The Mojave desert tortoise is a large, herbivorous (plant-eating) reptile that occurs in the Mojave Desert north and west of the Colorado River in southwestern Utah, southern Nevada, southeastern California, and northwestern Arizona in the United States. The desert tortoise is one of most elusive inhabitants of the desert, spending up to 95% of its life underground. The desert tortoise lives in a variety of habitats from sandy flats to rocky foothills, including alluvial fans, washes and canyons where suitable soils for den construction might be found. Tortoises have lived in the area that is now the Mojave Desert for millions of years, even before it was a desert. As recently as the mid-1900s, people commonly encountered these familiar, gentle creatures. Today, they are rarely seen and in some places they have disappeared entirely. The Mojave desert tortoise was listed as Threatened on April 2, 1990, and was originally listed as the Mojave population of the desert tortoise. However, recent studies have concluded that the Mojave desert tortoise and Sonoran desert tortoise are distinct species.
The vast majority of threats to the desert tortoise or its habitat are associated with human land uses. The most apparent threats to the desert tortoise are those that result in mortality and permanent habitat loss across large areas, such as urbanization and large-scale renewable energy projects, and those that fragment and degrade habitats, such as proliferation of roads and highways, off-highway vehicle activity, habitat invasion by non-native invasive plant species, wildfire, and subsidized predators (especially common ravens). These threats interact in complex and synergistic ways to impact tortoise populations.
The desert tortoise requires 13 to 20 years to reach sexual maturity, has low reproductive rates during a long period of reproductive potential, and individuals experience relatively high mortality early in life. These factors make recovery of the species difficult. Even moderate downward fluctuations in adult survival rates can result in rapid population declines. Thus, high survivorship of adult desert tortoises is critical to the species’ persistence, and the slow growth rate of populations can leave them susceptible to extirpation events in areas where adult survivorship has been reduced. Another factor integral to desert tortoise recovery is maintaining the genetic variability of the species and sufficient ecological heterogeneity within and among populations to allow tortoises to adapt to changes in the environment over time. Because desert tortoises occupy large home ranges, the long-term persistence of extensive, unfragmented habitats is essential for the survival of the species. The loss or degradation of these habitats to urbanization, habitat conversion from frequent wildfire, or other landscape modifying activities place the desert tortoise at increased risk of extirpation.
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