Biological diversity is threatened by increasing anthropogenic modification of natural environments and increasing demands on natural resources. Sonoran desert tortoises (Gopherus morafkai) currently have Candidate status under the Endangered Species Act (ESA) based on health and habitat threats. To ensure this animal persists in the midst of multiple threats requires an understanding of the life history and ecology of each population. I looked at one physiological and one behavioral aspect of a population of tortoises at the Sugarloaf Mountain (SL) study site in central Arizona, USA. I used 21 years of capture-recapture records to estimate growth parameters of the entire population. I investigated habitat selection of juvenile tortoises by selecting 117 locations of 11 tortoises that had been tracked by radio-telemetry one to three times weekly for two years, selecting locations from both summer active season and during winter hibernation. I compared 22 microhabitat variables of tortoise locations to random SL locations to determine habitat use and availability. Male tortoises at SL reach a greater asymptotic length than females, and males and females appear to grow at the same rate. Juvenile tortoises at the SL site use steep rocky hillsides with high proportions of sand and annual vegetation, few succulents, and enclosed shelters in summer. They use enclosed shelters on steep slopes for winter hibernation. An understanding of these features can allow managers to quantify Sonoran desert tortoise habitat needs and life history characteristics and to understand the impact of land use policies.

One of the most recognizable animals of the Southwest, the desert tortoise (Gopherus agassizii) makes its home in both the Sonoran and Mohave Deserts, as well as in tropical areas to the south in Mexico. Called by Tohono O'odham people "komik'c-ed," or "shell with living thing inside," it is one of the few desert creatures kept as a domestic pet—as well as one of the most studied reptiles in the world. Most of our knowledge of desert tortoises comes from studies of Mohave Desert populations in California and Nevada. However, the ecology, physiology, and behavior of these northern populations are quite different from those of their southern, Sonoran Desert, and tropical cousins, which have been studied much less. Differences in climate and habitat have shaped the evolution of three races of desert tortoises as they have adapted to changes in heat, rainfall, and sources of food and shelter as the deserts developed in the last ten million years. This book presents the first comprehensive summary of the natural history, biology, and conservation of the Sonoran and Sinaloan desert tortoises, reviewing the current state of knowledge of these creatures with appropriate comparisons to Mohave tortoises. It condenses a vast amount of information on population ecology, activity, and behavior based on decades of studying tortoise populations in Arizona and Sonora, Mexico, and also includes important material on the care and protection of tortoises. Thirty-two contributors address such topics as tortoise fossil records, DNA analysis, and the mystery of secretive hatchlings and juveniles. Tortoise health is discussed in chapters on the care of captives, and original data are presented on the diets of wild and captive tortoises, the nutrient content of plant foods, and blood parameters of healthy tortoises. Coverage of conservation issues includes husbandry methods for captive tortoises, an overview of protective measures, and an evaluation of threats to tortoises from introduced grass and wildfires. A final chapter on cultural knowledge presents stories and songs from indigenous peoples and explores their understanding of tortoises. As the only comprehensive book on the desert tortoise, this volume gathers a vast amount of information for scientists, veterinarians, and resource managers while also remaining useful to general readers who keep desert tortoises as backyard pets. It will stand as an enduring reference on this endearing creature for years to come.

