Feathered invaders make a stop in Juneau

Posted: Sunday, March 02, 2008

Thousands of redpolls - tiny northern finches - descended on Juneau in recent weeks.

Courtesy Of Mark Henspetert
Courtesy Of Mark Henspetert

It's a bird phenomenon known as an irruption, and chirping, twittering flocks of 100 to 200 redpolls are cleaning out bird feeders, picking at alder cones and gleaning seeds from the tattered remnants of last year's vegetation.

At first glance it's the numbers that seem impressive, but a close looks reveals that the chickadee-size birds themselves are quite striking.

Males and females sport a bright red cap and a contrasting black chin, and mature males have a colorful red wash on the breast. Their scientific name comes from the Latin word for "flame."

"It seems to be an incredible year," said Bob Armstrong, a biologist and author of several natural history books, including the Guide to the Birds of Alaska. "I've noticed them all over. Out at the glacier there was a flock of about a hundred feeding on alder. Out on the wetlands they were on the ground, feeding on sedge and grass seeds that have accumulated over the winter."

Laurie Ferguson Craig works at the Mendenhall Glacier Visitor Center and said flocks of 150 to 200 redpolls have been frequenting the area.

"When they descend on a tree it's like all the leaves have popped out ... and when they take off it's like it's instantly defoliated," she said.

Redpolls are highly social and move in tight, chattering flocks, using flight and contact calls to keep track of one another. They're also fairly tame and will allow close approach and observation.

These northern birds nest in Alaska and northern Canada. They are considered nonmigratory and winter in Alaska if food is available.

An irruption of birds is different than migration, explained Susan Sharbaugh, senior scientist at the Alaska Bird Observatory in Fairbanks.

"It's not like robins moving south for the winter," she said. "These birds are moving around the state, from food source to food source. It's food-driven."

Sharbaugh said redpolls belong to a subset of finches called cardueline finches, a group of northern-adapted birds that also includes pine grosbeaks, pine siskins and crossbills.

"They have a couple of unique things that set them apart, and one is their movements," she said. "It's more east to west than north to south. They're birch and alder seed specialists, especially the crossbills, and they search the boreal forest looking for cone crops."

Redpolls can survive colder temperatures than any other songbird, according to The Audubon Society Encyclopedia of North American Birds. One adaptation that helps is their modified esophagus, enlargements in the tube that carries food from the mouth to the stomach. Sharbaugh described this enlargement as two small sacks at the back of the bird's throat where they can shunt food.

"They fill those up during the day, so they have these two little sacks of food on their shoulders, essentially, and they can process that food all through the night in their roosts," she said.

In addition to stoking their internal fires throughout the night, Armstrong said they will also burrow into snow on cold nights for added insulation.

"That's probably mandatory up north," he said. "They're very common in the winter in Fairbanks."

A close look at a flock of redpolls reveals variety. There maybe a few juncos, chickadees and pine siskins mixed in, but there are always a few standouts among the redpolls.

Females have a streaked, buffy breast. Males have a wash of red on the breast, and some are particularly colorful. Those are the mature males.

The red comes from carotenoids, natural pigments found in food, the same compounds that give color to flamingo feathers, lobster shells, carrots and salmon meat.

"The red coloration comes from the food they eat, and testosterone is used in the metabolic process to convert those pigments to the plumage," said Sharbaugh. "So females, they have a little bit of testosterone, and will have some red, but nothing like a highly testosterone male. Younger males - immature males and more subordinate males - don't have the testosterone level."

It's tough to say where the visiting redpolls will be nesting in the spring.

"A lot of redpolls push north of the Brooks Range and nest on the Slope," Sharbaugh said, "but we'll have birds nesting here in Fairbanks in April. So those birds could be moving up to the Fairbanks area. They also nest in western Alaska and on the Alaska Peninsula."

Juneau birders see a few redpolls almost every winter, but this is clearly a standout winter to enjoy these approachable little "flame" finches.

• Riley Woodford is a writer with the Alaska Department of Fish and Game. He produces the Sounds Wild radio program and the online magazine Alaska Fish and Wildlife News (www.wildlifenews.alaska.gov).

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