How Birds Get Through the Winter

Learn about the behaviors and physiological adaptations that birds use to combat cold weather.

January 24, 2021
Ivan Phillipsen

The Problem with Winter

In regions where winters are rough, survival during this season is a major challenge for birds and other animals. It’s when many populations suffer their highest mortalities.

There are three big reasons why winter is a problem for birds. These are more or less the same things that make life hard for humans in winter.

First and most obvious is the cold. As warm-blooded beasts, birds must maintain high body temperatures within a narrow range. The colder their surrounding environment, the more body heat they lose to it. For a bird to counteract this heat loss, it has to eat more food to fuel its metabolism.

But for many birds, food is in short supply in winter. That’s the second reason that winter is a problem. Birds need a lot more food to maintain their body temperatures at the same time of year when food is at its scarcest. Compared to spring and summer, green vegetation is limited and so are the insects that birds eat. The landscape is relatively barren.

The third major reason that winter is hard is that the days are short. This is most dramatic in the higher latitudes of the north and south, in places like Fairbanks, Alaska or Ushuaia in southernmost Argentina. But the hours of daylight are relatively few, even in less extreme latitudes, like where I live here in Oregon, at about 45 degrees north.

Short days combined with cold temperatures are why plants and invertebrates are hard to come by in winter. And birds, most of them anyway, are diurnal animals. They’re active only during the day.

So putting all this together, we can see the problem clearly: birds need to maintain their warm body temperatures. To do this when it's cold, they have to ramp up their metabolism to generate enough body heat to compensate for the heat they’re losing to the environment. But a higher metabolism requires extra food. Food is in short supply in winter. And because the days are short, birds don’t have many hours of daylight to find what little food there is. On top of all that, winter nights are extra long and extra cold. It’s a challenge for a bird just to survive until the next sunrise.

This is a pretty rough situation. When you think about it, it’s amazing that there are any birds that survive through the winter at high latitudes.

We can divide the ways birds deal with winter into two big categories: behavior and physiology. Birds have both behavioral and physiological adaptations that allow them to deal with the challenges of winter.

Before we look at those adaptations, let’s back up and think about the metabolisms of birds and how they keep their small bodies warm and toasty.

Body Temperature, Metabolism

In everyday language, we say that birds are ‘warm-blooded.’ The technical word for this is endothermic. Endothermic critters like birds, humans, and wombats generate their own internal heat. They maintain their body temperatures within a specific and often narrow range. In contrast, ectotherms like reptiles, insects, etc. depend on the surrounding environment to regulate their body temperatures.

How do birds and other endotherms generate their internal heat? Body heat is sort of an accident of metabolism. Bazillions of chemical reactions  chugging away inside the countless cells of a bird’s body release heat as a by-product. Over millions of years of evolution, birds have figured out how to put this by-product to good use. They've co-opted the heat released by metabolism for the purpose of keeping their cells and organs firing on all cylinders, no matter what the outside temperature is. This is beneficial because, in general, a warm-bodied animal can move and think faster than a cold-bodied animal.

Why is that? Well, there’s a relationship between temperature and the speed at which chemical reactions in the body can occur. The warmer it is, the faster the reactions run. At least up to a point. If things get too hot, everything breaks down and goes all to Hell.

But, in general, cellular processes are more efficient at warmer temperatures. These processes include stuff like energy production from food, muscle contraction, nerve signal transmission, repair and healing, and waste elimination.

The lightning quick reflexes of birds and their power of flight demand a lot from the organs and cells, with high-speed chemical reactions able to meet those demands. In fact, biologists hypothesize that the evolution of small body size combined with endothermy—in other words, warm-bloodedness —was a necessary precursor to the evolution of flight in birds.

So being endothermic is a sort of superpower. Not only are birds and other endothermic animals more mobile and quick-thinking compared to most ectotherms, they can also live in a broader range of environments around the world.

The cost of having the superpower of endothermy is that you have to eat and eat and eat some more. You have to keep eating all the time to stoke the fire of your metabolism. Over their long evolutionary history, birds have come to depend on having warm bodies. Their body temperatures vary between 102 to 109 degrees Fahrenheit, which is 39 to 43 degrees celsius.

The protein molecules in birds’ cells and all those chemical reactions have been fine-tuned by natural selection. They work best at body temperature. So the behaviors and physiology of birds are geared toward spending the least amount of energy to keep their body temperatures within a narrow, optimum range.

