Solving the mystery of why huge flocks of robins are spending winter in Minnesota

It was so cold at the end of December that Auduboners conducting the Christmas bird count in St. Paul looked like Michelin Men, wrapped in many layers of clothing.

My team walked gingerly over the icy trails at Crosby Farm Regional Park along the Mississippi River, hoping to spot a few robins and other songbirds around the seeps and springs. What we got, instead, was a major outbreak of robins, flying in by the dozens to gather on the park's sun-splashed hillside, the one snow-free spot in the landscape. These cold-weather robins hopped on the ground and feverishly tossed leaves aside in their search for small insects, seeds and fallen fruit.

It was amazing to see wave after wave of the big birds flying in. By the end of the morning we'd tallied up 800 robins, a surprising number for a bird that many of us still think of as a harbinger of spring.

Several days later, Minneapolis birder Bruce Fall reported a huge flock of robins at the University of St. Thomas in St. Paul. In just over 35 minutes, he counted something like 2,500 birds flooding in to evergreens to spend the night. And Tom Bell, a birder on Grey Cloud Island in Washington County, counted at least 2,300 robins roosting in a pine plantation not far from his home in 2010.

What's going on, you might ask. What are robins doing here, long after fall migration? And how can they possibly survive our winters?

Part of the story lies in the fact that a few robins have always spent the winter in Minnesota, primarily in the southern part of the state (but also along the North Shore). They've been counted on Christmas bird counts going back to the early part of the past century, and are mentioned in several chronicles of long-ago Minnesota bird life. When conditions turned brutal, those birds either perished or headed southward.

Another part of the story is our warming climate: Temperatures on winter nights simply don't sink as low as they used to, and this makes it easier for birds to survive. Christmas bird count data track very closely to Minnesota's rising nighttime temperatures, with robin numbers beginning to trend upward strongly in the mid-1990s.

"I definitely think climate change is a factor," says Lee Pfannmuller, a biologist with Audubon Minnesota.

Like many other birds, robins can survive cold weather if they find enough food to stoke their inner furnaces. Humans are helping here, as we plant crabapple trees and vines and shrubs that produce fruit. Moving in flocks helps the robins, because flocks are better able to locate food resources than an individual could alone, and flocks can compete more successfully against other fruit-eating species, such as cedar waxwings.

Robins essentially live two separate lives. In the spring and summer they're highly territorial, driving competitors out of their nesting territories and consuming a diet high in insect and worm protein. However, in fall and winter they gather in large flocks and survive on the vitamins and carbohydrates in fruit and berries.

Wintering robins know that sleeping within a thick line of conifers helps them maintain their body heat at night. And they frequent areas with open water, knowing that these provide good forage.

Todd Arnold, a professor in the University of Minnesota's Department of Fisheries, Wildlife and Conservation Biology, says he now regularly see robins out the window of his St. Paul campus office.

"Are robins being lured into making a bad mistake by wintering too far north, but paying the cost during prolonged bad weather?" he wonders. "Or do they survive just as well as migrants, but do better because they get first crack at breeding territories" in the spring?

We don't know, because although robins are the most numerous bird in North America (more than 300 million) and one of the most popular, they're little studied.

Still, we know that the majority of robins are migratory and we can expect those birds to return, beginning in mid-March. But they may find that their counterparts who never left have snapped up the best breeding territories, thereby gaining an edge in the reproduction sweepstakes.

The robins that stay here in winter move around in their search for food and shelter, so don't doubt your eyes if you suddenly encounter a flock of big, orange-chested birds.

St. Paul resident Val Cunningham, who volunteers with the St. Paul Audubon Society and writes about nature for local, regional and national newspapers and magazines, can be reached at valwrites@comcast.net.

If robins are around your area:

• Set out hulled sunflower seeds, peanut hearts and suet bits on a platform feeder.

• Maintain a heated birdbath and refresh it often.

• Plan to plant berry bushes, vines and evergreen trees and shrubs come spring.

• Leave some fallen leaves in autumn as foraging sites.