From Mark Hayes
I've never seen a Groundhog (also known as Woodchuck and Whistle Pig) in a tree. It seemed unconcerned that I was only about 20 feet away. This was in my local county park so they are accustomed to humans. I've seen this Groundhog before as it dove into a nearby hollow tree as I approached. Another first today.
Groundhogs are indeed squirrels, a fact which Ive been surprising everyone with recently since learning that myself a few weeks ago!
The groundhog, or woodchuck, is one of 14 species of marmots, a subgroup of the squirrel family. One of the largest members, groundhogs live a feast-or- famine lifestyle: they gorge themselves all summer to build up plentiful reserves of fat, then retreat to their underground burrows to snooze through the winter while drawing their sustenance from body fat. During hibernation, the animal's heart rate plunges, and its body temperature is not much warmer than the temperature inside its burrow. (NatGeo)