From an article in the NY Times:
The squirrel is related to 278 species which split off from other rodents about 40 million years ago. It includes chipmunks, marmots, woodchucks (groundhogs) and prairie dogs. Squirrels are found on all continents except for Antarctica and Australia.
Squirrels can leap a span 10 times the length of their body, and can rotate their ankles 180 degrees, which allows them to hold on while climbing, no matter which way theyre facing.
Squirrels can learn by watching others. In their book Squirrels: The Animal Answer Guide, Richard W. Thorington Jr. and Katie Ferrell of the Smithsonian Institution described how a squirrel will often wait on the grass near a crosswalk until people began to cross the street, and then follow them.
These sociable little mammals nest communally as multigenerational, matrilineal clans, and at the end of a hard days forage, they greet each other with a mutual nuzzling of cheek and lip glands that looks decidedly like a kiss.
They have an elaborately veined tail, which helps send warm blood toward the squirrels vital organs in the winter and dissipate excess heat in the summer. A squirrels peripheral vision is as sharp as its focal eyesight, which means it can see whats above and beside it without moving its head. In addition, the squirrel has pale yellow lenses that cut down on glare.
Since they are primarily seed hoarders, they gather acorns and other nuts, assess which are in danger of germinating and using up stored nutrients, remove the offending tree embryos with a few quick slices of their incisors, and then cache the sterilized treasure for later consumption, one seed per inch-deep hole.
After they bury the seed, they return to dig it up, rebury it elsewhere, dig it up again. The squirrels recache to deter theft, in case another squirrel was watching the first few times. Reporting in the journal Animal Behaviour, the Steele team showed that when squirrels are certain that they are being watched, they will actively seek to deceive the would-be thieves. Theyll dig a hole, pretend to push an acorn in, and then cover it over, all the while keeping the prized seed hidden in their mouth. Deceptive caching involves some pretty serious decision making, Dr. Steele said. It meets the criteria of tactical deception, which previously was thought to only occur in primates.