by Whit Gibbons

October 29, 2006

In spring, it is said, a young man's fancy turns to love. In autumn many people's thoughts turn to . . . squirrels. You may enjoy watching these acrobatic characters in trees or on the ground in woods, parks, and suburban areas. People with bird feeders begin to wonder if they are feeding more gray squirrels than avian visitors. In many states, squirrel hunting season begins in the fall. Whatever your interaction with squirrels, a new book, "Squirrels: The Animal Answer Guide" (2006, Johns Hopkins University Press) by Richard W. Thorington Jr. and Katie Ferrell, will make them more interesting to observe.

The book is not just about the common tree squirrels and flying squirrels everyone is familiar with. It is about the entire family, 278 species, which includes prairie dogs, chipmunks, and groundhogs (aka woodchucks). Like other rodents, members of the squirrel family have two upper and two lower incisors in the front of the mouth. These powerful teeth can gnaw through any type of plant material, including bark, roots, and hard-shelled nuts. In fact, the teeth of squirrels grow throughout their lives, and without the constant gnawing to keep them trimmed back, the front teeth will become longer and longer.

The squirrel family is found on all major land masses worldwide, except Australia, where a variety of marsupials fill their ecological niche, and Madagascar. The authors partition squirrels into three major groups: tree, flying, and ground squirrels. The United States has eight different species of tree squirrels, two of flying squirrels, and a surprisingly high number (56 species) of ground squirrels. South Asia has about the same number of tree and ground squirrels as the United States, but a remarkable three dozen species of flying squirrels.

The largest squirrels in the family are some of the ground-dwelling marmots, which can weigh almost 20 pounds. None of these will be seen jumping from limb to limb of a tree like the agile tree squirrels. A typical gray squirrel weighs about a pound and is about 18 inches long from nose to tail tip. A fox squirrel, a less common species in the Southeast, weighs more than two pounds and is a little bit longer. The impressive giant tree squirrels of southern Asia hold the record with an average weight of about four pounds and a total length of 30 inches. Imagine one of those at your backyard bird feeder. The smallest in the world are the South American pygmy squirrels that weigh less than two ounces.

The book addresses a variety of questions, such as, can they see color? Yes, but only in the manner of someone who is red-green colorblind. That is, squirrels see colors but cannot distinguish between red and green. In enjoying fall colors, a squirrel is most impressed by the yellow leaves. Can squirrels swim? Yes, tree squirrels have been observed swimming across rivers, and a red squirrel in Wisconsin swam more than a mile in Lake Superior from the mainland to an island. Why it chose to swim a mile through the coldest lake in the country remains a mystery. What is the greatest distance a flying squirrel can glide? The maximum recorded distance for North American flying squirrels is 148 feet. The longest documented glides are for a Japanese flying squirrel that traveled 377 feet and a woolly flying squirrel of Pakistan that landed after gliding 492 feet. These are only what have been recorded by ecologists studying the squirrels. The actual record glides are much longer but just haven't yet been measured.

The book also has a section on coat color, which explains that populations of black squirrels, especially in northern regions, are actually gray squirrels. And sections on squirrel reproduction and mating behavior, food and feeding, and general ecology answer numerous questions about this intriguing group of animals.

Of course no book about squirrels would be complete without the obligatory section on how do I keep squirrels away from my . . . house, bird feeder, or garden. In the time-honored tradition of people giving book reports, I advise you to read the book to find the answer to those questions. But in the meantime, learn to enjoy the squirrels.

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