How Do Chickadees Survive Winter? Tiny Birds in the Cold

A tiny bird in a deep freeze

The black-capped chickadee weighs only 9–14 g (0.3–0.5 oz), about as much as two US quarters, yet it stays all winter in places where nights can fall to -30 °C (-22 °F) or even -40 °C (-40 °F) in interior Alaska and Canada. Small animals lose heat much faster than large ones because they have more surface area compared with their volume, so for a chickadee every winter night is a test of survival.

A chickadee’s normal body temperature is about 42 °C (108 °F), higher than ours. To keep it up through a long night, the bird must eat enough during the short winter day, sometimes only eight or nine hours of light, to fuel its body until morning.

Feathers: a down jacket that fluffs up

After its late-summer molt, a chickadee wears a fresh, dense coat of feathers. On cold days it fluffs them up, trapping a thick layer of still air next to the skin, which makes it look much rounder and greatly reduces heat loss. That is why chickadees look like round balls of feathers on frosty mornings.

The bird can also tuck its bill into its back feathers and draw one leg up into its belly plumage. Its legs and feet have little fleshy tissue and a special arrangement of blood vessels that cools the blood going to the feet and warms it on the way back, so little heat is lost even when perching on icy branches.

Shivering, fat and nightly hypothermia

Chickadees produce heat by shivering, contracting their large flight muscles rapidly without moving their wings. They can keep shivering for hours, and they burn fat to do it.

Each winter day, a chickadee builds up a layer of fat, roughly a tenth of its body weight, and burns most of it overnight. At night, it also lets its body temperature drop by as much as 10–12 °C (18–22 °F), to around 30 °C (86 °F). This controlled cooling, called regulated hypothermia, lowers the energy it needs to stay alive and can save a significant share of its overnight fuel. In the morning, the bird shivers itself warm again before setting out to feed.

Few birds can do this. Hummingbirds go even further, entering a deep torpor on cold nights, as explained in how do hummingbirds sleep?

Tree holes and sheltered roosts

Chickadees sleep alone, usually in a tree cavity, an old woodpecker hole, a nest box or thick evergreen foliage. A cavity shelters the bird from wind, snow and rain, is several degrees warmer than the open air on a cold night, and hides it from owls. Black-capped chickadees only rarely huddle together, unlike some other small birds.

Choosing a good roost is so important that chickadees may return to the same hole night after night through the winter.

Hidden food and an amazing memory

In autumn, chickadees hide seeds and insects one at a time in bark crevices, under lichen, among conifer needles and in knotholes. A single bird can make thousands of caches in a season, and experiments show that chickadees remember the locations of many of them for days to weeks.

These hidden stores are especially valuable during storms, ice and deep snow, when fresh food is hard to reach. Scientists have found that the hippocampus, the brain region used for spatial memory, is larger in chickadees than in birds that do not store food, and that new nerve cells are added to it most actively in autumn, the main caching season. Chickadees from harsh climates such as Alaska have larger hippocampi and perform better in memory tests than chickadees from milder regions like Kansas, suggesting that tough winters favor better memory.

Winter flocks and bird feeders

In fall, chickadees join small flocks with a strict pecking order, usually a few pairs and some young birds. Flocks defend a winter home range and often include nuthatches, titmice, downy woodpeckers, kinglets and brown creepers. Many eyes spot predators sooner, and flock members share information about food. Their alarm calls are described in why do chickadees say chickadee?

Bird feeders also help. One long-term study in the upper Midwest found that during severe winters with long spells below -18 °C (0 °F), chickadees with access to feeders were about twice as likely to survive as birds without them. Even so, chickadees that visit feeders daily still take most of their food from natural sources, so feeders supplement rather than replace wild food.

How chickadees compare with other winter survivors

Animals have very different strategies for getting through the cold. Many birds migrate, as explained in why do birds migrate?, while some mammals, reptiles and insects hibernate for weeks or months, as listed in our guide to animals that hibernate.

Chickadees do neither. They stay active every day and rely on a nightly drop in temperature rather than true hibernation. Among birds, only the common poorwill of western North America is known to hibernate for weeks at a time. The chickadee’s mix of insulation, shivering, nightly hypothermia, food caching and teamwork is what lets a bird that weighs about as much as two coins endure some of the coldest winters on the continent.