All animals face the same problems in adapting to the desert. They must find shelter from daytime heat and nighttime cold, as well as find food and water, which are often scarce. Yet, in spite of these extreme conditions, most animal species are represented in the desert environment, even some we typically associate with temperate or wet surroundings.
Animals without backbones are called invertebrates. They include simple desert animals such as worms, and more complex animals such as the locust. Certain groups of invertebrates must spend part of their lives in water. Generally speaking, these types are not found in deserts. One exception is the brine shrimp, an ancient species that can live in desert salt lakes. Other exceptions are certain species of worms, leeches, midges, and flies that live in the fresh water of oases and other waterholes.
Most invertebrates are better adapted to desert life than vertebrates. Many have an exoskeleton (an external skeleton, or hard shell, made from a chemical substance called chitin [KY-tin]). Chitin is like armor and is usually waterproof. It also protects against the heat of the desert Sun, preventing its owner from drying out.
Many invertebrates are winged and can fly considerable distances in search of food. Many eat plant foods or decaying animal matter. Some invertebrates are parasites, like the Guinea worm, which lurk at waterholes waiting for some unsuspecting animal to wander by. Parasites attach themselves to the animal's body or are swallowed and invade the animal from the inside.
The arachnids (spiders and scorpions), which are carnivores (meat eaters), seem well suited to desert life. They prey on insects and sometimes, if they are large enough, small lizards, mice, and birds. Scorpions use their pinchers to catch prey, then inject it with venom (poison) from the stinger in their tails. Their venom is dangerous, even for large animals and humans, and can kill. Arachnids do not usually drink water but get what they need from their prey.
Most desert spiders live on the ground rather than on webs, hiding in holes or under stones to escape the heat. The large, hairy, camel spiders, which live in all deserts except those of Australia, are nocturnal, which means they rest during the daytime hours and hunt at night.
Scorpions, too, hunt at night and avoid the heat of the day, taking shelter beneath rocks or burying themselves in sand or loose gravel. Several American and Australian species dig burrows that may reach more than 3 feet (1 meter) below the surface.
Some invertebrates, such as the scorpion, go through a mating ritual. Male and female scorpions appear to "dance," their pinchers clasped together, as they do a two-step back and forth. After mating, the males hurry away to avoid being killed and eaten by the female.
Most invertebrates have a four-part life cycle that increases their ability to survive in a hostile (unfriendly) environment. The first stage of this cycle is the egg. The egg's shell is usually tough and resistant to long dry spells. After a rain and during a period of plant growth, the egg hatches. The second stage is the larva (immature), which may actually be divided into several stages between which there is a shedding of the outer covering, or skin, as the larva increases in size. Larvae have it the easiest of all in the desert, often being able to spend a portion of their life cycle below the ground where it is cooler and more moist than on the surface. Some larvae store fat in their bodies and do not even have to seek food. The third stage of development is the pupal stage. During this stage, the animal often lives inside a casing, in a resting state, which may offer as much protection as an egg. Finally, the adult emerges.
Termites and locusts are both invertebrates found in the desert.
Termites: Termites, found all over the world, build the skyscrapers of the desert. Their mounds, often more than 6 feet (2 meters) tall, are erected over a vast underground system of tunnels. These tunnels usually go as deep as the groundwater so that a water supply is readily available to the termite colony. The mounds, which are made of dirt, decaying plants, and termite secretions that dry rock-hard in the Sun, have many air ducts. As the Sun warms the mounds, they grow very hot. As the hot air inside the mounds rises, cooler air is drawn upward through the tunnels, creating a type of air-conditioning system.
Termites eat plant foods, especially the cellulose (substance making up the plant's cell walls) found in woody plants.
Termites have an elaborate social structure. A single female—the queen—lays all the eggs and is tended to by workers. Soldier termites, equipped with huge jaws, guard the entrances to the mound. Soldiers cannot feed themselves, and the workers must tend to them, as well.
Locusts: Locusts are found in the deserts of northern Africa, the Middle East, India, and Pakistan. Similar to grasshoppers in appearance, they have wings and can fly, as well as leap, for considerable distances. For years they live quietly, nibbling on plants and producing a modest number of young. Then, for reasons not completely understood, their numbers increase dramatically. Suddenly, great armies of locusts emerge, hopping or flying through the desert in search of food. Eating every plant in sight, these swarms may travel thousands of miles before their feeding frenzy ends. In a short time, the hordes die off and locust life returns to normal. However, the devastated landscape they leave behind may take years to recover.
