Four Birds That Love Winter
These four species thrive in conditions that send other birds south
Do you feel bad when your favorite birds fly south for the winter? Maybe it’s time to get to know some species that thrive in our North American winters—so much so they actually fly here from points farther north.
Of the more than 800 species of breeding birds that range on the continent, about 600 are migratory—and of these about 500 species migrate to the Neotropics in winter. Of the 100 or so species that remain, some have evolved unique adaptations that allow them to survive a winter’s worth of extreme conditions: cold, wind and difficult foraging. These unusual birds include the:
1. Rough-legged hawk. Each fall, when most migratory birds are leaving Upstate New York for points south, rough-legs are leaving their Arctic breeding grounds for destinations in northern U.S. states and southern Canada.
2. Bohemenian waxwing. This bird (above) breeds in open areas at the edges of Canada’s boreal forests. In winter, the bohemian waxwing wanders in search of areas where fruit and berries persist on trees and shrubs. But it rarely ventures farther south than the Colorado Rockies.
3. Gray-crowned rosy finch. One population of this species (left) breeds in Canada’s western coastal ranges and the Cascade Mountains of Washington State. In autumn, the sparrow-sized birds migrate about 1,000 miles—to end up in eastern Wyoming. They spend the winter on wind-whipped mountain slopes, typically at an elevation where humans are prone to contract altitude sickness. They roost at night in narrow cracks in rocky cliffs, then sally out by day to forage for wind-blown wildflower seeds.
4. Spectacled eider. This three-pound sea duck nests in summer in coastal areas in Siberia and on Alaska’s North Slope. It spends winter in the middle of the Bering Sea—specifically in “leads,” or narrow channels, in the sea ice. This means the bird’s legs and is immersed in 29-degree-F seawater 24 hours a day, 7 days a week, while air temperatures hover in the teens with winds gusting from 35 up to 60 miles per hour.
Birds of mystery: Perhaps because the birds spend their whole lives in extreme environments, rough-legged hawks, spectacled eiders, rosy finches and other cold-weather-loving species haven’t been studied as much as some other migratory species. “It’s just plain difficult for biologists to get up to Alaska and northern Canada and then get around in the field,” says David Arsenault, director of the Sierra Nevada Avian Center in California.
Arsenault for example, is one of the few people who has conducted major research on rough-legged hawks (left). In the late 1990s, he studied the birds on one of their wintering grounds, in Montana, where the temperatures often hover at zero degrees or colder in winter. He discovered several ways they seem to have evolved adaptations for thriving in extreme habitats:
* Female rough-legged hawks tend to winter farther north than males. To the south, the trend reverses, and Arsenault thinks the reason may be simple physiology: Female rough-legs are, on average, bigger and heavier than males, and larger size means a smaller surface-to-volume ratio, bringing improved ability to withstand cold temperatures. “Being bigger, they can also fast for a longer time and tolerate the cold if a big storm comes through,” he says.
* Though hawks generally are solitary (not sociable) birds, Arsenault found that the rough-legs in Montana gathered in communal roosts at night, in some cases as many as several hundred birds in one grove of trees. Apparently, the advantages of a sheltered sleeping spot outweigh the natural inclination to lead a loner’s life.
* Rough-legs’ ability to hover when they hunt gives them an advantage in the snow, Arsenault believes. Hover-ability means the hawks can hunt anywhere in treeless wide-open spaces. They’re not confined to hunting where there are trees or telephone poles that provide perching posts to scan for prey.
* Likewise, evolution has finely tuned spectacled eiders to thrive in frigid conditions. To get a meal, these birds (left) must dive exceptionally deep compared to other ducks—as deep as 230 feet down to the seafloor, where they snag clams or other benthic invertebrates. To avoid being caught under the ice and drowned, researchers believe that they may dive only during daylight hours when sunlight can show where open water lies.
Adapted from "Finding Comfort in the Cold" by Cynthia Berger, National Wildlife, February/March 2006.