By Tina Mitchell
You have to know that a bird loves cold if it willingly migrates to South Park for the winter. Of all of the hawks in the Buteo genus, only the Rough-legged Hawk is so thoroughly linked with cold climates. In North America, Rough-legged Hawks breed primarily on the tundra of the Arctic and winter in open country of southern Canada and the northern United States. Driving U.S. Hwy. 285 through South Park during the cold season, you will likely find them perched on power poles or fence posts, surveying the snowy fields. Ah, just like summer in the Arctic! Their numbers in Colorado can vary quite widely from one winter to the next. During our almost 20 years of traversing South Park several times a month, I don’t think a winter passed without our seeing at least a few. On one memorable trip, we counted a whopping 18!
Rough-legged Hawks exhibit considerable plumage variability. Some birds are very dark (dark morphs) while others are paler with a lot of mottled brown (light morphs). Most birds in North America are light morphs, so let’s focus on them. A male Roughie has a whitish to light brown head, a dark eye-line and a light nape contrasting with a dark brown back dappled with white. This back contrasts with Colorado’s other common and similar-sized hawk of winter, the Red-tailed Hawk. A Red-tail has a brown back marked with a V of white reaching from one shoulder, down the back, and up to the other shoulder (the scapular V). Since you often see just the back of a bird scanning the ground from atop a pole, this distinction is surprisingly easy to make. The Roughie’s breast gleams white heavily marked with brown; his tail looks mostly white with a wide dark band toward the tip (easiest to see when the bird is flying). The female resembles the male, except that she is heavier and her back has more brown, with (usually) less mottling. Both sexes have small beaks and small feet – a good adaptation for life in year-round cold. Also, when soaring, both sexes flash distinctive black patches contrasting with light underwing feathers about one third of the way in from the wingtips. By most reports, Colorado hosts far more male Roughies than females, since females tend not to migrate as far south as the males do.
Roughies primarily eat rodents, although they also take many birds. In the winter, carrion can appear on the menu as well. A bird of open, treeless places, a Roughie hunts primarily on the wing, becoming a nearly tireless aerialist hovering over open habitat. There it outcompetes more perch-dependent raptors such as Red-tailed and Ferruginous Hawks by creating elevated hunting perches out of thin air. Although we typically spot them on sturdy poles or fence posts, Roughies sometimes perch on surprisingly flimsy-looking treetops and shrubs or on less-than-steady power lines; all places other buteos rarely choose, because their smaller feet can grip slimmer perches.
The Rough-legged Hawk’s scientific name is Buteo lagopus. Buteo arises from the Latin term for a kind of hawk; the species name (lagopus) derives from Greek for “hare’s foot” (lagus, hare; pous, foot). This name refers to the feathering that reaches all the way down the legs to the tops of the toes, recalling a rabbit’s foot – another good adaptation for staying warm in constant cold. (Only two other raptor species have such feathered legs: Ferruginous Hawk and Golden Eagle.) The common name “rough-legged” describes this feature as well, while “hawk” comes from the Anglo-Saxon word hafoc, their name for these types of bird.
The presence of Rough-legged Hawks in Colorado can be anticipated with surprising regularity, rarely before November or after early April. Unlike many other migrating raptors, their southern migration responds to predictably decreasing daylight hours, rather than any particular weather events or frozen water. Once the days get too short in the Arctic, daylight runs out before Roughies can find sufficient food. As the daylight period lengthens in early spring, they head back to the comforts of the Arctic. (Comfort indeed lies in the eye of the beholder.) So from November through early April, check out large birds on poles and wires. Scapular V? A Red-tail. A mottled-looking back? A Roughie. It can be a great way to pass the time on a long drive. But beware of this non-electronic form of distracted driving!
After a quarter-century in Colorado, Tina and her family recently migrated to Southern California, where she’ll spend the next quarter-century trying to remember that the mountains lie to the east.