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A xerocole (), is a general term referring to any animal that is adapted to live in a desert. The main challenges xerocoles must overcome are lack of water and excessive heat. To conserve water they avoid evaporation and concentrate excretions (i.e. urine and feces). Some are so adept at conserving water or obtaining it from food that they do not need to drink at all. To escape the desert heat, xerocoles tend to be either Nocturnality or crepuscular (most active at dawn and dusk).
Desert insects use a similar method, as their cuticles are to prevent water from escaping; however, at critical temperatures (ex. for cockroaches), the wax molecules in the cuticle rearrange to become permeable and permit evaporative cooling.
Amphibious xerocoles, such as species of the frog genus Phyllomedusa, have wax-like coatings on their skin to reduce water loss. The frogs secrete lipids from glands in their skin: when their skin begins to dry out, they move their limbs over the glands on their backs, and wipe the lipids over their bodies. Other desert amphibians, such as the frog genus Cyclorana, avoid desiccation by burrowing underground during dry periods and forming a cocoon from shed skin: rather than being sloughed off, the skin remains attached to create the cocoon. As skin layers amass, water impermeability increases.
Some animals pour bodily fluids on themselves to take advantage of evaporative cooling. Xerocole birds such as , New World vultures, and ibis urinate on their legs, while desert tortoises sometimes salivate on their neck and front legs to keep cool. Similarly, many rodents and marsupials lick themselves to spread saliva, though this only remains effective for a short time, and requires the fur to become very damp.
Desert amphibians can store more nitrogen than aquatic ones, and do so when not enough water is available to excrete the nitrogen as urea. The Hyperolius can store excess nitrogen in iridophore, pigmented granules in its skin, by converting the nitrogen to guanine, which makes up the majority of the iridophores' composition.
Reptiles, birds, insects, and some amphibious species excrete nitrogenous waste as uric acid rather than urea. Because uric acid is less toxic than urea, it does not need to be dissolved in water to be excreted (as such, it is largely insoluble).
Seed-eating rodents maintain a low metabolic rate to reduce water lost to respiration (and to prevent their burrow from overheating). Rodent mothers produce concentrated milk for their young, and then eat their young's dilute urine and feces to regain some of the water that was lost. Desert canids and kangaroos eat their own young's excrement for the same reason.
The Australian water-holding frog conserves water by retaining urine in the bladder, swelling up like a balloon; it then uses its bladder as a water reserve during the dry season.
Carnivores derive water from their prey's meat and blood. Insectivores, such as the aardwolf (a type of hyena) and the southern grasshopper mouse, are thus largely independent from free water.
Xerocoles obtain a large percentage of their water from the metabolism used to break down their food. The water gained from fat is nearly twice the amount gained from carbohydrates, as the former contains more hydrogen (which determines the amount of water produced). The water gained from metabolism is more than enough to offset the water lost from evaporation in the lungs (which increases due to the need for oxygen to break down food).
Desert animals have less fat than their non-desert counterparts, as fat would act as insulation, so retaining heat. What fat they do have is localized, such as in the camel's hump or the plains bison neck. In terms of fur, however, desert animals have thick insulating coats that impede the conduction of heat towards the body. The coats are not uniformly distributed, but rather leave sparsely covered patches called "thermal windows" at the axilla, groin, scrotum, and . Heat can be dissipated from thermal windows via convection and conduction.
Similarly, desert birds have fewer feathers on the underwing and flank – heat stress induces some birds to raise their wings, increasing the surface area of exposed skin. Birds adjust their feathers to create or dissipate an insulating layer, as typified by the ostrich. At high temperatures, the ostrich elevates its long dorsal feathers to create a barrier against solar radiation while allowing air to move across the skin's surface. In the cool nights, the feathers lower and interlock, trapping an insulating layer above the skin.
Ectotherms also use burrows as a means to keep warm in the cold desert nights. As ectotherms are usually small and unable to store their own body heat, they quickly take on the external temperature of the environment, which necessitates controlled microenvironments. For example, while reptiles are able to operate at temperatures exceeding optima, they become sluggish when cold. As such, they spend their nights in burrows or crevices, where they create warm environments by quickly generating metabolic heat. (2005). 9780521021418, Cambridge University Press. ISBN 9780521021418 Desert lizards usually use other animals' burrows to meet their purposes.
Many xerocoles, especially rodents, estivate in the summer, becoming more dormant. Some desert amphibians estivate underground for over a year at a time. Unlike hibernation, which leads to a state of torpor, estivation induces lethargy, and can go unnoticed in some animals if their body temperature is not measured.
Most desert lizards also have a black peritoneal lining in their abdominal cavity to absorb UV radiation and prevent it from damaging internal organs.
Shade under shrubbery provides resting spots for diurnal lizards, nesting sites for birds, as well as temporary oases for diurnal rodents, who skirt among shady spots. Large animals such as camels and carnivores also spend the hottest parts of the day under shade.
The three main vulnerabilities against the sand are through the eyes, ears, and nose. To keep sand out of their eyes, xerocoles including reptiles and birds, and some amphibians and mammals have a nictitating membrane in their eyes: a third, transparent eyelid that protects the cornea from blowing sand and can dislodge it from the eye. Reptiles also have eyes the size of pinholes or protected by valves. To keep sand out of their ears, mammals such as the camel and the sand cat have long hairs protruding from them. The camel and the saiga antelope also have adaptations to protect their noses from sand: the former has narrow nostrils it can close, and the latter has a large nose with its nostrils set wide apart and far back to prevent sand from entering when grazing. Reptile diggers have nostrils that face upwards instead of forwards for the same reason.
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