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Now and then, wild birds will stupefy their fans.
For example, how do birds stay warm in the winter? What miraculous adaptations allow them to survive the freezing temperatures, bitter winds, and long nights?
Another mystery: How do they find food? Cold temperatures freeze the ground, or it’s covered with snow. There are no berries on the vine; nuts have fallen, and insects aren’t buzzing. What do they do to beat the problem of low food supplies?
How do birds manage to not freeze and not starve to death during the cold winter months?
Invariably, nature takes care of its own, and birds have adapted to survive the winter. It’s remarkable how they do it… even courageous.
How do Birds Stay Warm in Winter?
Animals have several strategies they use to stay warm in the winter.
Bears hibernate until spring. Deer grow hair that is thicker, longer, and darker and develop a dense undercoat. Bison in Montana and other northern states develop woolen coats. Some species of frogs appear to die as vital organs freeze solid but then resurrect when the weather warms.
But birds do none of these things. And yet, they don’t succumb to frigid temperatures that had Randy’s mom from A Christmas Story dressing him up like “a tick about to pop.”
So, we must ask, “How do they do it?”
Sleeping Habits
Winter nights are unforgiving. They’re long, dark, and usually below freezing. They’re a significant challenge, and different species of birds have distinct strategies for staying alive until morning.
Woodpeckers, for example, adjust their summer behavior to adapt to winter’s conditions.
Woodpeckers are cavity dwellers and, in the summer, will excavate a hole high in a healthy, solid tree. In winter, though, they’ll find a rotting snag (a dead or dying tree) and hollow out a hole about six feet from the ground.
A woodpecker may use a hole for only a few days. Other times they may use the same hole to roost all winter. And while unusual, more than one woodpecker and of different species may roost together in a found cavity.
Golden-crowned kinglets, Eastern bluebirds, house wrens, chickadees, and sparrows will huddle together to stay warm. Small bunches will congregate in a shrub, pine bush, empty bird house, or on a protected branch during winter nights to share body heat. To minimize exposure, they’ll tuck their heads and feet to keep warm.
The ruffed grouse, and snow buntings and redpolls that remain high in the Arctic, will burrow into the snow. Snow is about 90% trapped air and serves as an effective insulator. These birds, and more like them, dig into the snow with their heads and create roosting caves in which to spend the night.
Torpor
Another adaptation birds use to keep warm during the icy winter nights is torpor.
Body temperature varies by species, but a bird’s body temperature is about 105°F. To maintain this high temperature, a bird needs to use a lot of calories to generate the required energy. And as we know, for birds in the winter, calories can be hard to come by.
To conserve life-supporting energy, most birds can lower their body temperature a few degrees. But birds that experience torpor can significantly lower their metabolic rate and drop their body temperatures as much as 50°F without harm.
As effective as torpor is in conserving energy, it can also be dangerous. A reduced body temperature slows a bird’s reaction time. A slower reaction time means birds in torpor are more vulnerable to predators.
Countercurrent Exchange
I have a pair of boots I wear practically every day from mid-November through March. With a pair of wool socks, they’re the only thing that keep my feet warm when the temperature drops. It’s a good thing I have them… I’m miserable when my feet are cold. Really. Miserable.
Birds don’t experience cold feet. A chickadee’s legs and feet, for example, can be as cold as 30°F. It isn’t until ice crystals form that would a bird feel uncomfortable, but that doesn’t happen often thanks to two adaptations.
First, skinny bird legs don’t have a layer of fat to keep them warm. Instead, special scales that reduce heat loss cover their feet and legs. Second, blood in their feet and legs circulates in a way that conserves body heat.
On its way to a bird’s feet, warm blood from the body flows through arteries that are running alongside veins. At the same time, the veins are carrying cold blood from the feet back toward the body.
In a process called countercurrent exchange, the heat from the warm blood transfers to the cold blood, warming it just enough to prevent frostbite. The cold blood coming back to the body warms in the same way and allows the bird to maintain its core body heat.
