Tortoise Island

May 2007

If you see a rock move on its own in the desert, look again. That rock may be a tortoise. In the Deem Hills, desert tortoises have been sighted by at least three neighbors I’ve talked with. Two of the tortoises were quite large animals (12” long or so), resolutely lumbering across the trail above Hackberry Lane. Unfortunately, the third sighting was only a shell and a few bones, the rest of the tortoise having been a good-sized meal for some other desert animal. Were all three sightings of the same tortoise? Or are there more of these amazing animals surviving in the desert island of our big backyard?

In the Sonoran desert, tortoises are fairly common, preferring hilly, rocky territory where palo verde and saguaros grow, which fits the description of Deem Hills. Tortoises spend their lives in a narrow range of a few square miles and are mostly solitary. Their continued survival depends on males and females meeting one another occasionally, but only occasionally, as the females can retain sperm for up to two years and still produce several viable clutches of eggs. Once a female has mated, she may dig a small cavity to lay her eggs sometime between May and July. The eggs hatch about ninety days later, hopefully coincident with the summer rains so that the young tortoises have the best chance of survival.

Since tortoises spend over 90% of their lives resting in rocky dens, shallow burrows, or shady depressions under shrubs, seeing a live tortoise moving around in the wild is a very rare treat for anyone. A tortoise may live up to fifty years in the desert, although survival in the first five years is quite risky due to predation of eggs and young by ravens, coyotes, foxes, roadrunners and other animals. Desert tortoises are most active in late spring and early fall months, or in the cooler mornings and evenings during summer months. They are herbivores, feasting on over a hundred species of plants, including prickly pear cactus, wildflowers and grasses. Almost all of the moisture they need comes from the plants they eat, although they will drink whenever water is available.

Aside from predators, one of the greatest threats to a tortoise is curious people who pick them up and/or take them home for pets. Touching or picking them up may frighten them into releasing stored water, which then may be very difficult to replace, resulting in slow death from dehydration. Capturing, killing, or trading wild tortoises is illegal.

As I wander in the Deem Hills, one of my greatest wishes is that the female tortoise whose shell was left behind, also left dozens of extended family and offspring who are now safely sheltered in their burrows, feeding on prickly pear fruit, resting comfortably beneath a palo verde, and bumping into each other now and then to continue populating our tortoise island.
For more information on Sonoran desert tortoises, visit the Arizona Game and Fish Department web page on desert tortoise management at www.azgfd.gov/w_c/desert_tortoise.shtml.