Amphibians are vertebrates (animals with backbones) that usually spend part, if not most, of their lives in water. Unlikely as it seems, such animals can be found in a desert. Frogs and toads both manage to survive in significant numbers in desert environments.
The short, active portion of their lives occurs during and immediately after the seasonal rains, when pools of water form. Mating, egg-laying, and young adulthood all take place in these pools. Those that survive into maturity leave the pools and take their chances on the desert floor where they are able to spend a few weeks feeding on both plants and insects. They must find shade, however, or risk dying in the heat of the Sun.
Frogs and toads feed on algae, plants, and freshwater crustaceans such as tiny shrimps that manage to survive in egg or spore form until brought to life by the rains. Frogs that eat the meat of crustaceans while they are tadpoles often become cannibals as they mature, eating their smaller, algae-eating brothers and sisters. If the rainy season is short, the cannibals have a better chance of survival because they have more food choices. If the rainy season lingers, however, the smaller tadpoles have a better chance because the cannibals can't see their prey as well in muddy waters churned up by the rains, but the plant-eaters receive an increased supply of algae.
During the hottest, driest seasons, amphibians go through estivation (ess-tih-VAY-shun), an inactive period. While the soil is still moist from the rain, they dig themselves a foot or more into the ground. Only their nostrils remain open to the surface. Normally, their skin is moist and soft and helps them absorb oxygen. During estivation, however, the skin hardens and forms a watertight casing. All the animal's bodily processes slow down to a minimum, and it remains in this state until the next rainfall, when it emerges. When water is scarce, Australian Aborigines (native peoples) dig up estivating frogs or toads and squeeze the animal's moisture into their mouths.
Mating and egg-laying for amphibians must take place in water, because male sperm are deposited in the water and must be able to swim to the jelly-like eggs in order to penetrate them. As the young develop into larvae and young adults, they often have gills. Therefore, they too require a watery habitat. If there is not enough rain for pools of water to form, amphibian populations may not survive.
Of all the animals, reptiles are perhaps most suited to living in the desert. Those most commonly found there are snakes, lizards, and some species of tortoises. Their scaly, hard skin prevents water loss, and their urine is almost solid, so no water is wasted.
Reptiles are cold-blooded, which means that their body temperature changes with the temperature of the surrounding air. This may actually help them live in the desert. Early in the day, they expose as much of their bodies as possible to the Sun for warmth. As the temperature climbs, they expose less and less of their bodies. During the hottest period of the day, they find shade or a hole in which to wait for cooler temperatures. During the chilly nights, although they become sluggish, they do not have to waste energy keeping their body temperatures up as most mammals and birds must.
Besides being cold-blooded, some species of lizards have specially developed clear membranes in their lower eyelids that cover the entire eye and protect the eye from lost moisture.
Snakes have no legs. They move using special muscles that flex their flat belly scales forward and backward. Ridges on their scales grip the ground and pull them along. Some rattlesnakes, like the sidewinders of North American deserts, manage to move diagonally by coiling into a kind of S-shape, and propel themselves by pushing with the outside back portion of each s-shaped curve.
The diet of lizards varies, depending upon the species. Some have long tongues with sticky tips that are good for catching insects. Many are carnivores that eat small mammals and birds. The water they need is usually obtained from the food they eat.
While most lizards hunt food during the day, the gila monster, found in the southwestern United States, looks for reptile eggs and baby animals after dark. Making the most of its opportunities, the lizard stuffs itself. During periods when food is scarce, its body draws on extra nutrients stored as fat in its tail, which can double in size after a big meal.
All snakes are carnivores, and one decent-sized meal will last them for days or weeks. In the desert, they make good use of their eyes to hunt during the cool nights when their prey are most active. Snakes cannot close their eyes because they have no eyelids. However, a transparent covering protects their eyes from the dry air, dust, and sand. Because they often hunt underground they have adapted to detecting ground vibrations. Many desert snakes bury themselves in the sand so that only their eyes and flickering tongues are visible. There they wait. The more evolved snakes kill their prey with venom (poison).
Although they are commonly thought of as jungle dwellers, boa constrictors and pythons (also a species of constrictor) also live in the desert. Constrictors strike their prey, hold it with a mouthful of tiny teeth, then wrap their body around it like a coil. Gradually, the prey suffocates and the constrictor swallows its meal whole, gradually working it into its stomach with its hinged lower jaw and strong throat muscles.
Lizards and snakes retire to the shade during the hottest hours of the day, where they can escape the Sun. Only a few make their own burrows. Most take over the abandoned burrows of other animals, find shelter in rock crevices, or bury themselves in the sand.
