Even the driest and most inhospitable desert is home to a wide range of animals, each with a series of adaptations that allow it to live in hot, dry conditions. These adaptations allow animals to either avoid or dissipate heat and to absorb or conserve water. Desert animals are often small to reduce the amount of water they need and the space they need to shelter from the sun.
Many desert animals are nocturnal and come out to forage only at night, or are crepuscular and feed at dawn and dusk. During the heat of the day, they stay out of the heat in burrows or rock crevices. Even desert lizards that are active during the heat of the day seek out shade whenever they can. Many species migrate away from deserts during the hot, dry seasons, returning after rains.
Some animals, such as frogs and even fish, which you would not expect to find in the desert, survive by aestivating during the dry season and waking up after rains to feed and breed. Primitive lungfish can aestivate in the mud under dried-out desert lakes for several years. In Australia, the water-holding frog Litoria platycephala can aestivate for several months under the desert soil. Recently, the Madagascan lesser dwarf lemur, Cheirogaleus medius, has been found to be the first mammal that is able to aestivate.
Many desert animals are pale coloured, which means that they do not absorb as much heat from the sun. Others, such as the fennec fox, Vulpes zerda, have large ears which radiate heat away from their bodies. Some desert birds, like storks and vultures, defecate on their own legs, allowing the liquid in the faeces to evaporate and cool them down. This process is called urohydrosis.
As well as extreme heat, desert animals must cope with the lack or water in their habitats. Desert reptiles burrow down into damp soil and can absorb water through their skin, while rodents block up the entrance to their burrows to keep the air inside moist and save water. Birds and reptiles have an advantage over mammals as they are able to excrete solid uric acid rather than water-soluble urea like mammals. Mammals, therefore, have to use more water to get rid of their bodily waste.
Many desert animals, such as camels, have the ability to drink a lot of water when they find it and then to store water as fat for the future. American kangaroo rats of the genus Dipodomys are able to metabolise their own water from dry seeds and never need to drink at all. In Namibia, the fog-basking beetle (Onymacris unguicularis) is able to collect and drink water from sea mists that blow over its desert habitat. Also in Namibia, the shovel-snouted lizard (Meroles anchietae) has evolved a special pouch off its intestine that allows it to store water for long periods.