Raleigh has had a fit of cold, snowy (and icy) weather this week. So while I watched this snow-covered Canada Goose (Branta canadensis) swim around an icy lake near my house, I couldn’t help but think “Brrrrr.”

The core temperature of a goose, wrapped in its fluffy down coat, is ~104° Fahrenheit. But what about those feet? They must be freezing!

In a way, they are. The feet of this goose are only ~35°. As warm blood from the body travels to the toes, it transfers heat to the blood making the return trip. By the time the blood reaches the feet, it’s cold – so cold that little heat escapes through those exposed tootsies.

When the blood moves back toward the heart, it gathers heat from blood vessels traveling toe-ward. This process, called countercurrent heat exchange, keeps the goose nice and toasty.