Desert tortoises obtain some shade from the Sun with their thick outer shells. But, most of the time they escape the heat of the day by retreating to burrows, which they have dug. In the spring and autumn, when the days are not excessively warm, the tortoise ventures out during the day to forage for food. However, during the summer, they forage for food at night when it is cooler, remaining in burrows during the day. In the winter, tortoises hibernate (become dormant) in a second burrow, which they have dug.
The eggs of reptiles are leathery and tough and do not dry out easily. Some females remain with the eggs, but most bury them in a hole. Offspring are seldom coddled and are left to hatch by themselves. Once free of the eggs, the babies dig themselves out of the hole and begin life on their own.
Snakes are less common in deserts than lizards. Common desert snakes include the gopher snake, horned viper, Gaboon viper, rattlesnake, and cobra. The cobra is found in Africa and India.
Common lizards include the gecko—which can survive long periods without food by living on stored fat—the skink, the bearded dragon, the iguanid lizard, and the monitor lizard.
All deserts have bird populations. Tropical and subtropical deserts are visited twice each year by hundreds of species of migratory birds traveling from one seasonal breeding place to another. These migrators include small birds such as wheatears, as well as larger species such as storks and cranes. Some species know the route and where to find food or water. Others fly at night, when it is cool. However, migrators are not true desert birds. They cannot survive for long periods in the desert as can birds for which the desert is home.
Because birds have the highest body temperature of any animal—around 104°F (40°C)—they do not need to lose body heat until the desert temperature is greater than their own. This makes desert life easier for them than for mammals, which must lose heat regularly during the warmest months, usually by panting or sweating.
Feathers protect birds not only from the cold in winter but from the Sun and heat. Air trapped between layers of feathers acts as insulation. Birds do not sweat but, by flexing certain muscles, can make their feathers stand erect. This allows them to direct cooling breezes to their skin. Those having broad wing spans, such as eagles and buzzards, can soar at high altitudes and find cooler temperatures.
Birds are found in greater variety and numbers around oases and waterholes where there is an ample supply of water, seeds, and insects. Some, like the Australian scarlet robin, often drink water. Birds that live in the desert itself are able to fly long distances in search of food or water. Some birds become nomads, following the rains from habitat to habitat. However, birds usually require less than 10 percent of the amount of water needed by mammals. For this reason, many, like shrikes and some wheatears, can obtain enough moisture from the seeds, plants, and insects that they eat and do not need an additional water source. The same is true of vultures and birds of prey, which obtain water from the flesh of animals. Also, birds' kidneys are very efficient in their ability to extract water, and their urine is not liquid but jelly-like.
During the hottest part of the day, most desert birds rest by roosting in the shade or in underground burrows. During excessively hot or dry periods, birds can simply fly to more comfortable regions. It has been estimated that one-third of Australian birds are constantly on the move to escape the heat.
Because the desert is home to so few trees, many desert birds build nests in rock crevices, in abandoned burrows, or on the ground in the open. Those that build on the ground may put walls of pebbles around the nest which act as insulation and reduce the force of the wind.
Except in Australia, desert birds appear to breed as other birds do—according to the seasons. In Australia, they adapt their breeding habits to periods of rainfall, and breeding cycles may be years apart.
Although birds are free to fly away from the heat during the rest of the year, during the breeding cycle they must remain in the same spot from the time nest building begins until the young birds can fly. This is usually a period of many weeks.
Normally, the parents sit on the nest to protect the eggs from heat or cold. During very hot weather, the parents may stand over the nest to give the eggs or the nestlings shade.
Common desert birds include ground birds and birds of prey.
Ground birds: "Ground" birds are not hunters or scavengers (animals that will eat decaying matter) but obtain most of their food from plants and insects. They have strong legs that enable them to dart around on the ground without tiring.
In Asia, Africa, Australia, and the Arabian Peninsula, families of thrushes called chats are common. Varieties of chats live at many different altitudes, including those over 13,000 feet (4,000 meters). They are found in both arid and semiarid regions, and their diets and habits vary according to their location.
Wrens are also common in desert habitats all over the world. Wrens eat insects, although those in North American deserts also eat seeds and soft fruits. Cactus wrens, as their name implies, live among prickly desert plants where they build their nests among the spines.
A small desert bird that is popular as a pet is the parakeet, or budgerigar. Originally from Australia, parakeets normally live in huge flocks containing tens of thousands of birds. During years when food is plentiful, a flock may number in the millions. Parakeets prefer seeds and are nomads, often traveling from habitat to habitat in search of the seeds of annuals that bloom after a rainfall.
