Squirrel's Nest

While I was walking around my apartment community today, I noticed a squirrel carrying grass in it mouth onto a Pine tree. It caught my attention and I followed the squirrel to find that it was actually making a nest on the Pine tree. It was kind of a surprise that squirrel's live in/make nests. I never thought about it and I didn't know they make nests on trees like birds. I came home and googled to find some interesting facts about squirrel's over here:-
http://www.squirrels.org/facts.html
Some interesting excerpts:-

Squirrel's belong to the order "Rodentia", with 1650 species, it is the largest group of living mammals.  It also comprises forty percent of all present day mammal species. 

Squirrels chew on tree branches to sharpen and clean their teeth. That's why you may see many small branches on the ground around large trees. They will also chew on power lines for the same reason, this has caused many major power outages throughout the country. 

A female squirrel will choose the strongest male during mating season, but is unlikely to breed with that male again. This is natures way of reducing inbreeding,  and to preserve the species. 

A squirrel will break the shell of a nut with its teeth, then clean the nut by licking it or rubbing on its face before it is buried. This action applies a scent to the nut which helps the squirrel find it later, even under a foot of snow.