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Wild animals that live in the desert must cope with an extreme climate to survive. These desert-dwelling creatures receive heat from the sun's radiation, convection heat from the stifling air and heat conducted from the soil and rock around them. This intense warmth, combined with scarce hydration resources and rapidly fluctuating temperatures, means that only animals that have adapted to these surroundings can survive.
For birds of the desert, avoiding heat means breeding in the cooler spring and winter temperatures. They are also largely crepuscular, as are most desert animals -- they come out during dawn and dusk, and keep to cool, shady areas during the day. Other desert fauna such as snakes, foxes and rodents avoid heat by living nocturnally, only emerging from burrows at night. Burrowing is another tactic used by desert-dwelling lizards and amphibians; desert toads dig into the sand and remain dormant until summer rains bring cool water.
In addition to learned and instinctual avoidance behavior, animals that live in the extreme heat of the desert have biologically adapted to be better suited to that environment. Desert mammals have evolved long legs, ears and tails that dissipate heat from numerous blood vessels throughout the appendages. Dark-plumed birds such as vultures utilize a method known as urohydrosis; they will urinate on their feet. As the urine evaporates, it cools the feet, then the cooled blood is circulated throughout the rest of the body.
The most common source of water for desert-dwelling creatures is derived from plants, especially succulents. Birds of prey are able to stay hydrated from the blood and water retained in their victims. Small rodents, such as the kangaroo rat, will block the holes of their burrows to recycle the moisture from their own breath. Insects in the desert thrive by tapping stems or leaves for their hydration; benefiting in turn the numerous animals that live on insects, such as bats.
Reptiles and some desert birds do not waste any water in urinating; instead, they excrete an insoluble compound called uric acid. Some desert rodents have unique kidneys that filter most of the water in their blood stream and re-circulate it into the body. Mammals in the desert also sweat much less than mammals in more temperate zones. In desert insects, there is a gland in the rectum that absorbs leftover water, excreting dry pellets as feces.
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