By December of most years we’ve retreated from the northern cold, with our journey usually ending in the deserts of the Southwest. Some people go to the deserts only to escape - we return year after year because we love the open spaces, the low humidity, and the many desert creatures that live there year-round.
Many travelers driving through the desert believe it is almost devoid of life. They see a vulture circling on a thermal and wonder how the poor creature gets enough to eat. But those who take time to understand the desert find it well populated. And they find that desert animals have developed surprising ways of living with their harsh surroundings.
All desert creatures must cope with two difficulties: too little water and too much heat. One definition of a desert is an area that receives less than 10 inches of rainfall per year. Another is an area where the local residents call a summer day cool when the temperature reaches only 100 degrees.
One year we tried a summer in the desert. Humans survive inside airtight houses, air conditioners on high, with soft drinks from the refrigerator. Outside, desert life goes on. Now we have even more respect for the resourcefulness of our winter animal friends, having some idea of the adversity they endure while we are gone.
Some animals we see in winter are temporary visitors such as ourselves. Birds flock to the desert warmth, some coming from the far north, and some, such as the cardinal, making a trip downward from nearby mountain ranges. This “vertical migration” is shared with some of the larger mammals such as the deer, javelina, mountain lion, and coyote. But of more interest are the summer survivors, the creatures who have defeated both dryness and heat.
Most surprising are the desert dwellers who depend upon water for their very existence. Toads, for example, seem out of place on the desert , yet they live in areas that see water for only a few months each year. Spadefoot toads spend 10 or more months each year buried underground.
Somehow they sense the summer rains that fill shallow pools with life-giving water, and the desert sings with mating calls. The toads’ eggs take but a few hours to hatch, and then begins the race with time. The newly born must mature to a size such that they can withstand the rigors of hibernation before their puddle-home dries up. Usually, they succeed.
These ephemeral pools of water are also the home of fairy shrimp, tiny creatures that live in puddles which may last only a few days. These shrimp are programmed to lay their eggs when the last of the water begins to evaporate. The adults die, but their eggs live on.
Fairy shrimp lay two kinds of eggs - one type hatches the following season, but the other kind lasts for years. This insures that an unusually dry season won’t kill off all the shrimp. Both kinds of microscopic eggs dry up with the puddles where they were laid, and the wind scatters them across the desert. So fairy shrimp may appear almost anywhere.
Although lizards and snakes are already hibernating when we arrive, we usually see them in the spring before we leave. As coldblooded animals, both snakes and lizards require temperatures near 60 degrees before they can become active. On spring mornings these reptiles sun themselves, regulating their temperature by exposure to the sun’s rays.
As the season wears on toward summer, they start seeking protection from the heat of midday. Watching lizards and their actions can be a general guide as to how hot it is. Early in the day the lizard flattens its body, trying to expose as much surface to the sun as possible. As the lizard warms up, it becomes more active. By midmorning, the lizard’s body temperature may be around 100 degrees, and the warmer the animal gets, the quicker it moves, becoming as much as seven times faster as the day wears on.
But eventually the heat becomes too much for even the lizard, and it holds its body as far above the surface of the ground as its legs will stretch. Finally, it starts seeking shady areas, even retreats underground if it becomes too hot.
The snowbirds of the desert are only there during the winter, and the hibernators come out only toward the end of our desert stay, but our favorite desert animal appears year-round. You have only to look at night.
Dipodomys is his scientific name, but most people know him as the kangaroo rat. A little six-inch creature with an eight- or nine-inch tail tipped with white fluff, the kangaroo rat has rear feet large enough to give him his name. And like the kangaroo, he gets around by jumping. When in a hurry, he seems to almost fly through the air, and his long tail acts as a rudder.
The kangaroo rat is well designed for desert life, since he never needs a drink. Each night he comes out looking for food, and subsists upon dry, woody growth and seeds. His body, by chemical means, turns these materials into the moisture needed to keep him alive.
Finding a kangaroo rat is relatively easy. His tunnel home has a large entrance - five or six inches in diameter - since he enters (and moves around inside) by jumping. The soil around the hole will be covered with fresh tracks. Kangaroo rats are relatively tame, and often let you shine a flashlight on them while they go about their business. You won’t have to look far, since their travels never take them more than 300 feet from home.
During the summer, the kangaroo rat keeps cool by plugging the hole of his home. While the ground temperature above his head may reach 150 degrees, his nest temperature remains in the high 80s. When the sun goes down he unplugs his hole and goes in search of food.
During the winter, we go looking for kangaroo rats on nights with a full moon. A little grain scattered near the hole keeps Dipodomys busy, and the full moon shines through the star-filled sky to let us watch without interfering. An evening’s free entertainment. A visit with a friend. And a reason to return to the desert.
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