Tree squirrels are the members of the squirrel family (Sciuridae) commonly just referred to as "squirrels". They include more than 100 arboreal species native to all continents except Antarctica and Oceania. They do not form a single natural, or monophyletic, group; they are variously related to others in the squirrel family, including ground squirrels, flying squirrels, marmots, and chipmunks. The defining characteristic used to determine which species of Sciuridae are tree squirrels is dependent on their habitat rather than their physiology. Tree squirrels live mostly among trees, as opposed to those that live in burrows in the ground or among rocks. An exception is the flying squirrel that also makes its home in trees, but has a physiological distinction separating it from its tree squirrel cousins: special flaps of skin called patagia, acting as glider wings, which allow gliding flight. The best-known genus of tree squirrels is Sciurus, which includes the eastern gray squirrel of North America (introduced to Great Britain in the 1870s), the red squirrel of Eurasia, and the North American fox squirrel, among many others. Many tree squirrel species have adapted to human-altered environments such as rural farms, suburban backyards and urban parks.
Classification
Current taxonomy, based on genetic data, splits the tree squirrels into several subfamilies. The following genera of the squirrel family are classified as tree squirrels.
Subfamily Ratufinae Genus Ratufa (Asian giant squirrels) Subfamily Sciurillinae Genus Sciurillus (South American pygmy squirrel) Subfamily Sciurinae Tribe Sciurini (mostly American tree squirrels) Genus Microsciurus (American dwarf squirrels) Genus Rheithrosciurus (Borneo tufted ground squirrel) Genus Sciurus (Eurasian and American tree squirrels) Genus Syntheosciurus (Central American mountain squirrel) Genus Tamiasciurus (American pine squirrels) Subfamily Callosciurinae (Asian tree squirrels) Genus Callosciurus (Oriental tree squirrels, introduced into Europe and South America) Genus Exilisciurus (Asian pygmy squirrels) Genus Funambulus (Asian palm squirrels, introduced into Australia in the 1920s) Genus Glyphotes (sculptor squirrel) Genus Nannosciurus (Asian dwarf squirrel) Genus Prosciurillus (Sulawesi dwarf squirrels) Genus Rubrisciurus (Sulawesi giant squirrel) Genus Sundasciurus (Sunda squirrels) Genus Tamiops (Asian striped squirrels) Subfamily Xerinae Tribe Protoxerini (African tree squirrels) Genus Epixerus (African palm squirrels) Genus Funisciurus (rope squirrels) Genus Heliosciurus (sun squirrels) Genus Myosciurus (African pygmy squirrel) Genus Paraxerus (bush squirrels) Genus Protoxerus (African giant squirrels)
Relationship with humans
Squirrels are generally inquisitive and persistent animals. In residential neighborhoods, they are notorious for circumventing obstacles in order to eat from bird feeders. Although they are expert climbers, and primarily arboreal, some species of squirrels also thrive in urban environments, where they have adapted to humans.
As pets
Squirrels have been kept as pets in Western society at least until the 19th century. Because of their small size and tame nature, they were especially popular with women and the clergy.
As pests
Squirrels are sometimes considered pests because of their propensity to chew on various edible and inedible objects, and their stubborn persistence in trying to get what they want. Their characteristic gnawing trait also aids in maintaining sharp teeth, and because their teeth grow continuously, prevents their over-growth. On occasion, squirrels will chew through plastic and even metal to get to the food. Tree squirrels may bury food in the ground for later retrieval. Squirrels use their keen sense of smell to search for buried food, but can dig numerous holes in the process. This may become an annoyance to gardeners with strict landscape requirements, especially when the garden contains edibles. Homeowners in areas with a heavy squirrel population must be vigilant in keeping attics, basements, and sheds carefully sealed to prevent property damage caused by nesting squirrels. A squirrel nest is called a "drey". Squirrels can create serious fire hazards when they break into buildings. They often treat exposed power cables as tree branches, and gnaw on the electrical insulation. The resulting exposed conductors can short out, causing a fire. For this reason alone, squirrel nests inside buildings cannot be safely ignored. A squirrel nest will also cause problems with noise, excreta, unpleasant odors, and eventual structural damage. Some homeowners resort to more interesting ways of dealing with this problem, such as collecting and placing fur from pets such as domestic cats and dogs in attics. It is thought that this fur would indicate to nesting squirrels that a potential predator roams, and will encourage evacuation. Odoriferous repellents, including mothballs and ammonia, are generally ineffective in expelling squirrels from buildings.
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