Window On Nature
By Lowell & Kaye Christie, F47246
It’s hot outside our home here in the Sierra foothills, but certainly not as hot as it is in the Southwestern deserts. So, let’s see how the wildlife of that arid environment manage to stay alive.
It’s obvious that searing summer temperatures are hazardous to animals, and that only species adapted to extreme heat and lack of water can survive. Having lived 10 miles west of Tucson, Arizona, for several years, we know the feeling of heat coming from the sun, from making physical contact with rocks and soil, and from the constant drying effect of superheated air.
An animal’s survival depends on its ability to keep its body temperature within a rather narrow range. The problem is, extreme summer temperatures last for four to five months of the year.
Some animals leave before the heat becomes too intense; but for others, that’s not an option. They have had to adapt both physically and behaviorally to such temperature extremes.
Examples of escaping the heat are easy to find. After all, around March, human snowbirds begin packing up their motorhomes and hitting the highway. By May, desert campgrounds are just about empty.
The word “snowbird” is an apt one, because the majority of real birds that one may see in the desert during the fall, winter, and spring simply aren’t around during the summer. The lovely phainopepla, for example, would be hard-pressed to survive the summer, given its jet-black plumage. This bird breeds in early spring and beats the heat by flying to higher elevations, or west to the coast. The tiny Costa’s hummingbird follows the same pattern, breeding in late winter, so the parents and chicks can move out before they bake in the summer heat.
Resident birds nearly always restrict their activity to early morning and after sunset. The rest of the day, they stay perched in the shade “” the more green there is, the cooler and moister their surroundings. Several flycatcher species also hang around, doing most of their bug-catching early and late, when the majority of bugs appear. Between forays, they head back to a shady location.
Most mammals and nearly all reptiles also are most active at dusk and dawn. That’s why we humans won’t encounter them often, unless we’re seeking relief under the same shade tree.
A good many desert animals are nocturnal. Bats and a number of other mammal species, as well as reptiles, insects, and all amphibians, doze the day away in their dens or burrows, waiting for nightfall to search for food. Some species, rodents in particular, even plug the entrances to their burrows at dawn, and dig their way out each night.
A few desert animals, such as the round-tailed ground squirrel, estivate in the summer. (Think of it as hibernating from the heat.) You can bet that desert denizens of the human sort welcome their re-emergence, which signals that cooler weather is on the way.
Spadefoot toads also stay deep underground during the blazing days of summer, but they know when to come up. They can feel it when summer rains drum on the desert surface, and they gradually begin digging upward. But they know better than to rush right out of the ground. Only after the rains have filled the ponds can they breed, lay eggs, and replenish their body reserves of food and water.
A few species of desert lizards remain active even during the hottest months, because they use techniques to avoid getting fried. Some move at top speed across hot surfaces, slowing down only when they reach a cool “island” of shade. The legs of some lizard species are longer than those of their non-desert relatives; that way, they absorb less surface heat while running.
A few animals have discovered other interesting ways to dissipate heat. When perched, birds from the owl, poorwill, and nighthawk families gape open-mouthed while rapidly fluttering their throats. It’s quite something to see. The behavior, somewhat similar to a dog’s panting, allows water to evaporate from the bird’s mouth, thus lowering its body temperature. There’s a catch, though “” the gaping does little good unless the bird has recently eaten juicy prey.
Other desert critters, mammals mainly, use a different method to dissipate body heat. The jackrabbit’s enormous ears are dense with blood vessels, which help to release body heat while the animal relaxes in the shade. Their relatives in cooler regions have shorter ears.
Turkey vultures and black vultures are very dark in color, so they absorb quite a bit of heat in the summer. They cool off by urinating on their legs, which lowers their temperature as it evaporates. The cooled blood from the legs is then circulated throughout the body. This behavior, called urohydrosis, also is practiced by storks living in African deserts. Both vultures and storks use another method to escape the searing midday temperatures. They spend the hottest hours soaring high overhead, riding on thermals of air.
Have you noticed how pale, even faded, some desert animals are? Tan is the standard attire, whether in feathers, fur, scales, or skin. Pale colors have two advantages. First, they prevent the animal from absorbing too much heat in the sun. Second, they make it less conspicuous to predators.
Finally, we come to the desert darlings, the kangaroo rats, which use many of the previously mentioned adaptations for survival, plus a few more.
For one thing, they have specialized kidneys to filter out most of the water from their urine and return it to the bloodstream. Even their noses are specially designed to retain water that would otherwise be exhaled when breathing
Finally, kangaroo rats, and a few other desert rodents, are able to manufacture their own water metabolically, while digesting very dry seeds. They are so good at the task, they won’t even drink water when it’s right in front of their noses.