Gray squirrels climb down trees head-first by reversing their hind feet
Few mammals can run down a tree trunk head-first, but the eastern gray squirrel manages it by swivelling its hind feet so the claws point backward and hook into the bark. That agile acrobat is also North America's great forest planter, and in Britain an invader that has pushed out most native red squirrels.
Native to the eastern and midwestern United States and southern parts of central Canada, the species was once astonishingly abundant in the Midwest. Hunting and forest clearing cut numbers so sharply that by 1900 it had nearly disappeared from Illinois. Fossils show it at least 18 times in the North American Pleistocene record, including bones from a South Carolina swamp site around 19,000 years old.
People then carried it far beyond home. It arrived on Vancouver Island in 1966 and now threatens the local red squirrel there; in Britain it has largely displaced the red squirrel, and it competes with reds in Ireland. Australia's introduced population died out by 1973. Since 2016 the European Union has banned importing, breeding, selling or releasing it.
The genus name comes from Greek words for shadow and tail, picturing a squirrel sheltering under its own bushy tail, while carolinensis honours the Carolinas, where it was first recorded. Black squirrels are a colour form caused by a mutation in the MC1R gene and dominate parts of southeastern Canada; at minus 10 degrees Celsius they lose 18 percent less heat than gray ones. Adults weigh 400 to 600 grams, and males and females look alike.
Nests called dreys, balls of leaves and twigs 30 to 60 centimetres across lined with moss and feathers, sit in tree forks, though attics also serve, with a gnawing habit that can make them fire hazards. Squirrels do not hibernate. A female about to enter heat can draw up to 34 males from as far as 500 metres. Only one kit in four survives its first year, though captive squirrels can reach 20.
Source: Eastern gray squirrel
