Jeremiah Saringe, Canada asked:
I have observed here in Canada that even in the middle of winter you'll see ducks in the lake along the shores swimming by and feeding. What makes them able to swim in very cold water and not freeze their feet that are not covered with feathers or suffer from hypothermia?
Ducks have very little muscle in their feet, mainly tendons. This means that the muscle which makes them move is further from the feet and better insulated, and there's less in the feet to keep warm. Ducks also have a very clever circulation system, where warm blood going down to the feet goes closely past the cold blood coming back from the feet. This is called a counter-current heat exchange as heat is exchanged from the hot blood to the cold, meaning that the birds do not lose too much heat through their feet.