Feathers and Shivering
Ask anyone who wears a down coat or sleeps under a fluffy down comforter… feathers can keep you toasty and cozy. Peter Marra, head of the Smithsonian Migratory Bird Center at the National Zoo, explains why:
Birds’ feathers provide remarkable insulation against the cold, and the oil that coats feathers also provides waterproofing, which is important since the only thing worse than being cold, is being cold and wet… A bird’s body heat warms the air between its feathers… [B]irds fluff up in the cold to trap as much air in their feathers as possible. The more trapped air, the warmer the bird.
Shivering in humans is an involuntary twitching of the muscles. It’s what causes you to shake and your teeth to chatter. It’s what happens when a body’s core temperature drops. The rapid expansion and contracting of muscles releases energy in the form of heat.
Birds shiver too, but not in the same way we do. When a bird shivers, it rapidly contracts opposing muscle groups, which doesn’t create the same teeth chattering effect we experience. These contractions release heat but in a way that birds can better retain.
During cold nights, a bird may shiver continuously, depleting nearly all the calories they consumed during the day. During the winter, it’s essential that birds refuel as soon as possible after waking. It’s why you see crowds at your feeders early in the morning, gorging themselves… they’re preparing for the next frosty night.
How do Birds Find Food in Winter?
If birds don’t eat enough calories, then they can’t generate the energy they need to keep warm. It’s why finding food in the winter is an even greater imperative than keeping warm.
To ensure they have enough to eat, some animals and birds hoard food. Animal scientists call the hoarding of food caching. More precisely, caching is a behavior animals exhibit when they find, collect, and store or hide food for later use, either in the short- or long-term.
More than 300 species of mammals, arthropods, and birds practice caching of various types.
Caching: Scatter-Hoarding
Scatter-hoarding is the caching of food in multiple places. The technique protects food resources even if another animal raids one or more hiding places. Still, one can never be too careful, so scatter-hoarding birds move and rearrange their caches to throw off would-be thieves.
The trick is remembering where all the caches are, and scatter-hoarding birds are very good at remembering.
Some can remember not only hundreds or thousands of locations but also what they’ve store in each location. They also know not to cache items too close together, preventing a thief who found one hiding place from finding others nearby. Intelligent corvids can even sort out locations where food is likely to have rotted from those where the food is still edible.
Caching: Larder-Hoarding
Rather than hide their food in multiple locations, some birds build larders. Larders are large, single collections of food. Birds and other animals will sometimes build a larder in the same place where they live.
With larders, it isn’t remembering where it’s located that’s the problem… it’s defending it against bandits. And with no back-up supply, if another animal raids a bird’s larder, the consequences could be devastating.
See also: Offering Ground Feeders in Winter
Non-Caching Birds
Food sources are still available in the winter, although obviously not as abundant as in the summer. Some caterpillars, for example, spend the winter frozen to tree branches and when found, provide a good boost of fat for birds.
Spiders and spider eggs are available as are other bugs that hide under bark, beneath the soil, or under water.
Tree buds, waiting for the warmth of spring, are a good source of nutrients and another food source birds will exploit in the winter.
Carnivorous birds such as ravens will take advantage of other animals’ luck, such as a wolf pack that has killed a deer. While a breeding pair of ravens will defend a found meal during the breeding season, they don’t seem to mind sharing with other ravens that have followed them.
Feeding Birds in Winter
Collectively, we’ve done a lot of harm to our environment… harm that makes it even more difficult for birds to survive the winter. In my mind, we have an obligation to help them out when we can, and winter feeding is an excellent start.
When selecting food for your feeders, look for choices high in protein and fat, especially fat. Per calorie, fat provides the most energy. Peanuts, suet, and mealworms are all excellent choices.
Shelled peanuts have wide appeal, but blue jays especially love peanuts in the shell. You’ll notice them grabbing and going to cache them for later.
Tufted titmice, black-capped and Carolina chickadees, white- and red-breasted nuthatches, and many more birds will eat live (preferred) and dried or roasted mealworms.
Suet also attracts a wide variety of birds, especially woodpeckers. They can’t get enough of it. Any bird food supply store will carry it, but it’s also easy to make your own. Add raisins, nuts, peanut butter, quick oats, sunflower seeds, dried cranberries, mealworms… whatever you know your birds will enjoy.
Then grab some hot cocoa, sit at your window, and enjoy the show… knowing you’ve made a difference.