Fact Sheet
Desert Tortoise

Threats to Desert Tortoises

Human Disturbance

Because it is so well adapted to and dependent on its habitat for survival, the desert tortoise is very sensitive to any changes in it. As a result, certain human activities have caused significant changes in the nature and condition of desert tortoise habitat in the Mojave Desert region.  These changes have resulted in the elimination or steep declines of many desert tortoise populations, such as in the Western Mojave Desert in California where overall declines now approach 90 percent over just the past 40 years.  Such losses are common near cities and urban developments, agricultural and industrial developments such as in the Las Vegas valley of Nevada, and the Antelope, Victor and Indian Wells Valleys in California.  In more remote areas of the Mojave, development of highways, roads, railroads, canals, pipelines and electricity transmission systems have resulted in fragmentation of otherwise high-quality habitat, leading to isolated populations of desert tortoises and increased mortality from vehicle use and entrapment.  Poaching, livestock grazing, excessive use of off-highway vehicles within tortoise habitat and crushing by automobiles continue to threaten tortoise populations.

Climate Change

Climate change projections indicate that difficult times lay ahead for the desert tortoise as increased temperatures and decreased precipitation and soil moisture expand over the region. Like all reptiles, tortoises have minimal ability to self-regulate their internal temperature, and thus must retreat to the shade of vegetation or their burrows once the air temperature climbs above about 90 degrees Fahrenheit, in order to keep their body temperatures out of the danger zone. Drought also decreases the amount of wildflowers and grasses available to desert tortoises, which is their primary food supply during the spring and fall seasons.  During drought, tortoises spend more time in their underground burrows to minimize water loss and conserve energy.

Females tortoises also lay fewer eggs, or none at all, during severe drought years. Furthermore, the sex of tortoises is determined by the soil temperature where adult females lay their eggs. Temperatures above 88.7 degrees Fahrenheit during egg incubation favor development of female tortoises, so prolonged high temperatures could skew the sex distribution of future generations. Extremely high soil temperatures (above 95 degrees) are lethal to the developing young.

Predation

Raven and coyote predation causes significant losses of tortoises in many areas of the Mojave Desert where these naturally occurring predators have increased in numbers, especially near cities, towns, campgrounds and day-use recreational facilities.  During times of drought, ravens and coyotes turn to desert tortoises as one of their primary sources of food.  Ravens are especially adept in preying on hatchling and other small-sized desert tortoises.

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Conservation Issue
While all wildlife has inherent value, some species serve a vital role in their ecosystem, enabling countless other species to survive and thrive. Plants, animals and insects like these are called “focal species,” of which there are five types. Each designation carries a different distinction for how these species interact with and affect their environments. · Foundational species: serve a pivotal role in their ecosystem by providing some ecosystem service upon which other species depend. Bees are foundational to ecosystems across the country, pollinating wild and cultivated plants that are essential to both wildlife and human economies worth billions of dollars. · Indicator species: are very sensitive to environmental changes in their ecosystem. An indicator species is affected almost immediately by damage to the ecosystem and can provide early warning of that a habitat is suffering. Freshwater mussels are well-known indicators of water quality conditions in rivers and lakes. A sudden increase in mortality of freshwater mussels is a reliable indicator of toxic contamination and the steady disappearance of mussels over time can be indicative of chronic water pollution. Moreover, biologists can measure the amount of pollutants found in mussel shells and tissue to determine the type, extent, and even timing of water pollution events in streams and lakes. · Keystone species: have a disproportionately large effect on the communities in which they occur. Such species help to maintain local biodiversity within a community either by controlling populations of other species that would otherwise dominate the community or by providing critical resources for a wide range of species. The wolf is a famous example of a keystone species. By controlling the numbers of grazing animals on a landscape, wolves help plant life thrive, which has the further positive affect on many other species, from birds to beavers and fish. The return of wolves to Yellowstone National Park has literally transformed that landscape. Vegetation restored from decades of overgrazing by elk even changed the path of the Yellowstone River. · Umbrella species: are a species whose conservation is expected to confer protection to a large number of naturally co-occurring species. They are similar to keystone species, but are usually migratory and need a large habitat. A good example of an umbrella species is sage grouse. They need large expanses of healthy sagebrush grasslands and functioning hydrologic systems to survive and flourish. Conserving sage-grouse benefits a host of other species in the Sagebrush Sea including, pronghorn, elk, mule deer, native trout, and nearly 200 migratory and resident bird species. The success or decline of a focal species tells us something important about the health of their ecosystem. By closely monitoring these species, we can see the early warning signs of trouble within an ecosystem, and begin to investigate potential problems. Conserving and restoring these native species to their respective landscapes makes for healthier, more natural, more resilient ecosystems where wildlife of all kinds can thrive. Many of these influential species have declined over the last century for a variety of reasons. Conserving and restoring these native species to their respective landscapes makes for healthier, more natural, more resilient ecosystems where wildlife of all kinds can thrive.
Where We Work
Our Southwest team works to protect rare and threatened species like Mexican wolves, jaguars and ocelots.
Where We Work
The Golden state is home to millions of wild birds, mammals, amphibians, reptiles and fish that need our help.