Archives of The Cold Blooded News

The Newsletter of the Colorado Herpetological Society

Volume 30, Number 6;   June, 2003

Natural History Notes

Range and Habitats of the Desert Tortoise

In the northern third of its range -- in the Mojave Desert -- the desert tortoise occurs in creosote bush scrub and Joshua tree woodlands. Tortoises here dig burrows in soft loamy sand in the broad desert valleys or in the gently sloping bajadas coming off the mountains. Rainfall is light, occurring mainly in the winter and spring, with summers being hot and dry. Peak tortoise activity takes place in the spring and again in the fall, followed by a long winter hibernation.

In the central portion of their range -- in the Sonoran Desert of Arizona -- tortoises are no longer found in the valley flats, but instead are found almost exclusively in steep rocky hillsides. Tortoises use rock shelters and small caves instead of long soil burrows. Rainfall is higher, with a significant portion falling in summer. Because of the rainfall, peak tortoise activity is in summer.

Tortoises in the southern portion of their range -- the Sinaloan population -- occupy a region of tropical deciduous forests with dark, wet floors. Rainfall is considerably higher and occurs chiefly in the summer, with a pronounced spring drought. It is believed that tortoises remain active during the mild winter, but may estivate during the spring dry season.

Of the three populations, the Mojave is by far the most well studied; comparatively little is known about the Sinaloan tortoises. Recently, data has revealed significant genetic and ecological differences among these three populations. Further studies are needed, however, to determine if these differences are great enough to warrant separate species status for the populations.