How do birds stay warm and handle extremely cold temperatures? Discover the survival superpowers of
birds that brave wintry weather.
Brian Zwiebel
It’s a freezing, blustery day in the dead of winter, but your backyard is alive. Blue jays squawk, northern cardinals perch on snowy branches, American robins dine on berries, nuthatches search for insects in leafless trees, and house finches sip from the heated birdbath. Meet your “resident” birds, hardy souls that have forgone long-distance migration in favor of staying put or migrating short distances.
There are different pathways to winter survival that developed from how birds evolved and what made sense for them, says Mark Faherty, science coordinator for Mass Audubon Cape Cod. “Some evolved to deal with freezing cold nights, while others put all their energy into flying to Central and South America.”
To avoid predators, some residents travel in mixed-species flocks. To keep warm, they fluff their feathers to create insulating air pockets, shiver to generate heat, shelter in dense vegetation, and spend the night in tree cavities and nest boxes, sometimes huddling in small groups.
Food is key to counteract heat loss and maintain body temperature. Some residents migrate short distances to find something to eat. Others cache extra food for later. Many alter their diets to adapt to what’s available. “A resident bird in winter has to fatten up every night as if it were preparing for a mini-migration,” Mark says.
Here’s how some resident birds get through the coldest part of the year.
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Brian Zwiebel
Robins Transition from Insects to Fruit
Cold weather signals to American robins that it’s time to transition from a mixed diet that includes insects to one more focused on fruits and berries. Flocks of up to 50 robins might descend on American holly shrubs or crabapple trees, gorge, then move on. Help these birds by planting berry bushes and offering mealworms, raisins and apple slices.
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nieudacza/Getty Images
Corvids Consume a Diverse Diet
It’s only natural that the loud caws and croaks of resident jays, crows, ravens and black-billed magpies piercing the winter quiet would match their impressive size, appetite and intellect. Corvids feed and roost together, communicate the whereabouts of predators and food, and rarely turn up their beaks at nourishment, whether it’s seeds and nuts, carrion or discarded fast food.
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John C. Gill
Cardinals Crack into Hearty Foods
When not ducking into evergreens to escape biting winds, northern cardinals visit feeders where they use their thick, heavy beaks to crush cracked corn and peanuts, and to pry open black oil sunflower seeds. They’ll also forage for fruit and berries, often discarding the pulp in favor of the seeds inside.
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Brian Zwiebel
Woodpeckers Do Proactive Planning
In the fall, woodpeckers excavate holes in tree trunks to roost inside during winter. When it gets cold, they join mixed-species flocks to find seeds and nuts to cache. Their superpower is their ability to chisel into trees, Mark says. “They can get at all kinds of beetle larvae, carpenter ants and wintering forms of insects that other birds can’t get.”
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Richard Day-Daybreak Imagery
Titmice Visit Feeders Frequently
Tufted titmice are a familiar year-round sight in backyards that have feeders full of sunflower and safflower seeds, suet and peanuts. Along with chickadees, which are in the same family, titmice typically cache seeds within 130 feet of the feeder.
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Bryan Reynolds
Clever Caching of Seeds
The ability to move headfirst down tree trunks has its advantages when it comes to finding insects and caching food that other residents can’t locate. Nuthatches will wedge a seed into tree bark, then pry it open with their bill. They’re often seen joining mixed species foraging flocks.
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Mike Matthews
House Finches Eat Strategically
Like a hibachi chef speed-chopping vegetables, a house finch quickly maneuvers a black oil sunflower seed into place with its tongue before slicing it and extracting the kernel with its stout, conical beak. It’s not unusual for large flocks to show up at winter feeders and gorge on this high-fat food. But they’ll also eat Nyjer and millet, and search out weed seeds and berries.
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Danita Delimont/Shutterstock
Anna’s Hummingbirds Power Down
The dainty Anna’s hummingbird is a fierce winter survivalist. It shuts down its metabolism in a state of torpor at night. Upon waking, it takes about 20 minutes to shake off the torpor before searching for spiders in crevices, small flying insects like gnats, and bugs trapped in tree sap. The bird will drink from heated feeders or those that haven’t frozen and find winter-blooming flowers like hellebores and witch hazel.
There’s a reason that birds look bigger during cold weather. David Swanson, a biology professor at the University of South Dakota who has spent 30 years studying how birds handle inclement conditions, says birds assume a heat-conserving posture and fluff their feathers to stay warm in winter. “It’s similar to goose pimples to form an insulation barrier. It’s almost like putting on a coat,” David says.
Changing Blood Flow for Warmth
David also notes that birds can readily change their blood flow to control what parts of the body remain warm. “When it’s hot outside, they flush heat,” he says. “When it’s cold, they restrict blood flow to the skin. They do a good job of reducing heat loss and improving heat capacity.” To assist this strategy, they’ll tuck a foot, or both feet, and their bills under their feathers because these areas are prone to heat loss.
Shivering to Produce Heat
One of a bird’s most powerful tools for staying warm is shivering. “You don’t think of them shivering all winter, but that’s what they’re doing,” David says. “They turn into little heat-producing machines.” Birds perform more of an isometric exercise where antagonistic muscles work together and produce tension, allowing them to generate heat without exposing more body surface area, which would chill.
The science of shivers: The ability to shiver constantly is based at the cellular level. Birds have more mitochondria packed into their cells, which increases the capacity of the cells to produce ATP, an energy-carrying molecule. This allows birds to continue shivering to maintain their temperature despite cold conditions.
Building Bigger Muscles
To further enhance their shivering capacity, David says they “build a bigger furnace and increase the efficiency of the furnace.” His studies indicate that many birds increase the size of their flight muscles by 10% to 15%, which is similar to a change that occurs during migration.
Putting on Extra Fat
“Most songbirds do get fatter in the winter. They store it by the wishbone and on the belly,” David says. Instead of insulative qualities, he says, “it’s just fuel storage.” This allows them to weather prolonged storms when they cannot forage for food. To do this, he says, “it’s essential that they find food.” Some birds, such as chickadees, woodpeckers and nuthatches, cache seeds in the nooks and crannies of tree bark or shrubs. Others rely on feeders.
Necessary Nutrients: It’s rare for birds to feed during a storm event, but having food nearby is beneficial once the bad weather subsides. Depending on the species in your area, look for high-quality sunflower, safflower or Nyjer seeds—and offer suet or peanut butter for high-energy fats.
Roosting and Huddling Together
Another heat-saving strategy is roosting, or at least huddling, together. While cavity-nesting birds find shelter within trees or similar areas, others sit side by side to reduce overall exposure.
Additional reporting by Amy Grisak
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