During a long-term study on tortoise growth within 3 fenced 9-ha enclosures in Rock Valley, Nevada Test Site (NTS), Nye County, Nevada, USA, tortoises have been captured annually since 1964 (Medica et al. 1975. Copeia 1975:630-643; Turner et al. 1987. Copeia 1987:974-979). Between early August and mid October 2003 we observed a significant mortality event. The Rock Valley enclosures were constructed of 6 x 6 mm mesh 1.2 m wide hardware cloth, buried 0.3 m in the soil with deflective flashing on both sides on the top to restrict the movement of small mammals and lizards from entering or leaving the enclosures (Rundel and Gibson 1996, Ecological communities and process in a Mojave Desert ecosystem: Rock Valley, Nevada, Cambridge University Press, Great Britain. 369 pp.). On August 6, 2003, the carcass of an adult female Desert Tortoise No. 1411 (carapace length 234 mm when alive) was collected while adult male tortoise No. 4414 (carapace length 269 mm) was observed alive and in good health on the same day. Subsequently the carcass of No. 4414 was found on October 16, 2003. Between October 16-17, 2003, the remains of 6 (5 adult and 1 juvenile) Desert Tortoises were found, some within each of the 3 enclosures in Rock Valley. A seventh adult tortoise was found on September 26, 2006, its death also attributed to the 2003 mortality event based upon the forensic evidence. Each of the 7 adult Desert Tortoises had the central portion of their carapace broken open approximately to the dorsal portion of the marginal scutes while the plastron was still intact (Figure 1A). Adjacent to 7 of the 8 remains we located numerous bone fragments including parts of the carapace and limbs as well as dried intestines in a nearby Range Rhatany (Krameria parvifolia) shrub. The significance of the frequent use of this shrub is puzzling. Three of the Desert Tortoise shell remains possessed distinctive intercanine punctures measuring 55-60 mm center to center indicating that this was an adult sized Mountain Lion. By comparison, a 2 year old male Mountain Lion salvaged on NTS had an upper intercanine bite width of 45 mm, and a 6 month old kitten measured 35mm respectively. The Mountain Lion (Puma concolor) is the only predator that exists in southern Nevada that could possibly have a bite with a gap between its upper canine teeth that large (Murmann et al. 2006. J. Forensic Sci. 51:846-860). The appearance of the shell remains in Figure 1A is similar to that depicting Jaguar (Panthera onca) predation, on the Amazonian Tortoise (Geochelone denticulata) as illustrated by Emmons (1989. J. Herpetol. 23:311-314) with the majority of the carapace broken open and the plastron still intact. Predation of Desert Tortoises by Mountain Lions was also documented in 1993 in southern Arizona (Little Shipp Wash Plot), where 7 of 8 carcasses found were attributed to Mountain Lion predation (Averill-Murray et al. 2002. In. T.R. Van Devender [ed.], The Sonoran Desert Tortoise: Natural History, Biology, and Conservation, pp. 109-134. University of Arizona Press and Arizona-Sonora Desert Museum, Tucson, Arizona). Similarly, predation by a Mountain Lion has been reported on the Argentine Tortoise (Chelonoidis chilensis) in Argentina (Acosta et al. 2004. Herpetol. Review 35:53-54), and a Mountain Lion kitten was observed to kill and consume a portion of the carapace of a Texas Tortoise (Gopherus berlandieri) in west Texas (Adams et al. 2006. Southwestern Nat. 51:581-581). Over the past 45 years this Desert Tortoise population has been monitored yearly, with no prior evidence of predation to tortoises within the fenced enclosures. On several occasions other predators such as Bobcats (Lynx rufus) have been observed within the study enclosures for as long as a week. Evidence of Kit Fox (Vulpes macrotus) sign has been observed on numerous occasions, and a Spotted Skunk (Spilogale putorius) and Longtail Weasels (Mustela frenata) have been captured and released (B.G. Maza, pers. comm.; Medica 1990. Great Basin Nat. 50:83-84), while Coyotes (Canis latrans) were never observed within the fenced enclosures. Prior to this predation event in Rock Valley, 17 Desert Tortoises were alive between 2000 and 2002, only 7 were known to be alive in 2004, while 2 tortoises have not been seen since 2002. Predation studies of Mountain Lions indicate that these events may be an example of a learned behavior of individual animals developing a preference for a prey (Logan and Sweanor 2001, Desert Puma: Evolutionary ecology and conservation of an enduring carnivore. Hornocker Wildlife Institute, Island Press, Washington. 463 pp.; Creeden and Graham 1997, Desert Bighorn Council Transactions. p. 37-43), or the plight of a large predator locating an available source of food while passing through low elevation Mojave Desert habitat in late summer or early fall.

Provides an overview of extant desert tortoise literature, summarizing literature on taxonomy, morphology, genetics, and paleontology and paleoecology of the desert tortoise, as well as its general ecology. Literature on desert tortoise ecology encompasses distribution and habitat, burrows and dens, reproduction, growth, physiology, feeding and nutrition, mortality factors, and behavior. Information on habitat deterioration, management of tortoises, their legal status and tortoise husbandry is also included. The manuscript is a complete overview of existing literature, including peer-reviewed literature and other literature. Information was compiled from materials available in 1991.