In the cities of North America and England, the eastern gray squirrel is seen more often than any other wild mammal. The gray squirrel is a tree squirrel, but among the more than 250 other kinds of squirrels are flying squirrels and ground squirrels as well. Also included in the squirrel family are the groundhog and other marmots, the prairie dogs, and the chipmunks. All animals in the squirrel family are rodents.

Where squirrels live

Squirrels live on all continents except Australia and Antarctica. Tree squirrels make their homes in forests and parkland. Ground squirrels live in burrows under prairies, deserts, and farm fields. The flying squirrels, which are less common than the other types, live in the trees of North American, Asian, and Malaysian forests.

Physical features

Like rodents in general, squirrels tend to be small animals. The African pygmy squirrels are the smallest, at about 4 inches (10 centimeters) in length. The largest are the giant squirrels of Asia, which can be 36 inches (90 centimeters) long and weigh 6 ¹/₂ pounds (3 kilograms).

Most members of the squirrel family have large eyes, a coat of short fur, and long bushy tails. The flying squirrels have a large membrane, or loose flap of skin, connecting their front and hind legs. Unlike birds or bats, flying squirrels cannot actually fly. But they can glide for long distances when they spread out this membrane. The eyes of the flying squirrels are enlarged so they can gather more light for better night vision.

Like other rodents, all squirrels have four large incisor teeth for gnawing. These teeth continue to grow throughout the life of the animal. Some squirrels, such as the eastern gray squirrel and the chipmunks, have cheek pouches where they can carry food.

Behavior

Some members of the squirrel family are quite agile. The various tree squirrels are especially good at grasping limbs and other vegetation. They make great leaps between branches and cushion a fall by flattening their bodies and spreading their tail fur.

Many squirrels are known for their quick movements. However, they generally do not try to outrun predators. Instead they go for refuge. Tree squirrels climb trees and shelter in tree cavities. Ground squirrels dive into burrows. Flying squirrels avoid danger by spending very little time on the ground. They also avoid being seen because they are active only at night.

Squirrels eat mostly plants, including young shoots, buds, berries, tree bark, and other vegetation. Many eat large quantities of seeds and nuts. They can use their forelimbs as hands to hold food to the mouth. Some will eat insects when they are available, and a few have been known to raid birds' nests for eggs. The tree squirrels bury nuts and acorns in the ground to eat later. Many of these nuts are never found and take root. In this way forgetful squirrels plant oak trees.

Tree squirrels such as the gray squirrel stay active in cold weather. However, many ground squirrels spend the winter in their burrows in a state of inactivity called hibernation. Some ground squirrels of hot desert regions become inactive in summer instead. This behavior is called estivation.

Tree squirrels are active primarily during the day and spend their nights asleep in trees. Most of them build nests of leaves and twigs, usually in the high branches of the tallest trees. Some build temporary nests that may be used for only one night. The animals usually have several different places to which they can go during bad weather or to avoid predators.

Life cycle

Most members of the squirrel family have one or two small litters each year. The females are pregnant for about 38 to 44 days. Gray squirrels give birth to two to three young in each litter, while Eurasian red squirrels may have five to seven. The young are hairless and helpless at birth. They grow hair after about two weeks. Their eyes open after four to five weeks. They leave the nest to be on their own six to eight weeks after birth and are ready to have their own young the following year.

The longest-lived member of the squirrel family may be the eastern gray squirrel. A gray squirrel in the wild reached an age of 12 years. A zoo-kept individual lived for more than 23 years.

Squirrels and humans

Some squirrels are considered to be pests because they eat farm crops. Others, such as the California ground squirrel, carry fleas that transmit plague, a serious disease. But squirrels can be useful to people as well. The Eurasian red squirrel has been hunted for its fur, and the gray squirrel has been hunted for its meat.

Many people in England do not like gray squirrels. They miss the native red squirrels that were driven off by the gray squirrels that were brought over from North America. The English author Beatrix Potter's character Squirrel Nutkin was a red squirrel.