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

The Tortoise and the Gila Monster: Common Place; Common Destiny?

Daniel D. Beck
Department of Biological Sciences, Central Washington University, Ellensburg, WA 98926

The desert tortoise shares much of its geographic distribution with its rival, the Gila monster. Gila monsters have been observed feeding on tortoise eggs and tortoises have been observed to vigorously defend their shelters and nests from marauding Gila monsters. However, these two ancient desert denizens share more than just habitat. Both are long-lived members of very old genera, dating back at least 23 million years. Both have evolved a frugal energy use strategy as a means to cope with the predictable food shortages that occur in their desert habitats. Both species exhibit impressive combat behaviors and both rely heavily on shelters to provide suitable microenvironments, refuge from predators, and access to favorable thermoregulatory sites, foraging areas, and potential mates. In contrast to the desert tortoise, the Gila monster remains an elusive and poorly understood icon of the American Southwest. While the Gila monster is not federally listed, populations of Heloderma suspectum cinctum throughout the Mojave Desert are listed by individual states as "endangered", "imperiled", or "extremely imperiled". Most desert habitats support Gila monster population densities far below those of the desert tortoise, yet resource managers still do not have sufficient information on the distribution, population characteristics, or habitat needs of Gila monsters to make informed management decisions. Gila monsters were once very common around St. George, Utah, but the explosive growth of Washington County has eliminated much of the lizard's historic habitat in that state. Ironically, a promising new drug for treating adult onset diabetes (which afflicts 17 million Americans) has recently been discovered from Gila monster venom samples originating in Utah. Washington County's Habitat Conservation Plan, prepared in response to federal listing of the Desert tortoise, offers the best chance for survival of remaining Utah Gila monster populations. The desert tortoise, therefore, may act as an umbrella species for Heloderma suspectum, and thereby protect vital habitat for Gila monsters. This will happen only if biologists and resource managers take a more proactive approach to understanding the distribution, habitat needs, and ecology of the Gila monster. Otherwise, we could see the difficult history of the desert tortoise in the Mojave Desert repeated by America's largest, and only venomous, lizard.