This is a struggle in cold places, because birds are continually losing body heat to the surrounding environment. There are several ways this happens.

The first is radiation. Radiation is the transfer of heat from a bird’s body to the environment, even when the bird isn’t in contact with anything. This radiation is in the form of infrared energy. In cold environments, heat radiates outward from a bird the way heat blazes out of a wood stove. That’s why birds glow brightly when you look at them with your heat vision goggles. They’re radiating lots of infrared energy, particularly around the beak and face, where they have few insulating feathers.

If a bird is in direct contact with an object, it can also lose heat by another mechanism: conduction. The object might be the ground, plants, water, whatever. If the object is colder than the bird, heat is sort of sucked out of the bird’s body and into the object.The colder the object a bird is touching, the more heat will be conducted out of the bird and into the object.

Heat can also be lost by a third mechanism, which we call convection. This happens when the cold object a bird is in contact with is something that flows, like air or water. Think about wind chill. Wind chill is the effect of heat being whipped away from your body by moving air. That’s convection. Heat loss by convection can be really extreme when a bird is flying around in a cold environment. Air moving over the flying bird’s body removes heat at a rapid pace. Similarly, flowing water removes heat by convection in swimming birds.

So the major ways birds lose heat in winter are radiation, conduction, and convection. These terms come from the physics of thermodynamics. Another physical property that matters a lot in how birds lose heat is their surface-area-to-volume-ratio. This property explains why large birds lose heat more slowly than do small birds.

A small bird like a Common Redpoll has a lot of skin—a lot of surface area—relative to its internal body volume. So it has a high surface-area-

to-volume ratio. Heat is generated internally in a little bird’s body, but that heat has a large surface from which it can radiate outward into the environment. Bigger birds, like Ravens and eagles, have a smaller surface-area-to-volume-ratio. They can hang on to their body heat more easily than little birds.

The physics and math needed to explain this phenomenon properly isn’t something we want to get into. So hopefully we can all understand this intuitively. If nothing else, just remember that little birds lose heat faster than big birds.


If it’s bloody cold and dark and there’s no food around, why don’t you just get the heck out of there? That is, of course, exactly what many birds do. They migrate. Rather than hunker down and suffer through the frigid weather and darkness, they fly en masse toward the equator. These birds spend the winter where conditions are much more agreeable. They return to higher latitudes to breed in summer, when food is plentiful and the days are super long.

However, migration is no walk in the park. It comes with its own risks and tradeoffs. If migration were easy, then we can imagine that all birds would escape winter by migrating. The question of why one bird species migrates while another species doesn’t migrate is an interesting one. The answer isn’t always clear. I already did a whole blog on migration, so check that out if you haven’t already.

The birds we’re focusing on are the ones that don’t flap their way to warmer latitudes in winter. We’re talking about the birds that face their problems, head on; the hardy resident species that live in places where winter is a real slog.

However, some of these resident birds still make seasonal movements. They fly relatively short distances to places where their chances of survival are better. For example, birds that loiter around in the mountains in summer will often retreat to lower elevations when winter rolls around. Or at least during winter storms. We call this altitudinal migration. There are many examples of altitudinal migrants around the world, like Yellow-eyed Juncos in the mountains of Arizona, Gray-hooded Sierra-Finches in Argentina, and Red-billed Choughs in the Himalayas.

Staying Warm

We’ve already talked about how birds generate heat and how they can lose it. Now let’s see how they try to keep their-hard earned body heat. How do bird’s stay warm?

In terms of physiology and anatomy, a bird’s biggest defense against the cold is its plumage. Feathers, especially down feathers, have an amazing ability to insulate against heat loss. Check out the blog, Parts of a Feather and How Feathers Work.

Down feathers have a fluffy structure that creates countless microscopic air pockets close to a bird’s skin. The air is warmed by the bird’s toasty little body and then it stays trapped in the down feathers. Contour feathers on the outside surface of the bird help to deflect wind, rain, and snow away from the layer of insulating down. So contour feathers help reduce heat loss by convection.

Red-throated Ant-tanager (Habia fuscicauda) in Belize. Photo by Phyllis G. Weintraub.

