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It makes sense that most birds would want to spend the winter somewhere warmer, like the tropics, rather than in the northern regions. Their ability to leave their homes and travel frequently enormous distances twice a year shows how important it is for them to avoid the alternative, which would be to stay and endure bitter cold and howling snowstorms.
Nevertheless, some birds remain and, despite what seems to be overwhelming odds, face the dead of winter. We are amazed and in awe of them because it takes two problems to be solved at once.
The first is that in order to stay active, birds typically need to maintain an elevated body temperature of 105°F. Humans in the north, with our 98. 6°F body temperatures have the same difficulty as others in the winter to remain warm enough to survive; a person walking barefoot in -30°F will attest to this in a matter of seconds.
Finding food is the second challenge to be overcome in the winter. Winter is when most birds’ food supplies are drastically reduced, just when they need food the most to stay warm.
It may be questioned whether birds possess a special winter survival skill. The short answer is: they aren’t. They find numerous solutions to the winter survival conundrum, frequently juggling multiple tasks at once. While some bird species have evolved the evolutionary equivalent of exclusive solutions, most bird species adhere to a straightforward formula: maximize calories consumed and minimize calories expended.
Chickadees brave the winter in their bare, uninsulated legs and feet, just like most year-round northern birds do. Their toes, however, are flexible and useful in any climate, but if ours were that tiny, they would quickly turn into blocks of ice. Don’t they get cold?.
They do. Their feet cool down to near freezing, close to 30°F. Naturally, a bird’s comfort threshold for foot temperature is probably much lower than ours; they wouldn’t experience discomfort until freezing-related damage (ice crystal formation) occurs.
More On Birds and Winter
However, chickadee feet do not freeze because their body temperature is controlled close to freezing and may remain low for the majority of the winter, despite high core body temperatures.
The bird has to generate new heat in the core of its body each time it transfers heat (via blood) to the extremities. Therefore, any chickadee that kept its feet at the same temperature as its body core would quickly lose heat and expend so much energy that it would quickly run out of calories. It is improbable that birds with warm feet could eat quickly enough to stay warm and active.
However, a chickadee’s feet are provided with continuous blood flow. Veins carrying cooled blood returning from the feet to the body are adjacent to the warm arterial blood traveling toward the feet from the body. Much of the heat that would otherwise be lost flowing out of the body is recovered by the blood returning into it as heat is transferred between the outgoing and incoming veins.
By fluffing out their feathers, birds maintain body heat within. In winter, chickadees may appear twice as fat as they do in summer. But they aren’t. All they are doing is puffing up and covering their bodies with more insulation. They lower their body temperature and look for cover in tree holes or other crevices to minimize heat loss at night. The smaller the temperature differential between the bird and its surroundings, the slower the rate of heat loss. To survive the next night, the bird may still need to shiver through the night and burn through the majority of its fat reserves, which will need to be refilled the following day.
For winter survival, the hours of darkness are critical because there are no food calories to replenish those being used. It’s a delicate energy balance, but chickadees and other small winter birds spare the cushion of fat stored during the day by lowering body temperature and decreasing heat production at night.
Food intake is a more important factor in surviving the cold than physiology, which plays a significant role in regulating body temperature. That little chickadee’s internal furnace must be fed and stoked. Observing and tracking chickadees in the winter forest reveals yet another way that they survive the cold.
Chickadees in winter travel in groups. In Maine, I seldom see them alone. They seem to pick at almost anything as they search for food, and when a chickadee finds something to eat, its neighbors catch wind of it and join in. The chickadee winter flock learns from each other and from mistakes made along the way.
In winter, chickadees can still find a wide variety of food sources, including seeds, spiders, their eggs, insects, and their pupae. In the frozen North, invertebrates are rarely observed in the open during the winter, but they do exist and can be found hiding in the ground, beneath bark, or even underwater as they make use of their unique winter survival techniques.
Certain caterpillars freeze solid to tree branches during the winter. Once, I came upon a group of chickadees consuming tiny caterpillars concealed in the evergreen leaves of a cedar tree. Perhaps with the aid of a hint—a blemish stain on the leaf from the caterpillars’ prior munching—some fortunate chickadee had found this cache of frozen caterpillars.
Because of their size, these tiny gnomes of coniferous forests—roughly half the weight of a chickadee—are the pinnacles of warm-blooded winter survival.