A desert bird that became famous as a cartoon character is the roadrunner, found in the southwestern United States. Their name is well earned, for roadrunners can scurry over the desert floor for long stretches at speeds of about 13 miles (20 kilometers) per hour. Roadrunners are carnivores and are known to come running at the sound of a creature in trouble.
The largest ground birds found in deserts are members of the bustard family. The houbara bustard is found in the Sahara and the deserts of central Asia. It is about 2 feet (60 centimeters) tall and weighs as much as 7 pounds (3 kilograms). Although houbaras depend primarily upon plants for food, they also eat invertebrates and small lizards. Houbaras can run fast—up to 25 miles (40 kilometers) per hour—and seldom fly.
Birds of prey: Birds of prey are hunters and meat eaters. They soar high in the air on the lookout for small animals for food. Their eyesight and hearing are usually very sensitive and enable them to see and hear creatures scurrying on the ground far below.
Several species of falcons live in semiarid regions, but the true desert falcon is the prairie falcon of North America. Prairie falcons hunt for other birds such as larks and quail, and small mammals such as rabbits and prairie dogs. When food is scarce, they will also eat insects and reptiles. A falcon attacks its prey by diving at the head and trying to seize the head in its talons. Prairie falcons do not build their own nests. Instead, they move into the abandoned nests of other birds or use a hollow in the rock.
Owls live on the edges of deserts. The largest, the eagle owl, measures 27 inches (68 centimeters) in length with a wingspan of 66 inches (168 centimeters) and has the power to attack small deer. The smallest owl, the elf owl, hunts invertebrates and small mammals such as mice and gerbils. This owl is about 5 to 6 inches (12 to 15 centimeters) long and weighs 1.25 to 1.75 ounces (35 to 55 grams). Most owls hunt in the evening or at night when their extraordinary eyes and superior hearing allow them to find their prey.
The bird most often pictured in the desert is the vulture, usually waiting patiently while some poor creature dies of thirst. However, most of the world's vultures are not really desert birds, although they do spend much time hunting in desert regions. They soar high in the air, circling and looking for carrion (dead animals), which their excellent eyesight allows them to see easily. When one bird sees a potential food source it begins to descend, and the other vultures follow.
Many mammals live in the desert. More than 70 species live in North American deserts alone. Among all of these species, only monkeys and apes are rarely seen.
Mammals, too, must prevent the loss of moisture from their bodies in the desert. The urine and feces of many desert mammals are concentrated, containing only a small amount of water. Also, small desert mammals, such as rodents, do not sweat. They usually manage to lose enough heat through their skins. During the hottest times, they burrow underground. Some estivate during summer months.
Medium-sized mammals, such as rabbits and hares, do not burrow or estivate; although they will use another animal's burrow to escape from immediate danger. They also have no sweat glands and cannot keep cool by sweating, although some heat escapes from their large ears. Hares and rabbits stay in whatever shade they can find during the hottest time of day. The quokka, a rabbit-like marsupial (a mammal that carries new offspring in a pouch) from Australia, copes with the heat by producing large amounts of saliva and licking itself. It is not known how the quokka makes up for this water loss.
Larger grazing animals, such as gazelles, can sweat, which helps them tolerate the heat. Some carnivores, such as coyotes, release body heat by panting (breathing rapidly through their mouths). However, this results in lost moisture. True desert dwellers, like the mongoose, the meerkat, and the hyena, avoid the midday heat by retiring to underground dens.
Some small mammals eat plant foods and insects; others, like the desert hedgehog, eat bird and reptile eggs and young. In Australia, a tiny mole no more than 8 inches (20 centimeters) long eats at least its own weight in insects and young lizards every day. Many small mammals do not need to drink water as often because they obtain moisture from the food they eat.
Large grazing animals need to drink and require a water source to replace the moisture lost in sweating. A few, however, such as the Arabian gazelle and the Nubian ibex, seldom drink water. They, too, obtain what they need from the plants they eat. Because they are mobile, grazing animals can travel to areas where rain has recently fallen. In temperate climates, most grazing animals live in large herds. The desert food supply, however, will not support such numbers, and groups are usually very small.
Carnivores such as mountain lions and coyotes, do not live in the deep desert but remain on the desert fringes where a supply of water can be more readily found. Although carnivores obtain much of their moisture requirements from the flesh of their prey, they still need to drink.
Small mammals remain in burrows during the day. The air inside a burrow is up to five times more humid than the outside air, and this helps the animal prevent moisture loss.
Medium-sized hares and rabbits do not live in burrows but seek shelter in the shade of plants or rocks and in shallow depressions. Grazing animals, too, look for shade during the midday heat. Young animals may lie on the ground in the shade created by the adults.
