How Animals Survive in the Desert
The Desert Food Chain Part 4
Like plants, called producers, animals, called consumers, have developed complex ways to survive the prolonged droughts and high temperatures of the Southwestern deserts.
Cacti, yuccas and agaves have developed specialized stem or leaf structures that store the water necessary to see them through drought and heat. Some shrubs become dormant, effectively going to sleep, dropping their leaves and stems to reduce their needs for water during periods of drought and heat. Other plants, like California poppies, indian paintbrushes or bluebonnets, sprout their seeds only when conditions are ideal, growing into new plants, flowering, and producing new seeds swiftly, avoiding the desert’s full measure of drought and heat.
Animals are mobile organisms and have more specialized tissue structures but less heat tolerance than plants. They have developed their own sets of strategies for acquiring and conserving their water supplies and avoiding or escaping drought and heat.
Acquiring and Managing Water
Many animals take advantage of the water freely available in the Southwest’s few continuously flowing river systems and temporary drainages and ponds. The animals and plants that live along stream banks and marshes, or riparian environments, constitute the most abundant and diverse biological communities in the desert basins. The animals that live in the vast desert areas between the river systems, however, must look to other sources for water.
Some acquire water from the plants or animals they eat.
The large, metallic green scarab called the green fruit beetle is a native of the Chihuahuan and Sonoran Deserts. It feeds on the prickly pear cacti’s juicy fruits, which are a source of moisture for it, as well as nutrition. The desert tortoise, a reptile, takes most of its moisture from its foods, which include grasses, wildflowers and cacti.
The hummingbird takes water and calories from the nectar of flowers. With a heart that throbs at a rate of more than a 1000 times a minute and wings that whir at a rate of 80 beats a second, the hummer uses so much energy that it must visit 1000 flowers a day to get the nectar it needs to survive.
Other animals rely on the creatures they eat for moisture. The tarantula wasp ambushes its spider prey near its burrow. It stings the tarantula, paralyzing rather than killing it. It drags the still-living but now immobile spider home, stuffing it into the earthen hole. It lays its eggs on the spider’s body. When the eggs hatch, the wasp’s larvae feed on the paralyzed and helpless tarantula, taking their moisture and nutrition from the creature’s tissue.
The western rattlesnake absorbs most of its water from its prey, usually small mammals and birds, which it swallows whole. In the course of a year, the rattler will take in an amount of water roughly equivalent to its body weight.
The desert martin, or purple martin, is a migratory bird that arrives in the Sonoran Desert from South America in late spring and nests in the towering saguaro cactus. It gets moisture for itself and its young birds from insect prey.
The roadrunner is often depicted as a silly bird in cartoons but is actually a creature superbly adapted to the desert. It takes its water and nutrition from diverse prey – scorpions, reptiles (even rattlesnakes), small rodents and other birds.
The turkey vulture, a desert scavenger with a wing span of six feet, takes much of its moisture from the dead animal carcasses, or carrion. According to eight-year-old Katelyn Martin in her poem The Road Kill Grill, published in DesertUSA, “Dead meat in the heat for the turkey vulture is a treat.”
Bats, the only winged mammal, usually skim streams or ponds for water. Some desert species of bat however, rely only on insect prey for the moisture they need. The long-nose bat of south-central Arizona and southwestern New Mexico, gets its required moisture from the blooms of saguaro and organ pipe cacti and agaves and, after the flowering season, from the ripe fruit of the cacti.
Rock squirrels live in the rocky arroyos and hills of the northern Chihuahuan and Sonoran deserts. They get water from grasses, juicy vegetation and plant bulbs. The rock squirrel may not even bother to drink water available from nearby ponds and streams.
The tough-snouted, pig-like collared peccary often travels in groups of up to 10 or even 50 animals. Also known as javelinas, they get water from the plants of their diverse diet, a thorny feast that includes various prickly pears, the sotol and the thorny lechuguilla agave.
The agile bighorn sheep, among the heartiest of the larger mammals of the desert, also gets water from its widely varied diet, which includes plants such as mountain mahogany, prickly pear cacti and various yuccas and agaves.
While many desert animals meet their water needs from their diet, others have bodies especially adapted for managing water. A beetle has a hard shell, or external skeleton, that encases its body and reduces moisture loss. The scaly skin of reptiles helps retain moisture. The gila monster, which can eat as much as 100 percent of its body weight, can store enough water in its body to last through a whole winter. Roadrunners can reabsorb water from their own waste. The turkey vulture has very powerful kidneys that allow the bird to dispose of its body waste as solid matter while conserving water. The desert kangaroo rat can convert dry seed matter into water during the process of digestion, and has kidneys designed to dispose of waste while conserving water.
Avoiding and Managing Heat Exposure
Desert animals have developed another range of strategies for dealing with the searing heat, which may reach air temperatures of well over 100 degrees Fahrenheit and soil temperatures of well over 150 degrees.
Many animals take refuge in their relatively cool burrows, well beneath the hot surface during the day, and come out at night to hunt or forage. Arizona’s hairy scorpion, which can grow up to six inches in length, digs burrows as much as eight feet deep to escape the heat. The gila monster, which must maintain a body temperature in the range of 85 degrees, spends much of the summer days in a cool earthen burrow, one probably stolen from a packrat. The burrowing owl and the black-throated sparrow will take over rodent's burrows to get relief from the desert sun. Various mammals, from rodents like the desert kangaroo rat to larger animals like skunks and foxes dig their own burrows to serve as retreats from the heat of summer days. Some animals, various ground squirrels for example, spend most of the summer in their burrows, living underground for almost the entire season of heat.
All manner of other animals simply seek out the relative coolness of whatever shade they can find in the desert. Some birds cool themselves by panting to cause the water in their throats and mouths to evaporate, carrying heat away from their bodies and into the air. A turkey vulture expels waste onto its own legs, depending on the evaporation of the moisture to carry away body heat. Some birds migrate to cooler regions or retreat to mountain elevations to avoid the summer heat. The mule deer, the collared peccary and other animals may move to higher and cooler country. The desert bighorn sheep may seek the coolness, not of burrows, but of caves in the mountain foothills during the heat of summer.
Many desert animals have bodies especially adapted to withstand heat. Birds often have light-colored plumage and animals, light-colored coats, which tend to reflect rather than absorb heat. Others have few sweat glands so they can avoid losing water by perspiration. The black-tailed jackrabbit has very large ears that disperse the animal’s body heat into the desert air.
Then Comes the Night
After spending the day in refuge from the summer heat, desert animals begin to emerge as the sun descends in the west and the air and soil temperatures begin to fall. Moths show up to begin their business of pollinating night-blooming plants. The wolf spider climbs from his burrow to scout his territory and begin his hunt. The rattlesnakes and the gila monster start their evening rounds. The mammals begin their business. Often, in the darkness, the coyotes yip excitedly as they close in on a black-tail jackrabbit or a desert cottontail. It's nighttime when the desert comes to life.
by Jay W. Sharp
Food Chain Introduction
How Do Green Plants Manufacture Their Own Food?
How Do Desert Plants Survive?
How Do Desert Animals Survive?
The Arithmetic of the Food Chain
The Classification of Desert Plants & Animals
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