Golden-crowned Kinglets, in contrast to chickadees, consume almost only insects, but they are too small to consume some of the larger food items, like a silk-moth cocoon that contains a pupa. Kinglets are not inclined to spend the night in tree holes because, unlike chickadees, they do not build their nests in cavities. Therefore, it appears that Golden-crowned Kinglets face significant challenges at both ends of the energy equation—food intake and heat retention. Nevertheless, at -30°F in the Maine winter woods, I have positively identified them.
There are several theories as to how these kinglets survive the winter, like spending the night in squirrel nests. However, after pursuing them over several winters, I discovered no proof of that I have seen Golden-crowned Kinglets flying in small groups of about six birds, frequently with chickadees, but I have never been able to determine where or how they slept. Every time I saw them last, it was almost completely dark, and then they abruptly disappeared. Could they have disappeared where I had last seen them?.
That turned out to be the case. I once witnessed four kinglets vanish into a pine tree one evening. Later that evening, I cautiously climbed the tree with a flashlight in hand and observed a group of four Golden-crowned Kinglets huddled together on a twig, heads in and tails out. One momentarily protruded its head from the group before retracting it, suggesting that it was staying warm rather than in a state of frigid torpor.
This clever tactic of using each other as heat sources to lessen their own heat loss prevented the birds from having to find or return to a suitable shelter at the end of the day. Rather than traveling alone, they became their own shelter by gathering to huddle together.
Woodpeckers possess the gear and habits necessary to survive the winter on food. In addition to carpenter ants that are hibernating, woodpeckers can obtain wood-boring insect larvae (Hairy and Downy Woodpeckers) thanks to their long, drill-bit bills and capacity to cling to tree trunks and branches (Pileated Woodpeckers) When it comes to providing an overnight shelter, woodpeckers go above and beyond what most other birds can do by building a shelter for themselves.
Although creating a nesting cavity in the spring led to the evolution of shelter-building, their winter dens are very different. Usually in late October or early November, following the first frosts, I discover the first signs of woodpecker overnight shelters. I search the forest floor for collections of light-colored wood chips on top of freshly fallen leaves or on snow, and then I scan overhead.
The excavated roosting cavity is usually in a rotting snag. Nesting holes, on the other hand, are dug in snags with more substantial wood. Winter overnight shelters are typically located at a minimum elevation of 6 feet, which is three times lower than a nesting cavity. Every night, the same woodpeckers visit their same roost hole, which they may use throughout the winter.
But not necessarily. An overnighting hole may only be used for a few days at a time, even though it can be dug in a day or less. Holes already present are also utilized strategically; in one instance, I managed to remove a Downy and a Hairy Woodpecker from the same opening. However, a single woodpecker typically uses a hole at a time. I imagine that the woodpeckers’ food supply and shelters are so reliable that they don’t need to huddle in groups like kinglets.
When necessary, Ruffed Grouse can fly short distances, but they are primarily grounded. But during the winter, they find food in the tops of the trees, where they eat the nutrient-rich buds of aspens, poplars, birches, and hophornbeams, which are about to blossom and turn leaves as soon as the first spring thaws.
Winter is no time of food scarcity for grouse. A grouse perched atop a tree can gather enough buds in roughly fifteen minutes to last it through the night. Similar to this, it can quickly feed again at dawn, producing enough buds in its crop to meet its needs for the duration of the day. In comparison to a kinglet or chickadee that can hardly get enough food to fuel them while they are out foraging continuously all day, thirty minutes is a very small amount of time to feed them.
Although their size would make them seem easy to miss, casual observers in the North Woods rarely spot grouse in the winter. During dusk and dawn, when they fly up into a tree, usually in a group, to quickly scarf down tree buds, bird watchers search for Ruffed Grouse.
Unlike most other birds in the winter woods, they have a large crop, which is a pouch-like extension of the esophagus where food can be stored. This allows them to consume so much food in a matter of minutes. The crop functions similarly to a bag that can be filled and then carry food to the gizzard for digestion at any time of day or night.
After studying our local Ruffed Grouse in western Maine for two winters, I wondered what they did with the remainder of the winter day. Our grouse spent most of the day under the snow when it was fluffy. It would be possible to determine how long they stayed there by counting poop. Based on established snow-den residency periods, I discovered that grouse typically produce three 7 fecal pellets per hour. They generated roughly sixty fecal pellets in a single night, indicating that they might have spent up to sixteen hours in a snow den. That is, they also spent part of the day submerged.
It is commonly known that grouse burrow beneath the snow to protect themselves from the cold and conserve energy. Additionally, grouse have an abundance of food because there are a lot of tree buds for them to nibble on. Instead of finding enough food to survive the winter, their challenge is to avoid being eaten.
