Avoiding Heat

Certain species of birds breed in the spring when it is cooler. Then they leave the desert for cooler areas. The Costa's Hummingbird, a purple-crowned and purple-throated desert species, begins breeding in late winter, then leaves in late spring when temperatures become extreme. 

Many birds are active mostly at dawn and at sunset, retiring to a cool, shady spot for the remainder of the day. Some birds, such as the kingbird, continue activity throughout the day, but always perch in the shade.

Rattlesnakes and Gila Monsters are crepuscular, that is, they are active only at dusk and again at dawn. For this reason, humans seldom see them. 

Many animals are completely nocturnal, active only in the cooler temperatures of the night. Bats, many snakes, most rodents and some larger mammals like foxes and skunks, are nocturnal, sleeping in a cool den, cave or burrow by day.

Some smaller desert animals burrow below the surface of the soil or sand to escape the high temperatures at the desert surface. These include many mammals, reptiles, insects and all the desert amphibians. Rodents may plug the entrances to their burrows to keep out hot air.

When the days become too hot and the vegetation too dry, a few desert animals such as the Round-tailed Ground Squirrel sleep away the hottest part of the summer. (They also hibernate in winter to avoid the cold season.)

Desert Toads remain inactive (dormant) deep in the ground until the summer rains fill ponds. They then come out, breed, lay eggs and replenish their body with food and water for another long period. 

Certain desert lizards are active during the hottest seasons, but move extremely rapidly over hot surfaces, stopping in cooler "islands" of shade. Their legs may be longer so they absorb less surface heat while running.

Dissipating Heat

Some animals dissipate heat in various ways. Owls and nighthawks gape open-mouthed while rapidly fluttering their throat region to evaporate water from their mouth cavities. (Only animals with a good supply of water from prey can afford this type of cooling, however.)

The bodies of many desert mammals have evolved differently from their relatives in cooler regions. The enormous ears of jackrabbits, with their many blood vessels, release heat when the animal is resting in a cool, shady location. 

Because the Turkey and Black Vultures are dark in color, they absorb much heat in the desert. So they excrete urine on their legs, cooling them by evaporation. This behavior, is shared with their relatives the storks, successful birds of the African deserts. Both vultures and storks may escape the hot midday temperatures of the desert by soaring high in cooler air.

Many desert animals are paler in color than their relatives elsewhere in more moderate environments. Pale colors may be seen in feathers, fur, scales or skin. Pale colors not only ensure that the animal takes in less heat from the environment, but help to make it less conspicuous to predators.