How can small birds survive our January cold weather?

Dark-eyed junco. Photo Jeff Steele, iNaturalist.

On his recent visit to the Preserve, Jeff Steele photographed some tiny song birds foraging for food and working on keeping warm. How can they survive this bitter cold Wisconsin weather? The short answer is that they use several survival strategies: they eat foods with high fat and caloric content, they shiver to fluff up their feathers, and they stay out of the wind. 

Tree sparrows, for example, change their diet from insects, high protein food available in summer, to seeds, high in oil and fat content. Proteins are needed for growth, none of that in winter, whereas fats provide energy to stay warm. Chickadees also search for dormant insect larvae in the bark of branches. Apparently they eat at least 35% of their body weight to stay alive.

In addition, these tiny birds may grow up to 30% more feathers in winter to insulate them from the cold. They fluff up their insulating downy feathers, which keep warm air trapped beneath the contour feathers against their small bodies, maintaining their body temperature up to 104 F.  They are experts in shivering which helps them retain heat. Chickadees also have a nifty way to prevent heat exchange with other surfaces by restricting circulation of blood in their legs. Finally, during those long cold winter nights, tiny birds can still use another method to stay warm. They enter what is called "torpor", when body temperature drops and they slow down metabolic functions, similar to animals in hibernation.

Staying out of the wind is also important. Seeking protection, our tiny song birds will huddle together in groups, hide under vegetation and tree bark, and even seek out vacant bird houses.