In the winter woods, raptors love to prey on grouse. In contrast to their Arctic counterparts, they do not molt into a wintertime mask of white feathers. Ruffed Grouse have an earthy color all year round, so they stand out against white snow from a distance. A goshawk or Great Horned Owl would find it convenient to eat a plump Ruffed Grouse that is perched atop a bare tree. Therefore, the Ruffed Grouse’s snow dens may also be a strategy for lowering predation.
Small perching birds could also stand to gain a great deal from digging in the snow, at least at night. But by and large, they don’t. Redpolls and Snow Buntings that live in the high Arctic may spend a brief night beneath snowdrifts, but no small birds from the northern United States and southern Canada spend the night in the snow.
Given the enormous potential benefits of insulation, the reason they don’t is probably due to the potential expense. On certain bright winter days, warmth melts the top layer of snow, which at night refreezes into a solid crust seal. Thus, a large population of tiny birds could perish in a single night if they were trapped beneath the snow, where they would starve to death and become prey for subnivian mammals. In addition to providing a significant advantage in energy balance over songbirds, the grouse’s size also facilitates its ability to flee from the snow in the event that it becomes necessary.
Crows congregate in thousands each winter to spend the night in communal roosts. They depart on their daily adventures in the morning, but they return in groups at night. These roosts are frequently found in urban areas, where large numbers of crows gather each winter.
Similar to grouse’s snow-denning behavior, this phenomenon is unlikely to have a single explanation. Communal roosts serve as information centers. They are the places where information about where food is, presumably accidentally, shared because crows that don’t know where a corn field or dump is just follow others, which eventually forms a crowd. Crows in large groups not only create a social network for each other to warn one another of impending danger, but they also spread the risk of predator attacks at night.
Ravens are the classic winter bird, thriving in the cold like few other birds. They range into the High Arctic, where they start their nesting season in northern North America in mid-February. Compared to other passerines, their size is advantageous because it slows down the rate of heat loss. Ravens also prey on carnivores like wolves and possibly even humans, and they benefit from one another’s mistakes, sharing knowledge.
Ravens will kill nearly any animal they can capture, but because of their high energy requirements, they must consume the carcasses of large animals that they would never be able to kill in order to survive the winter. The most obvious example of the raven’s carnivorous relationship is its association with wolves. In the Yellowstone ecosystem, for example, ravens arrive at wolf kills minutes after a pack kills an ungulate, like an elk, and feast on the corpse. In other places, a lone raven might find a carcass and head back to the nightly roost, whereupon a swarm of ravens follows the finder to the food source.
Bernd Heinrich is an emeritus professor of biology at the University of Vermont. He is the author of more than 20 books, including Mind of the Raven and Winter World.
Megan Bishop works at the Cornell Lab of Ornithology as a Bartels Science Illustrator.
It’s unlikely that the first lucky raven to find the carcass voluntarily tells other ravens about it. A territorial pair of ravens will ferociously protect a carcass from intruders during the breeding season. But in winter, ravens share food as a crowd. Ravens are able to travel as far north as their providers—wolves, people, and polar bears—by gaining access to large clumped food resources.
Like other corvids (as well as chickadees and nuthatches), ravens store excess food in order to profit from brief food surpluses. Food storage serves as a kind of insurance against the unpredictable future availability of food during the cold, snowy, and starvation seasons. It’s not always the biggest and strongest who survive winter. It just requires understanding the energy input versus output equation, accounting for every possible circumstance, and making sure there are always enough calories left over to survive another day.
How Do Birds Survive Winter?
Birds and winter. Courtesy of Amanda Frank, Unsplash
It’s amazing birds survive the winter when the temperature drops and the ground begins to freeze. By providing food, we can assist our garden birds in gaining much-needed weight, but what about all the birds we are unable to see?
Thousands of species of birds have adapted to live in some of the strangest and most hostile environments on Earth.
storks have hollow bones in their legs to help lift their massive frames off the ground when flying, pelicans have enormous pouches in which to store so much fish, and toucans use their enormous bills to thermoregulate the intense heat of the rainforests. It makes sense that they would have mastered the winter as well.
As is well known, a large number of bird species migrate south or west for the winter in search of warmer climates. Certain species will travel to areas that we might consider to be fairly cold, but in comparison to their potential home, the icy estuaries of East Anglia, UK, are tropical paradises.
However, some birds are referred to as resident birds because they never leave their homes. These birds have exchanged the dangers of migration—like being blown into the ocean by a storm, being hunted by humans or animals on the way, or simply becoming exhausted—for a whole new kind of struggle—the bitter cold—in order to maintain their hard-won territories throughout the year.