Carnivores dig their own dens, which may consist of many tunnels to accommodate a family clan. The males mark their territories with scent, usually that of urine.
Young mammals develop inside the mother's body where they are protected from heat, cold, and predators, although the extra weight can make it difficult for the pregnant females themselves to escape danger. Female mammals produce milk to feed their young which, in the desert, presents a problem in lost moisture. Those that live in dens must remain nearby until the young can survive on their own, which can make survival for both mother and young during drought conditions more difficult.
Mammals commonly found in deserts include the kangaroo, the camel, and the hyena.
Kangaroo: Probably the most well-known grazing animal of Australia is the red kangaroo. Although the kangaroo will hop for long distances in search of food, water is less of a problem as they get much of the moisture they need from grasses. Also, their kidneys are efficient and produce a concentrated urine.
The kangaroo's strong legs allow them to move as fast as 20 miles (30 kilometers) an hour. Each hop can carry them as far as 25 feet (8 meters). Kangaroos are marsupials, which means that females carry their young in a pouch on their abdomen. Females with young in their pouches are seldom able to travel fast. If the female is in danger and the baby is too heavy, the mother will dump the baby out in order to escape. This may seem cruel, but if she is caught the baby will die anyway. If she escapes, she will breed again.
Camel: Of all animals, camels are the ones most people associate with the desert. The Bactrian camel has two humps and lives in the deserts of central Asia. The one-humped Arabian camel, called a dromedary, lives in the Arabian and Sahara Deserts. Camels are well adapted for desert life. They can travel almost 100 miles (160 kilometers) in a day, for as long as four days, without drinking. When they do drink, they can take in more than 20 gallons (100 liters) in just a few minutes.
At one time it was believed that camels stored water in their humps. This, however, is not true. The hump contains fat, which is used up during long journeys and which, in lean times, may shrink. Camels also have strong teeth and the membranes that line the insides of their mouths are tough, allowing them to eat almost anything that grows in the desert, even the thorniest plants. They can drink bitter, salty water that other animals cannot tolerate.
Their fur is thick and, during the hottest seasons, molts (falls out) and is replaced by new, thinner hair. Camels can sweat to reduce body temperature, but their body temperature is not constant and varies depending upon surrounding air temperatures. Their eyes have long protective lashes, and their nostrils can be closed to keep out blowing sand. Their padded, two-toed feet are well insulated against the hot desert floor.
Camels can no longer be considered wild animals, and it is doubtful that any wild groups still exist. They have been thoroughly domesticated (tamed) and are used by humans for transportation and other needs. Their ability to travel long distances and carry up to 600 pounds (270 kilograms) makes them useful.
Hyena: Hyenas are members of the dog family and have one of the strongest sets of jaws of any animal. They range over the deserts of Africa and Arabia, hunting in packs for antelope and other game, or stealing the meal of some other carnivore. They also eat carrion and, occasionally, plant foods. Although they are not particularly fast, they do not give up easily, and may simply wear out their prey, which collapses beneath the snarling pack. Hyenas live as part of a clan in dens they dig themselves.
As in other biomes, many desert animal species are threatened.
A desert antelope with beautiful horns, the addax has been greatly reduced in numbers by Saharan nomads who believe its stomach contents have healing powers. Its skin, too, is valuable, for it is believed to have the power to ward off attacks from snakes and scorpions.
After World War II (1939-45), when dichlorodiphenyl-trichloroethane (DDT) and other dangerous pesticides were in common use, aplomado falcons shrank in number. These small falcons lived in desert areas of Mexico, Texas, and Arizona, but are no longer found north of Mexico. The poisons were used to kill grasshoppers that were devouring grasses and other vegetation. Grasshoppers are part of the falcons' diet, and as the birds ate the contaminated insects the poison also killed the falcons. It is hoped that the number of falcons will increase now that DDT is banned.
The condor is one of the world's rarest birds. When early settlers slaughtered deer herds for food, they reduced the condor's food supply. Later, cattle ranchers set out poison baits to kill wolves and coyotes, and the poison also killed the condors who ate the dead animals. California condors are now protected, but only a few dozen survive. Some birds have been bred in captivity, however, so there is a chance that the species can be increased.
The beautiful spiral horns of the Arabian oryx are prized by hunters looking for trophies. By 1960 the Arabian oryx were reduced to only about a dozen animals. In 1961 they became protected and several hundred were bred in zoos. After 1982 many of the zoo-bred animals were reintroduced into the wild.
Source: "Desert." U·X·L Encyclopedia of Biomes, Vol. 1. U·X·L, Detroit: 2000.