Sometimes birds seem to be fatter or more spherically shaped in winter. It’s just the result of the bird fluffing up its feathers temporarily to create more insulating air spaces in its down. A bird has muscles that raise or lower its contour feathers. This can dramatically and quickly change the overall shape or silhouette of the bird—from sleek and smooth to puffball extreme.

Some birds grow extra down feathers in the fall so they have a thicker coat of insulation when the ice and snow arrive. And birds can pack on some extra fat to use as a source of energy for metabolism. However, birds don’t fatten up quite as much as mammals do as they prep for winter. Small birds, in particular, don’t have the luxury of packing on much more weight. But birds have some other tricks up their sleeves.

Birds that endure cold winters adapt to seasonal changes by acclimatizing. After several days or weeks exposed to dropping temperatures, many birds acclimatize through physiological changes at the cellular level. They become better at ramping up their metabolisms to generate heat in response to chilly weather.

Let’s take an imaginary trip to understand this principal. Say it’s a hot, bright day in June and you’re sitting in your car. You see a flock of little yellow and black birds flitting around, American Goldfinches. On a whim, you decide to sprinkle some sunflower seeds around on the seats of your car, and one of the unsuspecting goldfinches is lured into your car by the seeds. Suddenly the car, you, and the bird all time-travel into the recent past, back 6 months to January of the same year. There’s a gnarly snowstorm swirling around you, the temperature is well below freezing and both of you are immediately chilled to the bone.

American Goldfinch (Spinus tristus). Public domain photo.

Up in a nearby tree, another American Goldfinch is watching you. The bird in the tree looks comfortable and happy. It seems to be tolerating the cold quite well. It turns out that this is the exact same bird that you abducted, but from the past. This January version of the bird is acclimatized to the cold weather. Its physiology had time to adjust to the low temperatures. So it’s not surprising that the January bird is relatively comfortable in the storm. Your little buddy from June is the same individual bird, but it’s going to get hypothermia and die soon because it’s body had no time to acclimatize - and so will you if you didn’t bring a coat. The winter version of the bird, however, can maintain its normal body temp for up to 8 hours, even if the temperature gets down to minus 70 degrees Celsius. Acclimatization makes an enormous difference.

Another physiological response that birds have to the cold is shivering. Their large pectoralis muscles and sometimes their leg muscles can contract to generate extra heat. Properly acclimatized birds can generate more heat by shivering and have more endurance for shivering than birds that aren’t acclimatized.

Now, have you ever seen a duck swimming around in a pond in the winter, surrounded by snow and ice? Or what about a gull standing on a piece of floating ice? How do you think your legs and feet would feel if you were standing knee-deep in freezing water for hours? Or imagine standing barefoot on a slab of ice.

Birds like ducks and gulls have a nifty trick for keeping their bodies warm in these situations, as well as keeping their legs and feet from getting frostbite.

Physiologically, these birds don’t even try to keep their legs and feet at body temperature. These appendages don’t have feathers or muscles. They have basically no insulation. So it would take an enormous amount of energy to keep them warm at the normal 106 degrees Fahrenheit or whatever. Instead, the bird’s feet are allowed to cool down to almost the ambient temperature. They’re kept just warm enough to keep from freezing. This is called regional heterothermy. This is where different regions of the body have dramatically different temperatures. The feet are cold, the body is warm.

A gull standing on a chunk of floating ice has cold feet, but why doesn’t the chilled blood from the bird’s feet end up making the whole bird cold as it flows back into the body? This doesn’t happen because of how the blood vessels are arranged in the gull’s legs. Arteries with hot blood flow from the body to the feet. Running parallel to these arteries, in close contact, are veins with blood returning from the feet. Blood is flowing in opposite directions in these side-by-side blood vessels. Heat from the arteries flows into the veins. So blood flowing to the feet is cooled down at the same time that blood flowing back to the body is warmed up. This is how the bird conserves its heat—most of it stays in the body rather than getting lost through the feet. The technical name for this awesome adaptation is countercurrent heat exchange.

So the anatomical and physiological features of birds that keep them warm include insulating feathers, acclimatization, shivering, and regional heterothermy combined with countercurrent heat exchange.

This brings us back to behavior. What behaviors do birds have for staying warm in winter? Well, one thing they do is exactly what humans do in winter: they seek shelter. When they aren’t out looking for food, birds find relatively warm, protected places to roost. These are microclimates where there’s less wind and where there might be some insulation to retain heat. By choosing the right microclimate, a bird can greatly reduce the amount of calories it needs to burn to stay warm.

