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Where do chickadees spend winter nights?

Ned Rozell
A ptarmigan's crop - which is a part of the gullet used to store food - can be the size of softball.
JIM LAVRAKAS / Daily News archive 2006
Insulation and energy conservation allow musk ox, which hardly move at all in the winter, to cope with the cold.
BOB HALLINEN / Daily News archive 1994

Black-capped chickadees stuff themselves with enough seeds and frozen insects to survive 18-hour nights during winter's darkest days.

But where?

Susan Sharbaugh, a biologist with the Alaska Bird Observatory, has devoted years trying to figure out how a creature as light as a handful of paperclips survives minus-40 temperatures for weeks - sometimes months.

In her past studies, Sharbaugh found that black-capped chickadees gain 10 percent of their body weight each day by stuffing themselves, and then burn it at night.

Sharbaugh wondered where black-capped chickadees performed their amazing acts of nighttime survival until a company developed a radio transmitter tiny enough to ride on the bird's back. Weighing 0.5 grams, the transmitter is about the size of an M&M, with a whip antenna approximately five inches long. Sharbaugh attaches the transmitter to captured chickadees with two elastic loops that fit over their legs like a climbing harness.

"They ride really nicely," Sharbaugh said. "You can't even tell the transmitter's there."

After she first attached a transmitter to a chickadee at the UAF campus, Sharbaugh watched the bird disappear into the woods.

People had told her about chickadees flying under the eaves of their homes at dusk. Sharbaugh had seen chickadees with bent tails at her feeder in the morning, which suggested they crammed their tiny bodies somewhere to escape the deep cold.

She ventured into the woods that first night with former UAF biologist Tom Hahn - a receiver in an insulated bag with an antenna that resembled a green ping-pong paddle.

Sharbaugh and Hahn followed the beeping signal to a birch tree with a broken top. They returned at twilight the next afternoon to see the chickadee diving into hole on the tree bark the size of a quarter. They had found a roost, a place where the chickadee wedged itself, puffed its feathers, turned its internal thermostat down 15 degrees Fahrenheit, and burned fat all night.

Chickadees couldn't survive without such a sanctuary.

"Finding a roost is just as critical, if not more critical, than finding food," she said. "You have to find a good and an insulated place to spend the night when you're that small."

Since discovering the first roost, she has found the roosts of several other black-capped chickadees. Using diced peanuts as a lure, Sharbaugh recaptures the birds to remove their transmitters, which have a battery life of about three weeks.

All the roosts have been in birch trees, and she has never seen more than one chickadee enter a roost.

Other birds, such as bluebirds, survive by huddling together, but that appears not to be the case for chickadees.

"They're fairly aggressive toward each other," she said. "It would be difficult for them to share a space."

If chickadees around Fairbanks endure long winter nights in birch trees, the nighttime haunts of their northern relatives - the Siberian willow tit of the Russian arctic and the gray-headed chickadee of Alaska's Brooks Range - remain a mystery.

Those tiny birds live in areas without large trees, and may roost in snow, Sharbaugh speculated.

Ned Rozell is a science writer at the Geophysical Institute, University of Alaska Fairbanks. He can be reached at nrozell@gi.alaska.edu. This column first appeared in 2003.


NED ROZELL
ALASKA SCIENCE