26th Annual Meeting and Symposium of the
Desert Tortoise Council, March 16-18, 2001
Abstracts

Sonoran Desert Tortoise Population Monitoring, 1987-2000

Roy C. Averill-Murray¹ and Peter Woodman^2
1Arizona Game and Fish Department, 2221 W Greenway Road, Phoenix, AZ 85023
²Kiva Biological Consulting, P.O. Box 1210, 8626 Las Flores, Inyokern, CA 93527

To date, 17 Sonoran desert tortoise population plots have been surveyed under funding from the Arizona Game and Fish Department, Bureau of Land Management, and Fish and Wildlife Service (several others have been surveyed by other agencies). Tortoise densities within local populations vary widely, ranging from 15 to more than 100 adults per square mile, and density is apparently related to habitat features providing burrow sites. Sex ratios are typically balanced between males and females. Symptoms of upper respiratory tract disease have occasionally been observed on plots, and cutaneous dyskeratosis is present in virtually all populations. However, disease has not impacted Sonoran populations as it recently has in the Mojave Desert. Notable human-related impacts to some populations include predation by feral dogs, burrows trampled by cattle, tortoises trapped in a mining pit, adjacent development, and shot and vandalized tortoises (or a released pet). Only one documented population crash has occurred in the Sonoran Desert in Arizona during the last 13 years, and it appears to have been related to drought rather than disease, although substantial numbers of carcasses have been found at a few other sites. Other populations appear to be stable, based on the current data.