Some woodpeckers chisel out cozy roosting cavities in dead trees. Small songbirds will roost in old woodpecker nests or natural cavities in trees. Or they’ll find protected areas deep among the branches of evergreen trees.

Surprisingly, birds rarely make special nests as shelter for the winter. You’d think that would be a good idea. One hypothesis for why that behavior is rare is that by returning to the same conspicuous nest every evening, a small bird might make itself more vulnerable to any watchful predators.

In North America, we do have one bird that makes special winter nests. The Verdin, Auriparus flaviceps, lives in the southwestern desert. This tiny, gray bird has a bright yellow face. Verdins make roosting nests to keep warm in winter. These nests are spherical and lined with vegetation and feathers for insulation. They’re constructed among the branches of desert shrubs. Verdins make totally separate nests for raising their families in the breeding season.

Verdin (Auriparus flaviceps). Photo by Stan.

Grouse and ptarmigan are famous for burrowing into snow for shelter. The Willow Ptarmigan and the Rock Ptarmigan, both in the genus Lagopus, are birds of the far north in Eurasia and North American. These birds are really well-adapted for winter survival. Unlike most birds, like the ducks and gulls we were talking about earlier, ptarmigan have feathers on their feet, including their toes. The genus name Lagopus actually translates as ‘rabbit foot.’ In the winter, when evening comes around, ptarmigans use their feathered feet to dig into the snow. They tunnel through the snow and make a comfy little burrow to spend the night in. If the weather is bad, a ptarmigan will stay in its snow burrow during the day too.

With or without shelter, birds can do a couple other things to keep warm. They tuck their beaks and faces under their scapular feathers to minimize heat loss from the head.

And some birds will cluster together each night, huddling to keep warm. We see this behavior in chickadees, nuthatches, bluebirds, tree swallows, and kinglets, to name a few North American birds. Many other species around the world huddle for warmth, including mousebirds and bee-eaters in Africa and woodswallows and white-eyes in Asia. And of course there are the male Emperor Penguins who huddle tightly in large groups, to survive in the darkness of the Antarctic Winter.

While we’re talking about penguins… those birds are the real masters of surviving in ridiculously cold places. You can read and learn more at the blog about Penguins.

Getting Enough Food

Staying warm by minimizing heat loss is only part of the winter equation for birds. They also have to get enough food to produce that metabolic heat in the first place.

But food is scarce. So getting enough is an enormous challenge, day after day. This is especially true for small birds. Because, remember, small birds lose body heat faster than large birds. They need to eat a lot to make up for the heat that drains away from them rapidly.

One important solution is to store food. Birds of several unrelated families are adept at storing and recovering nutritious food nuggets. This behavior is called caching.

Ever wonder why the chickadees, tits, or nuthatches who visit your feeder grab a seed or two, fly away, then return a few minutes later to do it all over again? Sure, they’re eating some of those seeds. But they’re also tucking some seeds into little nooks and crannies in tree bark. Days or weeks later, they can remember where most, if not all, of these hidden caches are in the forest.

Members of the crow family, such as Clark’s Nutcracker and some jays, also squirrel away hundreds or thousands of seeds for later scarfing. So do some woodpeckers. Shrikes, too, store some of their food for winter consumption. The Great Grey Shrike in Europe caches dead crickets and small mammals by impaling them on thorns.

Cached food can provide 50% or more of a bird’s diet in the depths of winter. But that still leaves a lot of food that must be found by active foraging. For some birds, this isn’t that much harder than in summer. Woodpeckers, for example, can still drill into wood to find insect larvae. Many coastal birds can chow down on their usual fare of marine invertebrates when the tide is out. Ravens fill their bellies with meat from elk and deer killed by wolves. Owls and other raptors hunt small mammals and birds.

But not everyone can rely on a stocked pantry or plentiful prey. Survival is perhaps most precarious for small birds like kinglets. These tiny birds eat insects and other arthropods and rarely, if ever, eat seeds or other plant matter. You may have noticed that bugs are pretty scarce in winter. Amazingly, species like the Golden-crowned Kinglet in America and the Goldcrest of Europe can usually find enough prey to survive the northern winter. These miniature-sized birds glean insect eggs and dormant arthropods like spiders from the small branches and leaves of conifers.

