Animals deal with winter cold in a variety of ways. Bears tuck in to hibernate in a warm winter den. Moose switch from eating moist leaves to a drier diet of woody stems, branches and bark. And many birds simply fly south to warmer climates.
Many, but certainly not all birds that is, as anyone with a feeder filled with suet, peanut butter or black-oil sunflower seeds could attest to.
“The number of birds that stay year-round is pretty low, but the species that do stay seem to do pretty well for themselves,” said Todd Eskelin, a biological technician at the Kenai National Wildlife Refuge.
Eskelin said “it really is amazing” how small birds — such as chickadees, redpolls and nuthatches — can survive months of winter weather and temperatures that may dip below zero for weeks on end.
“Different species have different strategies,” he said.
According to Eskelin, like many species, birds begin preparing for the long winter when the weather is still fairly mild.
“In fall they’ll fatten up, and then live
on that fat through the winter,” he said.
However, unlike bears that bulk up and then though inactivity slowly deplete there fat reserves to near empty, Eskelin said birds stay relatively active — weather permitting — and try to replenish anything they loose as best they can.
“The fat is a reserve. So, when it’s negative-30 and they can’t go out for food at all or are under conditions of limited intake, they can rely on those reserves. Then, when the weather breaks, they’ll go out and try to build those reserves back up,” he said.
According to the Alaska Department of fish and Game’s wildlife notebook series, some species, such as chickadees, can put on as much as eight percent of their body weight in fat each day — the equivalent of 12 pounds of fat on a 150-pound human.
Different species may eat different things to build their fat reserves back up, with some overlap of course, Eskelin said.
Redpolls love birch seed and so may spend their time foraging in the tops of tress, while chickadees frequently search for frozen caterpillars, spiders and other insects. White-winged crossbills tend to stick to a diet of spruce cone seeds, while pine grosbeaks and waxwings may be seen consuming mountain ash berries.
Of course, many species will also frequent feeders, but Eskelin said this is supplemental to the diet of wild birds, rather than the main course.
“They gain by going to feeders, but they aren’t dependent on them. Some recent studies conducted at feeders have indicated that the birds feeding at them were only intaking 25 percent of their daily caloric needs, while 75 percent of their diet still came from feeding naturally,” he said.
Gorging to gain weight isn’t the only trick up the wings of year-round resident birds. Some also have special adaptations to the cold, such as dense plumage which allows them to trap warm air close to their bodies, and Eskelin said some species can also control their own core temperature.
“They can drop their body temperature at night, which produces less heat, and helps them save energy and conserve fat by burning less,” he said.
Since the average core body temperature for many species is between 104 and 111 degrees Fahrenheit, this can mean as much as a 150-degree difference between the air temperature and body temperature of some birds during cold snaps.
According to Eskelin, some birds of feather will also flock together to stay warm.
“Some species, such as chickadees, will overnight together to conserve heat. It’s not that common, but it does occur,” he said.
Once birds find a few choice places to roost, they may frequent them regularly rather than just tucking in where they are at the end of the day.
“It’s not the same place every night, but they tend to have a handful of places that are safe and protected that they return to on a regular basis,” Eskelin said.
Some species, like chickadees, may tuck under dense spruce bows and hunker down tight against the trunk, he said. Some birds also roost in tiny tree cavities, such as the holes left behind by woodpeckers, or may even spend the night under the eaves of houses and barns for protection.
Joseph Robertia can be reached at joseph.robertia@ peninsulaclarion.com.
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