Alaska animals survive winter in varying ways

MOST IMPORTANT: Getting enough food to provide the energy needed to stay warm.

December 27, 2010 

FAIRBANKS -- Chickadees cache food early in the winter so when it's bitter cold they don't have to expend energy flying to find it.

Moose and caribou have a circulatory system that warms blood in their legs as it moves back to the heart.

Ptarmigan have a crop the size of a softball they can stuff enough food in to last the night while they roost in the snow.

Musk ox barely move.

Wood frogs freeze.

Whether it's a chickadee that weighs less than half an ounce or a moose that weighs 1,200 pounds, animals have different ways of coping with cold temperatures during Alaska's long, bitter winter.

"How you survive all depends on getting enough food," Susan Sharbaugh, senior scientist at the Alaska Bird Observatory, said. "You can survive really low temperatures as long you have enough energy to stay warm."

For some animals, that means getting enough to eat each day to make it to the next day. For other animals, it's more a matter of conserving energy than consuming it.

"Musk ox don't move hardly at all in the winter," wildlife biologist Steve Arthur at the Alaska Department of Fish and Game in Fairbanks said of the hairy, prehistoric-looking creatures that roam the North Slope and Seward Peninsula.

"They're so well insulated they can get by on next to nothing for food if they have enough body fat going into winter. You see them laying there just covered by snowdrifts in late winter."

Big-bodied animals like musk ox, moose and caribou store up large quantities of fat in the fall because the food they eat during winter -- primarily wood -- doesn't provide much protein or energy.

"Moose tend to be conservative in their movements and go to same places they did the year before," said wildlife biologist Rod Boertje, who has studied the animals for nearly 30 years for the Department of Fish and Game.

Ditto caribou.

"They don't move much if they don't need to," Authur said.

When they do move, they follow in each others' tracks to make travel easier, he said.

Both moose and caribou have the ability to slow their metabolic rate about 25 percent, which enables them to survive on less food, state wildlife biologist Rodney Boertje said.

Moose and caribou also have hollow hair that acts as insulation. A moose's long nose helps keep it warm too.

"They're able to warm up the air with an elaborate nasal passage and not have to draw that cold air into their lungs like we do," Boertje said.

Birds like chickadees, gray jays and ravens cache food early in winter for later on, Sharbaugh said.

"They take food when it's abundant and put it somewhere where they can access it when it's cold," she said. "When you see those birds coming to your feeder in August, September and October, doing a lot of rapid trips, they're taking those seeds back and sticking them under tree bark some place."

That's why chickadees don't come in to bird feeders much when it's 30 and 40 degrees below zero, even though that's when you would think they need the food most.

"They don't want to expend the energy flying that they can use to keep warm," Sharbaugh said.

Chickadees scatter their food caches throughout their home range. Studies done on chickadees in Scandinavia showed that they can use thousands of food caches.

"The cool thing is they can remember where it is," Sharbaugh said.

Chickadees gain 10 percent of their body weight in fat each day, which they then burn while roosting in cavities overnight, Sharbaugh said. That would be the equivalent of a 150-pound person gaining 15 pounds during the day and losing it all overnight.

If a bird runs out of food before it's light enough to search for more, it will die, Sharbaugh said.

"It still amazes me they can survive when it's this cold," Sharbaugh said. "Chickadees have six hours of light maximum to get enough energy for that six hours in addition to those 18 hours that they are sitting in a roost."

Redpolls store food in two little pouches next to their esophagus.

"They jam those full of seeds before they go into roost and burn that overnight," Sharbaugh said. "It's sort of like stoking the (wood) stove before you go to bed at night."

Grouse and ptarmigan do essentially the same thing, stuffing their crops full of twigs, buds and sticks that they then digest while roosting in the snow at night.

"They have the same microfauna as moose that they use to break down woody vegetation with help of microbes," Sharbaugh said. "I've seen ptarmigan with a crop the size of a softball. It's a big bag they fill up with food. Then they burrow under the snow and sit there and digest it. When that's all gone they come out and forage again and go back under the snow."

Both birds and ungulates like moose and caribou also have unique counter-current circulatory systems similar to humans that help conserve heat, biologists said. The arteries in an animal's legs run parallel to veins and heat is exchanged from warm blood passing down the arteries to cold blood being pumped up through the veins from the extremities. That way the animals don't have to expend as much energy warming cold blood.

Wood frogs survive the winter because they have the ability to freeze solid by replacing the water in their cells with glucose produced by their liver. The glucose acts as an antifreeze that protects the cells from freezing and drying out. The frog's organs are then encased in ice when the water pumped from the cells freezes. Nearly 70 percent of the frog's total body water is converted to ice and the frog remains frozen until spring.

"The blood freezes, the heart stops beating, all breathing and muscle movements cease, and the wood frog remains in a virtual state of suspended animation until it thaws," according to the Department of Fish and Game's Wildlife Notebook Series.

Sharbaugh never ceases to be amazed by the adaptations animals have developed to survive the harsh climate in Alaska.

"Whenever you look out there and it's dark, there are birds all over the forest waiting for it to get light again so they can go get some more food," she said. "It's a hard life for those little guys."

Tim Mowry is the outdoors editor of the Fairbanks News-Miner.

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