While many wild mammals hibernate or grow thicker coats, humans dress more, adjust the thermostat a few degrees, and do other things, resident birds remain in the same outdoor locations, wear the same feathers, and perform daily tasks. Therefore, birds must find solutions to two issues in order to survive winter: finding enough food and staying warm enough.
Since most wild birds naturally have body temperatures around 105˚°F, or 40̚°C, which is considerably higher than ours, any drop in temperature outside seems even colder to them than it does to us.
When you consider that their food supplies are sadly depleted just when they are most needed, the fact that they can endure a single winter, let alone several, is an incredible testament to their tenacity.
Courtesy of Buntysmum, Pixabay
Birds must use a variety of strategies and specialized adaptations to get past these barriers and reach the warmth of spring. To begin with, their feathers serve a much more useful purpose than just being attractive or aiding in flight; they are excellent heat traps.
The majority of a bird’s body is covered in a thick layer of down, a unique type of feather that is highly valued in our pillows, sleeping bags, jackets, and the envy of technical outdoor clothing manufacturers worldwide. Down is found underneath the longer exterior feathers of birds.
Through a process called ptiloerection, birds can “puff these up,” giving the impression that they are larger than they actually are. Instead, they have simply pushed the finer filaments out of their bodies and spread them out, allowing the heat from their interior to escape.
This fluffy barrier captures air pockets near the body, which are then heated by the bird’s internal radiation of warmth, astonishingly holding on to 90% of its core temperature. While down feathers are present in most birds, we are more likely to see them in waterfowl that are raised for our manufactured comfort and warmth because ducks and geese produce large amounts of down to keep their skin warm in freezing water.
Many birds do not have feathers on their legs or feet; instead, they let their feet cool down to nearly the same temperature as the surface they are standing on. By using their tiny feet, birds are able to avoid freezing to death thanks to a process called counter-current exchange.
Instead, birds’ feet have evolved to consist primarily of bones, tendons, and extremely thin-walled blood vessels in the skin that pass incredibly close to each other. This is because any heat lost from the body to the extremities would need to be instantly replaced, which would be impossible to maintain throughout the winter.
The warm blood that leaves the body through the blood vessels that supply the legs and feet merely warms the cool blood that is being transported away from the feet, returning heat to the feet.
Courtesy of Blalonde, Wikimedia Commons
Huddling together is another method that birds, especially smaller ones like long-tailed tits, sparrows, and chickadees, preserve their heat, especially at night.
They group together to form a line or a ball in order to decrease their surface area to volume ratio. Throughout the night, they will compete for position because the ones at the outer edges of the line lose more heat than the ones in the middle.
After spending the majority of the year by themselves or in pairs for breeding, wrens will gather in groups of five or more during the winter to share heat, occasionally reaching sixty.
Many birds, including owls, treecreepers, most of the tit family, woodpeckers, and thrushes, will also seek out cavities in trees, rock faces or quarries, or snags and rotten holes in logs to spend the night in.
It’s possible that you’ve noticed a lot of woodlandbirds disappearing during the winter. This is because they’ve moved farther inside to avoid the chilly winds at the exposed edges, but it’s also more likely that food has survived in the warmer, darker, deeper interior.
If there is no food, then none of the strategies used are meaningful. Planting trees and flowers that can supply those necessary ingredients in the form of seeds, nuts, or even insects in the autumn and through to the winter is crucial because birds require a steady supply of fatty and high-protein foods to survive the winter.
Many birds, including woodpeckers, nuthatches, juncos, and jays, will cache this food during the summer and fall, usually remembering most, if not all, of the hiding spots.
Sharp-billed birds, such as starlings, can still burrow into tree bark to find lifeforms that have buried themselves there to stay warm. Some birds also migrate from summer fruit to winter seeds that are high in oil.
In the winter, birds essentially exist day to day because it is so counterproductive for them to use energy to find food when night falls and temperatures drop even lower. Nevertheless, many of them will shiver to create heat and stay warm, just like humans do.
Almost all of the calories gained during the day are used up by this alone, so the cycle starts over at dawn.
You can make a huge difference in their ability to survive this winter by making sure they have access to plenty of food and fresh water.
The more of us that take that action, the less strain we put on all other “non-garden” birds. As self-serving as it may sound, you will also enjoy some fantastic birdwatching in the winter from the cozy (smug?) comfort of your own house.
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About the author: Our writer and researcher for the Bird Buddy blog is Sim Wood. She is currently remodeling her Slovenian property with her spouse and making do without a plan. She is also proficient in 72 bird species’ calls and songs. Favorite bird: shoebill.
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