Keep Your Cool

By Terry Chenoweth

The hot summer sun beats down all day on the American Southwest deserts, where the air temperature often reaches 110º F (43º C) and can go as high as 120º F (49º C). On the desert floor it can be much hotter, sometimes as high as 190º F (88º C). Yet certain animals are able to survive in this harsh environment. Contrary to popular belief, however, even snakes and lizards would perish at temperatures little higher than those fatal to human beings if it weren’t for these desert animals’ ability to adapt to the scorching conditions.

Many desert lizards and snakes have a shiny skin that reflects some of the sun’s rays, but this alone is not enough to save them during the hottest months. Horned lizards flatten their bodies and dig into loose, shaded sand to rid themselves of excess heat. Fringe-toed lizards likewise bury themselves in the loose sand, both to release heat and to escape predators. Instinctively they dig into the lee side of sand dunes. This way they will not be deeply buried as the wind shifts the sands.

Other lizards, much like barefoot humans, run across the hot sand on tiptoe. When they stop momentarily, they hold themselves stiff-legged to keep their bodies as high off the ground as possible. Some have even been observed lifting one foot and then another to gain momentary relief from the burning sand.

On the shores of Southern California’s sultry Salton Sea, white pelicans nest in temperatures as high as 110º F (43º C), yet their eggs can only survive below 105º F (41º C). To protect the eggs until they become nestlings, one of the parents will periodically wade out to splash in the shallows. On returning, it will relieve its mate and wet the eggs with its breast feathers and shade the eggs with its body.

Pelicans and other desert birds, such as vultures, can temporarily escape the heat by flying to high altitudes and riding the cooler wind currents.

The large ears of a jackrabbit aren’t just for hearing. Its ears are filled with tiny blood vessels that radiate body heat when the air temperature is less than its body temperature. But when the air temperature rises, the blood flow to and from its ears is mostly shut off.

Antelope ground squirrels are an exception to most desert dwellers. They continue to feed actively even in the hottest part of the day. To shed their excess heat, they periodically flatten themselves against the cooler earth of shady ground. Within a few minutes they are again actively feeding in the sun.

While these methods of survival work for some animals, most desert residents attempt to escape the heat by burrowing underground, where daytime temperatures are considerably cooler. About 70 percent of all desert animals live below the ground, while less than 10 percent of forest animals live in burrows.

Kangeroo rats are industrious diggers that live in a maze of tunnels and subterranean rooms. Their sleeping chambers can be as much as two feet underground. Succeeding generations of the largest kangaroo rats leave mounds of excavated earth two or three feet high and up to fifteen feet in diameter. During the day the rats keep the tunnels loosely plugged to help shut out the heat.

Desert tortoises dig two kinds of burrows. One large den will hold several of the tortoises as they hibernate through the winter. In the summer they dig individual tunnels to a depth of several feet.

Most desert burrowing animals are nocturnal, avoiding the daytime heat by sleeping through it. Some animals that normally hunt during the day in other climates become nocturnal in the desert. Other denizens of this arid world feed only at dawn and dusk.

Several kinds of snakes and small mammals use burrows for estivation, a state of limited activity similar to the hibernation of certain animals in colder climates.

The adaptive ability of creatures to survive in a sometimes hostile environment is truly one of the most remarkable aspects of life in the animal kingdom.

Illustrated by Shauna Mooney