28th Annual Meeting and Symposium of the
Desert Tortoise Council, February 21-23, 2003
Abstracts

Incidence of Disease Symptoms at Sonoran Desert Long-term Monitoring Plots

J. Daren Riedle* and Roy C. Averill-Murray
Arizona Game and Fish Department 2221 W. Greenway Rd. Phoenix, AZ 85023

The systematic study of long-term monitoring plots in the Sonoran Desert began in 1987. Fifteen plots had been established by 1993. The Arizona Game and Fish Department, through private contractors, surveys up to 5 plots per year, and all plots have been surveyed at least twice, and some have been surveyed 6 or more times. Tortoise density at survey plots varied from 15 to over 100 tortoises per square mile. All tortoises captured during plot coverages were observed for signs of upper respiratory tract disease (URTD) and cutaneous dyskeratosis. Through 2000, less than 20% (usually less than 10%) of tortoises found on annual plot surveys showed visible symptoms of URTD, and many of the documented symptoms are uncertain. In 2002, results from ELISA tests on 41 tortoises from 6 plots tested negative for Mycoplasma. Cutaneous dyskeratosis was present in 0-70% of tortoises on the plots. There have been a few localized die-offs, although causes for the population crashes are unknown. Current questions center on whether it is a combination of factors such as drought and disease or possibly natural population cycles. Tortoises in the Sonoran desert live in relatively small, isolated populations that may be subject to periodic fluctuations. Little is known about the biology of Sonoran tortoise populations as current research has taken place over less than one tortoise generation. Continuation of long-term monitoring, in addition to other natural history studies, will continue through the future and hopefully begin to answer some of these questions.