Obviously, some birds migrate away during the winter, but many remain in colder climates. Birds have unique physiological adaptations that make this possible, but other survival strategies also help them manage to live through the winter months.
Some birds change their diets while remaining in northern regions. Red-bellied woodpeckers switch from consuming insects to eating seeds each winter.
Some finches, such as evening grosbeaks and redpolls, move around to find food causing irruptions that are recorded by avid birders. Other birds, such as bluebirds, are partial-migrators, pulling out only at the last minute and then traveling only as far as is necessary to locate food.
As mammals, we humans break down food to produce heat, but birds operate a little differently. Birds shiver to generate heat and require large amounts of fat to fuel their shivering. The average body temperature of a bird is 107 degrees Fahrenheit so they need a lot of fat to maintain their body temperature! Suet and black oiler sunflower seeds are great sources of fat and something we humans can provide to help the birds.
Some birds add an extra layer of fat to help provide additional insulation and fuel their bodies for shivering. Blue Jays are an example of birds that do this.
Down is known as a fantastic insulator—you might even own a down coat or down bedding that you choose when the weather turns cold. Many birds grow extra down feathers each winter to help them survive. Birds can slightly fluff these feathers to form air pockets which trap body heat and become little down jackets that help insulate them. From summer to winter, a goldfinch will add about one-third more feathers, all of which are down. During the late summer months, goldfinches require higher protein to be able to produce these feathers and you can see them actively devouring insects as a source of that protein.
Some birds, such as owls and ptarmigans, grow insulating feathers on their feet and toes. The numerous feathers on the bottom of the ptarmigans’ feet also help keep them running across the top of the snow, much like snowshoes. Ruffled grouse grow pectinations, or fleshy nubs, on their feet each winter that perform a similar function. These nubs fall off each spring.
Other birds run around barefooting across the snowy landscape. Their feet don’t freeze due to a counter-current blood flow that goes up and down their legs. Warm arterial blood flows from the birds’ bodies to their feed and cool venous blood returns to the body. These blood vessels lie directly next to one another, allowing for a heat exchange that helps to keep the birds’ feet warm. Old-fashioned radiators work using a similar principle.
Some birds, including hummingbirds, doves, and nightjars, enter a state of torpor which is much like a short hibernation. These birds lower their body temperature to conserve heat and precious fat reserves. In torpor, these birds slow their heart-rate and breathing as well as their body temperature, which can drop as much as 20 degrees Fahrenheit. The Common Poorwill is able to remain in torpor for long periods of time—even weeks—until the days lengthen and temperatures rise.
Bluebirds, nuthatches, and chickadees have been observed huddling together in nest boxes or nesting pockets at night to stay warm. Not only are the birds protected from fierce winds and wind chills, temperatures inside these structures have been recorded to be about 10 degrees Fahrenheit warmer than the exterior environment. To prevent rodents from over-wintering, be certain your nest boxes and pockets are clean prior to the change of seasons.
Ruffled Grouse bury themselves in the snow at night to keep warm. To build these burrows, they dive into the snow and continue moving about 15-20 feet from the opening. In addition to helping the grouse stay in an environment that rarely plumets below 20 degrees Fahrenheit, the burrows provide protection from predators.
Regardless of the adaptations birds have to survive winter, they always appreciate assistance. As humans, we can help birds survive winter by offering a variety of foods, including thistle, suet, peanuts, and black oiler sunflower seeds throughout the winter months. We can provide clean nest boxes and roosting pockets, orienting the opening away from the prevailing winds. We can make a difference!
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