Keeping Warm:

When we lived in the  Rockies at 9,800' elevation we were so remote that I had plenty of time to study the birds and animals. This is a hairy woodpecker that hung around our cabin for many years. When it would get really cold he would cling to the side of a tree in the front of the house and puff up his feathers. He was well fed so he had enough energy to stay warm and he would stay on the side of the tree until the sun came out to warm him up. Perhaps this is where we got  the idea of layering clothes to stay warm in the winter.