Unlike many other mammals, squirrels are often quite conspicuous, with their usually diurnal habits (flying species being the nocturnal exception) and tolerance of human presence. In the USA and Canada, particularly the west, squirrels are unusually diverse in form, with a number of different groups represented. North America's squirrels include the marmots (6 species), prairie dogs (4), ground squirrels (21), antelope squirrels (4), chipmunks (22), tree squirrels (8), and flying squirrels (2).
