Archives of The Cold Blooded News

The Newsletter of the Colorado Herpetological Society

Volume 31, Number 8;   August, 2004

Desert Tortoises and Water

Desert tortoises live in some of the driest places on earth. Acquiring water is a challenge for tortoises as it is for all desert animals. Some desert animals such as kangaroo rats are famous for never needing to drink liquid water -- they get all the water they need metabolically from the seeds they eat. However, while desert tortoises can go months without liquid water, at some point they require it.

Most of the rain in the Mojave Desert falls during winter when tortoises are hibernating. Some rain occurs in spring and summer during brief rainstorms. This is when tortoises are able to replenish their water supply. Tortoises also get water from the fleshy, succulent annuals they consume in spring. During storms, water accumulates in depressions on the ground and on rock surfaces. These small pools are very ephemeral, quickly evaporating in the summer heat, so tortoises must act quickly to get a drink.

Tortoises also dig their own small drinking depressions. These small, saucer-shaped depressions several centimeters deep are dug in areas of desert pavement. Tortoises dig away the small pebbles on the surface of the pavement down to the silt layer. Because this silt layer is relatively impermeable, water stays on the surface until it is evaporated away. Tortoises know the locations of the drinking depressions within their home range, and will quickly gather there during rainstorms.

When tortoises drink, they submerge half their head and take deep gulps. They will do this for an extended period (10 minutes or more) and can increase their body weight by as much as 17 percent.

Tortoises use their bladders like a canteen, storing water there where it can be reabsorbed later. This water is used by tortoises to balance the concentrations of salts in their blood, and is absolutely crucial for their survival in the desert. Tortoises are only able to replenish this water supply a few times a year during brief and sporadic thunderstorms. Because tortoises are apt to void their bladders when disturbed, they should never be startled or stressed by picking them up or turning them over.