Animal Survival in the Desert

Among the thousands of desert animal species, there are many remarkable behavioral and structural adaptations developed for avoiding excess heat. Equally ingenious are the diverse mechanisms various animal species have developed to acquire, conserve, recycle, and actually manufacture water.

Certain species of birds, such as the Phanopepla, breed during the relatively cool spring, then leave the desert for cooler areas at higher elevations or along the Pacific coast. The Costa's hummingbird begins breeding in late winter and leaves in late spring when temperatures become extreme. Many birds, as well as other mammals and reptiles, are crepuscular, meaning they are active only at dusk and again at dawn. Many animals, including bats, many snakes, most rodents, and some larger animals such as foxes and skunks, are nocturnal, restricting all their activities to the cooler temperatures of the night, and sleeping in a cool den, cave, or burrow by day. A few desert animals, such as the round-tailed ground squirrel, sleep away the hottest part of summer and also hibernate in winter to avoid the cold season. Yet other animals, such as desert toads, remain dormant deep in the ground until the summer rains fill ponds. They then emerge, breed, lay eggs, and replenish their body reserves of food and water for another long period.

Various mechanisms are employed to dissipate heat absorbed by desert animals. Many mammals have long appendages to release body heat into their environment. The enormous ears of jackrabbits, with their many blood vessels, dissipate heat when the animal is resting in a cool, shady location. Their close relatives in cooler regions have much shorter ears. New World vultures, dark in color and thus absorbing considerable heat in the desert, excrete urine on their legs to cool them by evaporation, and circulate the cooled blood back through the body. Many desert animals are paler than their relatives elsewhere, ensuring that they not only suffer less heat absorption, but also are less conspicuous to predators in the bright, pallid surroundings.

The mechanisms by which water is retained by desert animals are even more elaborate. Reptiles and birds excrete metabolic wastes in the form of uric acid, an insoluble white compound, wasting very little water in the process. Other animals retain water by burrowing into moist soil during the dry daylight hours. Some predatory and scavenging animals can obtain their entire water needs from the food they eat. Most mammals, however, need access to a good supply of fresh water at least every few days, if not daily, due to the considerable water loss from excretion of urea, a soluble compound.

Many desert animals obtain water from plants, particularly succulent ones such as cactus and saguaro. Many species of insects thrive in the desert, as they tap plant fluids for water and nectar. The abundance of insect life permits insectivorous birds, bats, and lizards to thrive in the desert. Certain desert animals, such as kangaroo rats, have multiple adaptation mechanisms to acquire and conserve water. First, they live in underground dens that they seal off to block out heat and to recycle the moisture from their own breathing. Second, they have specialized kidneys with extra microscopic projections to extract most of the water from their urine and return it to the bloodstream. Third, and most fascinating of all, they actually manufacture their water metaboli-cally from the digestion of dry seeds. These are just a few examples of the ingenious variety of adaptations animals use to survive in the desert, overcoming the extremes of heat and the paucity of water.

See also: Bats; Birds; Chickens, turkeys, pheasant, and quail; Dogs, wolves, and coyotes; Eagles; Ecosystems; Fauna: Africa; Fauna: Asia; Fauna: Australia; Fauna: North America; Foxes; Frogs and toads; Habitats and biomes; Hibernation; Insects; Lizards; Mice and rats; Nocturnal animals; Rabbits, hares, and pikas; Reptiles; Rodents; Scorpions; Sheep; Skunks; Snakes; Spiders; Squirrels; Thermoregulation; Turtles and tortoises; Vultures; Water balance in vertebrates.

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