In 1966 there was an epically cold winter with tons of snow.  A study was conducted on the winter survival of Finland’s birds. Researchers from the University of Helsinki conducted a countrywide survey to assess the abundance and mortality rates of different species. To avoid freezing and starvation, many birds just migrated. These birds included species that head south every winter, but also some species that migrate only facultatively. Facultative migrants move to warmer places only when lousy conditions force them to. Examples of facultative migrants in this study included European Goldfinches and Bohemian Waxwings.

You might not be surprised to hear that the birds hit the hardest that winter were the small resident insectivores. Those birds couldn’t fly away, and they couldn’t eat seeds or berries to get by. The Eurasian Treecreeper, Long-tailed Tit, and Goldcrest all suffered heavy losses. The researchers estimated that almost 90% of Finland's Goldcrest population was wiped out.

This research also found that some bird species got through the winter surprisingly well. This was true for all members of the crow family, Corvidae. And the most common seed-eating species fared well too—birds like the Great Tit,  Eurasian Blue Tit, Yellowhammer, and Eurasian Bullfinch.

It turned out that there was a clear explanation for the high survival rates of all these species. They were being fed by humans. Most corvids, tits, and finches survived the terrible winter of 1966 because they could eat their fill of seeds and other treats at backyard bird feeders.

The researchers concluded that food availability was the most important factor for survival. The frigid temperatures alone didn’t wipe out most birds. The ones that died were those that couldn’t find enough food to stoke their metabolisms to keep up with the heat loss.

The diminutive Goldcrests and other insectivorous birds of Finland rarely visit bird feeders. So they didn’t have an endless, artificial supply of food like the seed-eaters. In that extreme winter, the little insectivores just couldn’t find enough food to maintain their body temperatures.

Makes you wonder how your backyard feeder affects the lives of your local avian friends. Does the food we offer in winter make or break the survival of all those sparrows, chickadees, finches, hummingbirds, and jays? Sometimes, yes. Particularly during episodes of severe weather.

Metabolism and Torpor

There’s one more winter survival hack that we haven’t talked about: Hibernation. What about hibernation? We all know about hibernation in mammals. It’s that thing bears and groundhogs do. Besides mammals, many other animals also hibernate to get through the winter, including some reptiles, amphibians, and invertebrates.

But we don’t usually think of birds hibernating. However, many birds do something that’s sort of like short-term hibernation. This incredible physiological ability helps these birds survive when it’s cold and food is limited. It’s called torpor.

This is where a bird at rest can let its metabolism slow down and let its body temperature drop below its normal level. Sometimes well below. Almost all birds that use this strategy do so for only a few hours at a time, typically at night.

A bird in deep torpor isn’t able to respond very quickly, if at all, to external stimuli. It’s not able to switch into “fight or flight” mode when a hungry weasel or house cat comes skulking around.

So deep torpor has the major drawback of making a bird highly vulnerable to predators. Nevertheless, it’s really useful for surviving the night in cold places. It must be, because we observe torpor in many bird species, from several unrelated families. These include hummingbirds, swifts, mousebirds, fairy-wrens, and nightjars. While in a torpid state, with their low body temperatures, these little birds burn a lot fewer calories, so they are more likely to survive through those long, cold winter nights.

There is only one bird species we know of that stays in torpor for an extended time. It’s the Common Poorwill, Phalaenoptilus nuttallii. This is a small, nocturnal, insect-eating member of the nightjar family, Caprimulgidae. It lives across western North America.

Common Poorwill (Phalaenoptilus nuttallii). Public domain photo.

In the winter, a Common Poorwill will find a cozy spot to roost on the ground, tucking itself under a cactus or among some rocks. When the ambient temperature dips below about 50℉ or 10℃, the bird will usually go into torpor. A torpid poorwill’s body temperature can get down to about 40℉. Remember that it’s normal temperature would be around 106℉. And the bird’s oxygen consumption while torpid is only about 10% of what it normally is. If all of this happened in your body, you’d be good and dead.

The poorwill will be in a torpid state on most days for the whole winter. Luckily, the poorwill is amazingly well-camouflaged, with its speckled gray and brown plumage. It blends in really well with a background of rocks and gravel.

People sometimes stumble across these birds in the desert. Native Americans certainly knew about the Common Poorwill and how it behaves in winter. The Hopi Indians called it Hölchoko, which means, “The Sleeping One.”

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