University of Illinois Master Naturalist, Deanna Frautschi reminds us with this image that it is cold out there. Like us, squirrels are active all year long but seek shelter when the winter storms come in tree dens or leaf nests amongst the braches. Studies have shown that squirrels living in dens use less energy in maintaining their body temperature. Like the Master naturalist taking this picture this squirrel doesn't listen to studies but would rather seek out the bird feeder.