Yet again, another weather forecast looms on the horizon that promises nights well below 0° F. And again I find myself marveling at animals’ ability to survive such extremes, especially the birds who have not migrated to warmer climates. Many of them are so small! Yet nature has this all figured out and birds’ adaptations help the strongest of each species to survive. So how do they do it?
Birds have a number of strategies. One of them is seek sheltered spaces. Birds will find hollows of trees, shrubs, or other crevices so they are protected from the worst of the weather. Many species also huddle together in these spaces! The group cuddle allows them to share body heat. While roosting and trying to stay warm, birds will puff up their feathers – on extremely cold days birds may look fat but they are just trying to keep warm! Fluffing feathers creates air space that heats up and traps warm air around their bodies, kind of like wearing your own down sleeping bag. Birds must keep their feathers clean by preening for maximum heat retention and insulation.
Another strategy to stay warm is to shiver! Just like people do, birds shiver to generate body heat. In addition, many birds go into a state of torpor at night. It’s like a controlled hibernation. Once they are all tucked in, birds will slow their metabolism which lowers their body temperature 10-20 degrees and conserves precious energy. In the morning, the birds warm themselves up and return to feeding to replenish their reserves.
But what about their poor feet? Nature’s got that figured out too. For starters, many birds’ feet are able to get very cold and stay functional, which keeps the birds from expending energy to keep their feet as warm as their bodies. Bird feet can stay near freezing because they are made up of mostly bone and tendon, with little nerve tissue or muscle that could sustain damage (like with humans). In addition, birds have a countercurrent heat exchange system in their feet. In this system, the arteries of warm blood headed to a bird’s feet run right next to the veins returning from the feet with cool blood. The warm blood heats the cool blood returning to the body, allowing the birds’ cores to stay warm without expending extra energy. Many birds will also tuck one leg up against their body or sit down in order to warm their feet. Some will even tuck their bills into their back feathers. Not only does this warm the bill, but it improves breathing efficiency because they are breathing in the warm air near their bodies, not the icy cold air around them.
And while nature does have all this figured out, if you are so inclined, put out extra bird seed on cold days so your feathered friends can replace the calories they lost trying to stay warm.