The Desert Tortoise (Gopherus agassizii) is one of four species of land tortoises found in the United States and Mexico, primarily in Eastern California, Arizona, and Northern Mexico.
The two notable populations of desert tortoise in the United States are the Mojave and the Sonoran desert tortoises. The two populations have been classified as separate subspecies, possibly due to their genetic separation by a flow of the Colorado River some 5 million years ago. Populations of Mojave desert tortoises found north and west of the Colorado River have been listed as threatened since August of 1980. Sonoran desert tortoises found in Arizona have been listed as candidate species since December of 2010.
Desert tortoises can weigh up to 15 pounds, and reach a shell length of 15 inches. Desert tortoises are also dimorphic, with males being larger than females.
In the Mojave populations, desert tortoises inhabit canyon bottoms, alluvial fans, and soils suitable for burrowing up to elevations of 4000 feet. Tortoises also frequently burrow under creosote bushes for the cooling effect that humidity from root structures provide.
Desert tortoises spend large portions of the year underground in burrows to protect themselves from heat, cold, and predation. Time spent outside of burrows is primarily in the spring and fall, and after significant rainfall, to support feeding and reproductive activities.
Burrows can be dug horizontally some 8 to 30 feet, and as deep as 3-4 feet. Burrow construction is a critical component in the current debate over hunter access in desert tortoise habitat. Some researchers have alleged that tortoise mortality occurs when hunters or their vehicles collapse tortoise burrows. Given the significant lack of evidence demonstrating that hunters and their vehicles are specifically responsible for tortoise mortality in this manner, this issue remains controversial in its effect in limiting hunter access. Additional controversy exists related to cattle collapsing tortoise burrows, as well as the effects of grazing on food supplies favored by tortoises in certain times of the year.
Primary causes of desert tortoise mortality include Upper Respiratory Tract Disease , predation by coyotes, feral dogs, ravens, foxes, golden eagles, egg predation by ravens and skunks, exposure to environmental toxins in soil, mortalities related to vehicles on pavement being crossed by tortoises, and until recently mortality related to euthanasia by Desert Tortoise Recovery Program personnel.
Research of public records by Hunt for Truth indicate that claims of hunters and shooters causing tortoise mortality by “vandalism” (shooting) are based upon a limited and potentially flawed forensic analysis of shell fragments by Dr. Kristin Berry in 1984. Hunt for Truth has contracted with Dr. Frederic Tulleners to re-analyze Dr. Berry’s questionable claims of shooting mortality, given that Dr. Tulleners was the analyst first approached by Dr. Berry for her work. Hunt for Truth is continuing its research in debunking unsubstantiated claims that hunters and shooters are responsible for additional tortoise mortalities in violation of state and Federal law.
