored female tortoises from May to October by using ultrasound and x-radiography. At Sugarloaf, 60% (9 of 15) of mature (Midline Carapace Length >220 mm) females developed eggs. None of three individuals <220 mm (187-199 mm) produced eggs. Mean clutch size was 5.3 eggs (range, 4-9). At Saguaro National Park, we monitored 14 female tortoises. Of these, 71% developed egg clutches. Mean clutch size was 6.9 eggs (range, 1-9). At both sites, ovarian follicles were observed in early May, and all clutches were deposited by August 9. We monitored two nests throughout the incubation period. One failed to hatch; the other produced 7 neonates. All neonates were small (mean mass = 12.4 g, average MCL = 36.7 mm), and most failed to survive.