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Originally published Saturday, April 13, 2013 at 8:01 PM

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Familiar robins still harbor mysteries

Rising temperatures and the proliferation of berry bushes in yards across the country have shifted the migratory patterns of the bird everybody thinks they know — but which has actually been studied very little.

Seattle Times science reporter

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The Saturday bird group at Discovery Park hadn’t left the parking lot when they made their first sighting: a pair of robins rooting through leaves and gobbling down waterlogged worms.

As the birders struck out along the park trails, the liquid notes of a robin’s song poured from an alder grove. On a pathway crowded by tall cedars and Douglas firs, robins strode to and fro, punctuating each burst of motion with a quick look around.

From wetlands to meadows and the middle of a road, the ubiquitous birds were taking care of business in every corner of the park on this blustery morning in early April.

“I always talk about robins when I do these walks,” said leader Scott Hoskin. “It’s a bird everybody knows.”

But familiar as they are, robins still harbor mysteries behind their orange breasts and white spectacles.

The species’ ability to thrive alongside humans means it doesn’t get a lot of attention from researchers, who tend to focus on animals in trouble. But those who have studied robins — including several scientists in the Pacific Northwest — marvel at a complex life cycle marked by some of bird-dom’s more dramatic, seasonal about-faces in diet and behavior.

“We take them for granted,” said wildlife biologist Rex Sallabanks, who did his doctoral research on robins in Oregon. “But when you watch them as closely as I did for so long, you really have a much better appreciation for how cool they are.”

Found only in North America, robins are woven into popular culture. But some of the common conceptions about the bird have proved wrong.

Take the species’ reputation as a harbinger of spring, for example.

The notion probably originated in the Northeastern United States, says ornithologist Laura Erickson, who serves as an adviser for Journey North, a citizen science program that has been tracking robins for 20 years.

New England winters used to be too cold for the birds. So it really was a sign of spring when the first robins appeared, fresh from their wintering grounds in the southern U.S.

But today, there are few parts of the country where robins don’t hang around all year. “That first robin of spring — that lovely, romantic notion we all have — is not that easy to distinguish from the last robin of winter anymore,” Erickson said.

The main reason seems to be a warming climate, said Geoff LeBaron, director of the National Audubon Society’s annual Christmas Bird Count. Nearly five decades of data from the surveys show a northward creep in the winter ranges of most North American birds, including robins, for whom the shift is about 200 miles.

Journey North, which enlists individuals and school classes across the country to monitor robins and other ecological markers, received its first report of robins venturing into the northern Arctic in the summer of 2005.

Another factor in robins’ changing habits — and spectacular success — is the spread of ornamental shrubs and trees, like holly and hawthorn, that provide berries throughout the cold months. “Robins have truly benefited from human settlement,” Erickson said. “There are more robins now than when the Pilgrims arrived.”

Christmas counts in New England show a clear upward trend in overwintering robins. But in the Pacific Northwest, robins appear to be less abundant in winter now than during the 1950s and ’60s.

The counts are just a snapshot, and results can be skewed when huge numbers of birds congregate in a survey area, LeBaron said. But if the trend in the Northwest is real, it’s probably because robins across much of British Columbia are no longer forced by frigid weather to take refuge in Washington and Oregon, he said.

“There's no point in flying an extra several hundred miles if you don’t have to.”

But just because robins are here year-round doesn’t mean the birds stalking worms in your yard now are the same ones that were feasting on your cotoneaster bushes in December.

Some robins may never budge from their home turf, said Sallabanks, co-author of the robin entry in “The Birds of North America,” the gold-standard reference. But many of the birds that winter in the Northwest probably return to Canada or higher elevations in spring to breed — though banding data are scarce, he said. At the same time, birds from further south move into Washington and Oregon and set up housekeeping.

Despite changes in their migratory patterns, the robin’s “cheerily, cheer-up, cheer-up” song remains a sign that spring is coming. The birds chatter in the winter, but it’s only when they sense the changing season that males begin to belt out their courtship anthem.

In the Northwest, robins are one of the first birds to sing every year — and often the first to wake in the morning. Scientists blame artificial light for rousing the early birds at increasingly early hours. In many places, robins now start singing at 2:30 a.m.

Some of the fundamental research on robin biology was done in the 1940s by University of Washington zoologist Donald Farner. He used banding data to estimate an average life span of about two years, though some birds live much longer. One banded robin died just shy of its 14th birthday.

In Oregon’s Willamette Valley, Sallabanks, who now works for the Idaho Department of Fish and Game, documented the way robins choose the biggest, most nutritious berries in order to survive the winter.

When the weather is cold, the species becomes gregarious, he explained. They feed in flocks, gorging themselves as night approaches, then gathering in communal roosts. Over two days in 2008, birders in Yakima estimated nearly 260,000 birds were tucking in for the night in a stand of conifers near a golf course. One mangrove swamp in Florida hosted more than 700,000 robins.

But come breeding season, the bonhomie evaporates. Males will attack any rival — even their own reflections in windows.

Robins also alter their eating habits throughout the year far more radically than most birds, Sallabanks said. In winter, they survive almost exclusively on fruit. In spring and summer, they dine on little else than worms and insects.

Even the iconic relationship between robin and worm is not as simple as it appears.

Though the two creatures seem bound together by evolution, worms were not common across much of North America until introduced by settlers, Erickson said.

And is it really true that robins cock their heads to listen for worms before pouncing? Not so much. According to laboratory studies in the 1960s, the birds hunt mainly by sight — which involves a lot of head movement in a species with limited binocular vision. Studies in the 1990s with robins and mealworms found some evidence that the sound of subterranean squirming could be a secondary cue.

Sallabanks can attest to the truth of at least one well-known bit of redbreast folklore: The tale of the drunken robin.

The birds do, indeed, get tipsy from feeding on fermented fruit. “I’ve seen them just staggering around, they were that intoxicated,” he said. “It’s not a myth.”

Sandi Doughton at: 206-464-2491 or sdoughton@seattletimes.com

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