Squirrels live on my front lawn, up in the pine trees. I know I have seen many generations of them now, from young juvenile to old and grey. No matter what the age, they always seem to have a ton of energy to bound around my lawn and others, looking for food, creating stashes, and fighting off birds. They seem to find a way to continually thrive. In the winter they don't hibernate; they will stay in their nest so long as they have a stash of food, but even on a snowy day they can be seen always looking for more.
