Monday, November 19, 2012

Squirrel Facts: Squirrels of the Desert

When most Americans think of squirrels, we think of the eastern gray, the familiar bushy-tailed tree squirrel of parks and suburban yards. But there are many different kinds of squirrels--over 300 species worldwide, and they live in almost every different kind of environment that we can imagine, from the tropics to the arctic. There are even squirrels that live in some of the harshest, most hot and arid deserts in the world.

Mohave Ground Squirrel, Mohave Desert, Southwestern US

Ground squirrels can be found living and thriving in two of the hottest, driest deserts of the world: the Mohave Desert of southwestern North America; and the Kalahari Desert of southern Africa. In both of these regions, daytime summer air temperatures can reach up to 114 degrees F, with surface soil temperatures as high as a blistering 140 degrees. Needless to say, animals that live in these places must evolve strategies to cope with such extreme conditions. The squirrels of these deserts have indeed developed some ingenious ways to survive.

Cape Ground Squirrels, Kalahari Desert, Southern Africa

One way that desert squirrels survive the heat is through a sort of reverse hibernation called aestivation. Just as ground squirrels and other mammals of cold arctic regions go into hibernation, some ground squirrels of the deserts will put on body fat, go into a burrow, and lower their heart, respiration, and metabolic rate, basically sleeping through some of the hottest months of the year. The Mohave ground squirrel, a rarely-seen ground squirrel of California, will aestivate from mid-summer through the fall, emerging in January or February. During the spring following a drought season, these ground squirrels might even skip mating and reproducing that year, and begin their aestivation as early as April.

Young Mohave Ground Squirrels

Squirrels of the desert also cope with the extreme heat by adjusting the times that they spend looking for food. Cape ground squirrels of the Kalahari desert will usually forage for food during the daytime during the cooler winter months. But in the summer, they will stay underground in their burrows during the hottest parts of the day, emerging to search for food only in the early morning and the late evening. These squirrels also store food in their burrows, so that they will have something to eat during those hottest periods.

When desert squirrels must forage for food in the heat of the midday sun, they can find ways to minimize their discomfort. Round-tailed ground squirrels, another species of the southwestern US, climb into bushes to forage, taking advantage of the shade and minimizing their contact with the hot sand. And the Cape ground squirrels, when they must go out into the daytime sun, use their bushy tails as "umbrellas" to give themselves some shade.

Round-Tailed Ground Squirrel, Southwestern US

It is not surprising that most or all of the squirrels of the deserts are ground squirrels, which live in burrows under the ground surface. Burrows are an extremely important part of the desert squirrels' survival strategy. For example, when measured over a period of a week, the daytime temperature outside reached over 100 degrees F and nighttime temperatures dropped as low as 23 F, but the temperature inside the burrow of the round-tailed ground squirrel stayed between 68-77 degrees F. Often when returning to the burrow after foraging in the hot sun, a squirrel will lie flat on its belly on the cool earth, or like the Mohave ground squirrel, will even dig into the ground, pushing its body through the cool soil, to help dissipate body heat and cool off.

Antelope Squirrel, Southwestern US

Desert ground squirrels have evolved several physical adaptations to cope with the hot and dry conditions in which they live. Some, like the antelope squirrel, are able to withstand higher body temperatures than most animals, even up to 110 degrees F; or, like the Townsend's ground squirrel, have a lower base body temperature, so that it can remain outside in the heat for a longer time before reaching a dangerously high temperature. Many desert ground squirrels have light-colored fur, reflecting the sun's rays, but dark skin pigmentation, which protects them from absorbing excess ultraviolet radiation.

Cape Ground Squirrel

Finally, desert-dwelling squirrels have evolved physical strategies to reduce their need for water. These adaptations include extremely efficient kidneys, reducing water loss through urination; and fewer mucus-producing cells in their lungs, reducing the amount of water lost through respiration. Because of these adaptations, many desert ground squirrels, like the antelope squirrel, can obtain most of the water that they need not through drinking but through the food that they eat.

Round-Tailed Ground Squirrel

Much of the information for this post came from the book Squirrels: The Animal Answer Guide, by Richard W. Thorington Jr. and Katie Ferrell. This book is an excellent source of information and a highly entertaining read for anyone interested in squirrels. If you are interested in this book, you can get a copy by clicking the link below.



1 comment:

  1. Hi there. I live in Toronto, Ontario and earlier this year, my wife, Jean, and I were in Ireland where we came upon the rarely seen Red Squirrel. To us, they actually look somewhat like our American Red squirrels, but boy, do they have long ears! We were shocked to learn that U.K. and Irish Red squirrels are contracting the pox virus from Grey squirrels, and dying. We have far to many Grey squirrels here at our feeders. But up north near Algonquin Park we have seen a few Red squirrels. We feel very lucky to have seen two Red squirrels in Ireland. We have posted some of our pictures and video of our Red squirrel sightings in Ireland, and Canada for anyone interested at: http://frametoframe.ca/photo-essay-red-grey-squirrels-canada-ireland

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