Book excerpt: 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.