Although winter hasn't really visited yet we've had enough cold to prompt some questions and concerns from customers regarding how birds survive winter conditions. First, winter conditions here in the upper south are nothing compared to what birds encounter in the northeast. Even chickadees and kinglets, two of the smallest songbirds, survive the cold of Maine where temperatures often remain below zero for extended periods of time. How do they do this? It is a combination of physiology and strategy.
Chickadees are prodigious gatherers of food, hiding, or caching tidbits of food in hundreds of locations with the ability to remember them all for use later. But how can such a small creature stay warm enough to survive even one night at -20 below zero? Chickadees (like most year-round northern birds) endure the winter in their uninsulated legs and feet. Yet their toes remain flexible and functional at all temperatures. Our exposed toes would freeze and literally drop off. Why do they not freeze? Here's where physiology comes in. It's actually a special adaptation that many birds possess. The temperature in their feet is regulated and will cool down to about 30 degrees while maintaining a body core temperature of around 105 degrees.
A chickadees feet are provided with continuous blood flow. The warm arterial blood headed toward their feet from the body runs next to veins of cooled blood returning from the feet to the body. As heat is transferred between the outgoing and incoming veins, the blood returning into the body recovers much of the heat that would be lost flowing out. So, chickadees feet don't freeze and that's because their foot temperature is regulated near the freezing point even as their body temp stays high. Many species of gulls and ducks that spend a lot of time standing on ice do the same thing.
When you see a bird that looks really fat on a cold day it's not because it overindulged at the feeder but has "puffed out" the feathers increasing the insulating properties. Keeping feathers clean is serious business for birds and this is why you will often see more bathing activity at a birdbath in winter than in summer. Clean feathers mean better weather protection, keeping body temps warm, and creating a barrier to rain.
At night, chickadees reduce heat loss by seeking shelter in tree holes or other crevices. By reducing their body temperature—the smaller the difference in temperature between the bird and its environment, the lower the rate of heat loss. Still, the bird may have to shiver all night and burn up most of its fat reserves, which then must be replenished the next day in order to survive the next night.
Much of the information shared in this blog is from nature author, Bernd Heinrich. If you are looking for some fascinating nature information, I would recommend a few of his books, "A year in the Maine Woods", "Mind of the Raven", and "The Homing Instinct".