I was on my honeymoon last week, and I saw this bird just straight up chilling in this icy water. And I was like, how does this bird not get hypothermia? So I looked it up, and birds have this like, next-level circulation magic called counter-current heat exchange. Like any animal with a circulatory system, birds pump blood from the heart and it travels throughout the body, including down the legs, to the feet, and back to the heart to continue the cycle.
But the problem with this is that birds don’t actually have any insulation in their legs, and so all of that warmth that’s kept in the blood would be lost to the environment in their feet. So what happens in birds is that somewhere between the, like, hips and the upper thigh of the bird, the blood traveling to the feet and the blood traveling from the feet pass very, very close to one another.
They pass so close that the heat going to the feet is actually transferred to the blood coming from the feet. This heat exchange is so effective that while the body of the bird can be of normal body temperature, the feet can be close to freezing. Yeah, so I spent part of my honeymoon learning fun bird facts.