Reptiles
Desert Tortoise
Gopherus agassizii · also called Mojave desert tortoise, Agassiz's desert tortoise
The desert tortoise makes a living in one of the hottest, driest places in North America by hardly ever being above ground and by carrying its water with it. It spends most of the year in a burrow, and it stores nearly a year’s supply of water in its own bladder.
Overview
Gopherus agassizii, the Mojave desert tortoise, lives on the desert flats and washes of southeastern California, southern Nevada, southwestern Utah, and northwestern Arizona. It eats spring wildflowers, grasses, and cactus and gets most of its water from that food.
Water in the bank
It stores a large volume of dilute urine in its bladder and reabsorbs water from it over months. A frightened tortoise often empties its bladder, so handling a wild one in the dry season can kill it. Some dig shallow rain-catching basins they return to after storms.
A keystone burrower
It spends up to 95 percent of its life underground, in burrows that also shelter more than 350 other species, from burrowing owls to kit foxes and rattlesnakes.
Status
Critically Endangered internationally and federally Threatened, with Mojave populations down roughly 90 percent since the 1980s from development, roads, disease, and raven predation on hatchlings. It matures at 15 to 20 years, so recovery is measured in decades.
Desert Tortoise: common questions
Why should you never pick up a wild desert tortoise?
Because it may cost the animal its life. A desert tortoise carries much of its water supply as dilute urine stored in its bladder, and it can reabsorb that water slowly over the many months between desert rains. When a tortoise is startled, chased, or lifted, its common response is to empty its bladder in one go. In the wet season that is a minor loss, but in a dry stretch, which is most of the year, a tortoise that has just dumped its water reserve and cannot find a puddle to replace it can die of dehydration. So the rule in tortoise country is to watch one from a distance and never handle it, except to move a tortoise that is directly in the path of a car, gently, a short way, in the direction it was heading.
How does the desert tortoise get enough water in the Mojave?
Mostly from its food and its own storage system. In spring, when rain has triggered a flush of desert annuals, the tortoise eats heavily on moisture-rich wildflowers and new growth, taking in far more water than it needs at that moment and banking the surplus. It stores water in its bladder, holds nutrients as fat, and then draws on both through the long dry summer and the cold winter spent underground. When a summer thunderstorm does fall, tortoises come out to drink deeply from puddles and from shallow rain-catching basins some of them have dug, topping up the reservoir before retreating.
Why are desert tortoises disappearing?
Many pressures at once, acting on an animal that breeds very slowly. Large areas of Mojave habitat have been lost to housing, roads, military ranges, and utility-scale solar farms, and remaining habitat is fragmented and criss-crossed by roads where tortoises are crushed. Ravens, whose numbers have exploded thanks to human food, rubbish, and perches, kill huge numbers of soft-shelled hatchlings. An upper-respiratory disease, spread in part by released or escaped pet tortoises, sickens wild populations. Off-road vehicles collapse burrows and compact soil. Because a female does not breed until she is 15 to 20 and then lays only a few eggs, the population cannot make up these losses, and numbers across the Mojave have fallen by around 90 percent in a few decades.
Can you keep a desert tortoise as a pet?
In parts of the southwestern United States, captive desert tortoises that are already in the pet population, and their offspring, can be kept legally under a permit or adoption programme, and there are more captive tortoises than wild ones in some states. But it is illegal to take a tortoise from the wild, and captive tortoises must never be released, because they can carry the respiratory disease that is devastating wild populations, and a released animal may also disrupt local genetics. Anyone who can no longer care for a pet desert tortoise should surrender it to an official adoption programme rather than letting it go.