For Alaska’s winter birds, coping with the cold is a matter of survival. How do they do it?

Alaskans find ways to keep warm in the darkest days of winter: puffy coats, bunny boots, flights to Arizona.

But how do the birds of the only Arctic state stay cozy when the mercury dips and the winds howl?

Birds are warm-blooded: Their bodies maintain a constant temperature around 105 degrees. Over time, they’ve evolved some familiar-sounding strategies to crank up their furnaces and keep them stoked.

They shiver. They gorge on food. And they surround their bodies with down.

Somehow it works, from brawny ravens and bald eagles down to the tiny black-capped chickadees and golden-crowned kinglets hopping from branch to wintry branch.

“I think even the most experienced birders I’m friends with, we all marvel at how these small birds can make it through,” said Sulli Gibson, an avid Anchorage birder who in summer guides tours on St. Paul Island in the Pribilofs. “It’s even impressive in the Lower 48 but in Alaska it’s negative 40, negative 50.”

A range of birds spend the winter in Alaska, from large-bodied eagles and ravens to minute songbirds.

Citizen birders logged hundreds of species during last year’s annual Audubon Christmas Bird Count. Anchorage: 39 kinds of birds spotted, including over 1,700 mallards and more than 15,000 Bohemian waxwings. In Bethel, volunteers glimpsed eight kinds of birds including more than 660 ravens.

[New study estimates 3 times as many golden eagles in Alaska than previously believed]

Unalaska Island reported 44 kinds of birds, including 623 black scoters, a large sea duck. The city of Eagle logged nine species, including 51 white-winged crossbills — but zero of the community’s namesake raptor.

For all, finding enough food is crucial and tucking into sheltered spots is key. Alaska’s urban spaces can offer both.

Some birds — the hulking parking lot ravens of Anchorage are one shiny black example — move to the city for winter.

“Alaska is kind of a hungry country. You can’t just expect a caribou or moose to drop dead in your range,” said Rick Sinnott, a former Alaska Department of Fish and Game wildlife biologist. “It’s very common for birds to suck into cities and towns and villages. It’s like a vacuum. They’ll come in because that’s where the dumps are, the dumpsters.”

Ravens start showing up around mid-October in larger numbers, Sinnott said. “All of a sudden, boom! There are 10 times as many or more ravens as in the summer.”

The birds spend the night in the Chugach Mountains near town, maybe huddling under a hemlock canopy for cover. Most cities, including Anchorage and Fairbanks, tend to sit in lower-elevation bowls where cold settles. The mountains can offer warmer air, especially during temperature inversions.

Ravens can fly 5 or 10 miles or more to roost — and commute, Sinnott said.

“They can tuck themselves into these places just about dark and wake up at the crack of dawn to fly into town,” he said.

Parking lots at restaurants, groceries or gas stations provide a steady source of food, whether it’s eggs dropped on the way to the car, half-eaten hamburgers or bags of frozen trash left in the back of a pickup.

[Previously: Anchorage Costco customers say ravens are stealing their groceries in the parking lot]

Ravens have evolved for cold temperatures, said Falk Huettmann, an associate wildlife ecology professor with Institute of Arctic Biology at the University of Alaska Fairbanks.

Their black color steals warmth from the sun. They molt well-insulated feathers as they wear out so they don’t get “leaky” and admit frigid air. Those big beaks don’t lose energy the way the body does. A layer of skin closes over their eyes to guard against the chill.

If one raven finds food, it starts a high-pitched, croaky yelling to others. Pretty soon, there are five more. Then 10. Then dozens.

“They communicate about food items. They basically have a network all over the city when some sort of food is available. They communicate from one to the other to the other,” Huettmann said. “It’s sort of like a relay system. Suddenly you have 50 birds, you don’t know where they came from.”

The birds are so efficient, and urban food so ample, that by midmorning they may take time off to play, Sinnott said.

“Oftentimes it’s a show-off behavior where they’re trying to show off to other ravens,” he said. “They’re just like teenage kids and skateboards.”

Ravens do barrel rolls, drop chunks of ice from 200 feet. Some even go “sledding” down hills on their backs, over and over.

Larger birds have something of a wintertime advantage. But there’s scarce leisure time for little ones.

For chickadees, the tiny and ubiquitous Alaska birds of winter, the business of eating becomes tantamount. The black-capped dynamos stuff themselves with food like seeds.

Fairbanks biologist Susan Sharbaugh discovered that black-capped chickadees gained an additional 10% of their body weight each day. Then they wedge, alone, into tight roosts in birch trees.

“The birds then use that fat to shiver all night, which keeps them warm,” science writer Ned Rozell wrote last year. “The human equivalent would be a 165-pound man who spent a frigid night outside and emerged 15 pounds lighter by the next morning.”

These birds are “Type A personalities,” Gibson said. Their hearts beat 500 times a minute.

But at night, he said, chickadees go into a state approaching torpor — similar to bears — conserving energy by bringing down their heart rates.

Some species huddle together. Treecreepers, bug eaters that scale trunks like mini woodpeckers, “seem to overwinter in some type of ball,” Huettmann said. “They go into old woodpecker holes, five or six together, they stay together and warm each other up.”

Redpolls will fill their cheek pouches so packed with seeds that they are constantly chewing and digesting them, Sinnott said.

“They’re basically still feeding themselves after dark, which is unusual for birds,” he said.

Some birds make use of the white cover on the ground. Bohemian waxwings devour mountain ash berries through the winter, and drink lots of water — or eat snow — to make sure they can digest them all. Ptarmigan and grouse bury themselves in the snow, using it as insulation to stay warm through the night.

Others can be seen in the water, like the hundreds of mallards overwintering on the Chena River in Fairbanks. The ducks put on extra layers of feathers for winter, as do geese. They seek open water where they find it, Gibson said.

“For us, it’s like, cold water is death. You don’t want to fall in,” he said. “But it’s actually crucial for birds to keep their feathers clean. They have to drink water.”

Then there’s the eternal question for winter avian watchers: how do birds keep their feet warm?

For one, they don’t entirely. That’s why they stand on one leg and then the other, tucking their legs up into their bodes for a warm-up.

But birds also evolved with what’s called a “counter-current heat exchange system” in which the blood vessels in their legs sit close together. The chilled blood flowing back to their bodies and hearts is warmed by the blood flowing to their legs, lowering heat loss. And their circulation is so fast that their blood doesn’t stay in their feet long enough to freeze.

Birds are far better adapted to life in the northern winter than most people ever imagine.

A snowy owl named Ghost, a permanent resident at Bird Treatment and Learning Center in Anchorage, makes use of very thick feathers extending from his face to the tip of his snowshoe-esque feet, said Lisa Pajot, a biologist and Bird TLC volunteer. Ghost can fluff up so much his eyes are barely visible.

“To me, it’s always impressive. OK, it’s 20 below but the snowy owl makes it look like it’s 30 degrees,” Pajot said. “He’s completely at ease.”