Squirrels, such as the Eastern Gray Squirrel, Sciurus carolinensis, at the right, as well as chipmunks, are rodents, just like mice and rats. They all belong to the order Rodentia. A conspicuous feature uniting squirrels with rats and mice is their teeth. In the front of all rodent mouths, including those of squirrels, there are four chisel-like gnawing-teeth called incisors, two above and two below. Immediately behind the incisors there's a space, and then flattish back teeth appear. These back teeth, or "cheek" teeth, are adapted for grinding. The vast majority of rodents also have four toes on each front foot, and five on each hind foot.
Inside the rodent order, the Squirrel Family is a big one holding not only squirrels, but also chipmunks, ground squirrels, prairie dogs, woodchucks, and marmots. Often the squirrels inhabiting our backyard trees are called "tree squirrels," so as to not confuse them with ground squirrels and flying squirrels. Burt & Grossenheider's A Field Guide to the Mammals recognizes the following North American tree-squirrel species:
Western Gray...Sciurus griseus
Eastern Gray...Sciurus carolinensis
Arizona Gray...Sciurus arizonensis
Eastern Fox....Sciurus niger
Apache Fox.....Sciurus apache
In the eastern U.S. and adjacent Canada the common "park squirrel" is the Eastern Gray Squirrel. In California, western Oregon, and west-central Washington, it's the Western Gray. Other squirrel species are more restricted to wild areas, though some of them have learned to beg from campers and picnickers in parks. The Golden-mantled Squirrel at the right, smaller than most squirrels and with stripes along its sides like a chipmunk, was photographed inside a large tent full of humans attending a camp meeting in California's Sierra Nevada Mountains.
There are even more species of chipmunks than squirrels, and once again most species are Western, and most are found in the mountains.
A Field Guide to the Mammals recognizes the following North American chipmunk species:
Yellow Pine.....Eutamias amoenus
Charleston Mtn..Eutamias palmeri
In most of Eastern North America only the Eastern Chipmunk is found. One difference between tree squirrels and chipmunks is that chipmunks have internal cheek pouches in which they can temporarily store food as they forage on the ground -- using them like pockets -- while tree squirrels don't (but ground squirrels do). Though chipmunks can climb trees, they are more ground-oriented than tree squirrels, typically living in burrows in the ground, especially in rocky areas and among tree roots.
All members of the squirrel family except the flying squirrels are diurnal -- they're active during the day. This is rare among wild mammals! And it's fortunate for us backyard naturalists, for it makes squirrels relatively easy to watch.
You just have to wonder: How come members of the squirrel family are diurnal, while most other mammals are strictly nocturnal, or active during the night? A good guess is that members of this family are so good at escaping predator attacks that they just don't have to slink around in the night. Chipmunks, ground squirrels, prairie dogs, woodchucks, and marmots are seldom seen far from their burrows. But, tree squirrels... well, just watch what they do when the neighbor's dog catches one on the ground! In a flash it'll be back up its tree!
This doesn't mean that squirrels have it easy. Hawks attack them, snakes enter their nests and, in towns, domestic house cats catch enormous numbers of squirrels on the ground by waiting, waiting, waiting until a squirrel wanders along...
One reason squirrels come to the ground is to bury and retrieve food. In the fall you can often see them digging small holes in the ground called caches (pronounces CASH-ez), into which they deposit food, especially nuts and acorns. They may cache thousands of nuts and acorns during a season. On warm days throughout the winter, then, when food is scarce, the squirrel descends to the ground and digs up its treasures. Many nuts and acorns are never retrieved, so they sprout in the spring, and develop into trees. Thus one important job the squirrel does in the ecosystem is to plant trees.
Especially with a pair of binoculars you can see plenty of tree-squirrel behavior -- such as shown at the right, where an Eastern Fox Squirrel is eating a Wood Duck's egg. You might also see them building two kinds of tree-nests. Courtship between males and females is very complex and dramatic, and so is the conflict among males to establish who's top squirrel in the neighborhood. When young emerge, you can watch them foraging with their mother, learning how to eat various foods, and getting into all kinds of mischief. Once you gain a little practice watching them, following them, figuring out what they're doing, and making good notes, you'll be surprised at how much of this wild animal's life cycle you can chronicle!
Jim Conrad has written a story about a tree squirrel called Mistletoe. The story follows Mistletoe throughout an entire year and offers a kind of "insider's view" to what it's like being a squirrel. Though Mistletoe has a number of wild adventures, all of her behavior is what would be expected of a real-life squirrel in similar situations. There are no talking animals here, just a fine story based on real squirrel behavior. This may be a good time to view and copy this story.