Sciuridae
Squirrels are a diverse group of rodents that are found world wide, except in Australia, southern South America, and some desert areas. There are about 280 species of squirrels in the world. There are three basic body forms that squirrels take: tree squirrels, flying squirrels, and ground squirrels. Flying squirrels are not capable of true flight, instead they have skin that stretches between their limbs that they use to glide between trees. Ground squirrels are generally robust and tend to be well adapted for burrowing. Tree squirrels are adept climbers with large, bushy tails, long ears, and sharp claws. Squirrels range in size from pygmy squirrels, which are about the size of a mouse, to marmots, which can weigh more than 5 kg.
Most squirrels eat mainly plant foods. Tree squirrels and flying squirrels often eat mainly nuts and seeds, but also include fungi, eggs, insects, and young birds in their diets. Ground squirrels also eat seeds, fruits, and nuts, but often have diets made up of large proportions of grasses and leafy materials as well. Many squirrels store food in their nests or burrows.
Many temperate squirrels hibernate during the winter, taking refuge in nests and burrows and allowing their body temperature to drop to just above freezing. Squirrel species that are found in deserts also practice a form of hibernation, called aestivation. During extreme heat or drought these squirrels enter their burrows and allow their body temperatures to drop and their body functions to slow. These adaptations allow squirrels to live in extreme environments, where food is not always available.
Squirrels are found in all kinds of habitats, from tropical forests to deserts and tundra, and from the tops of trees to underground burrows.