Squirrels climb down trees headfirst by turning their ankles backwards
Watch a tree squirrel race down a trunk face-first and you are seeing a rare trick among mammals. It rotates its ankles 180 degrees so the hind claws point backward and hook the bark. Its name is a joke of sorts too: the Greek original means shade tail, after the bushy plume many species carry.
Squirrels form the family Sciuridae, about 285 species in 58 genera, spanning tree squirrels, flying squirrels and ground dwellers such as chipmunks, marmots and prairie dogs. They range from pygmy squirrels of 12 to 26 grams to Bhutan's giant flying squirrel, which can stretch 1.27 metres including the tail, and some marmots top 8 kilograms. Native to the Americas, Eurasia and Africa, they were brought to Australia by people. The oldest fossil, Hesperopetes, lived 40 to 35 million years ago and resembled a flying squirrel, and early lineages hint at a North American origin.
English squirrel, first recorded in 1327, came through Anglo-Norman and Old French from Latin sciurus and Greek skiouros, built from words for shade and tail. It displaced Old English ācweorna, whose relatives survive in German Eichhörnchen and Dutch eekhoorn. The tail earns its keep: it balances leaps, sheds heat when more blood is pumped through it, and when curled up the back it can hide the telltale outline of a small mammal from predators behind.
Unable to digest cellulose, squirrels depend on nuts, seeds, fungi and buds, and many will take insects, eggs or small animals when hungry. Early spring is the leanest season in temperate areas, since buried nuts are sprouting and new food has not appeared. In humid subtropical forests, where buried stores rot, some squirrels hang nuts or mushrooms on branches instead; dropped or forgotten nuts help trees such as Cyclobalanopsis spread.
Young are born naked, blind and toothless after three to six weeks of gestation, and wild adults live 5 to 10 years. Squirrels adapt readily to cities; after being nearly wiped out in New York during the Industrial Revolution, they were reintroduced to remind residents of nature. On hot days they sploot, stretching belly-down on cool surfaces.
Source: Squirrel
