By Gail Cleveland
During the winter, if you see a large hawk soaring or hovering over grasslands, chances are you have spotted a Rough-legged Hawk. They are the most common winter soaring hawk of the Genus Buteo and the only one that prefers cold climates all year. It nests in the Arctic, mostly in cliffs in tundra regions north of boreal forests; the entire population migrates south, wintering in southern Canada and the United States with few moving farther south than central US.
The Rough-legged Hawk gets its name from the feathering that extends down the legs to the base of the toes, an adaptation which may be helpful for staying warm in its preferred frigid weather.
Identification would be easy if there weren’t a few Red-Tailed Hawks that do not migrate south for the winter. About the size and shape of a Red-Tail, Rough-legged Hawks appear slightly longer and less rotund in profile when perched on power poles. In this position and in flight, look for a pale head in contrast to the Red-Tail’s dark one. Another telling feature of a perched Rough-legged is the lack of whitish scapulars on folded wings that form a pale V across the bird’s back. This is characteristic of a Red-Tail. Thus, pale head from the front and no pale V on the back are good indicators of a Rough-Legged Hawk.
A pale chest with a bold dark swath across the belly is another sign of an immature or female Rough-Legged. Most of the birds that you will see will be females, which are larger than the males. “The tendency for females to winter farther north than males is consistent with the body-size hypothesis, which states that individuals of the larger sex (females, in this case) are better able to withstand cold temperatures than are individuals of the smallbodied sex” (Birds of Montana by Marks, Hendricks and Casey). In California and Nevada, males outnumber females.
In flight the white or pale tail with a single or several narrow dark bands as well as black patches on the wrists and black wing tips can help in identification. There are light and dark morphs and immature birds, but these general diagnostic tools should be helpful. The number of Rough-legged Hawks in western Montana can vary dramatically year to year and is dependent on their food source. When breeding in the north, they dine on lemmings; here in western Montana, voles become their primary target. Both these rodent populations tend to have wild fluctuations in numbers from year to year. How do these hawks know where the dining will be good? A recent experimental study shows that the vision of many daylight feeding birds extends into the ultraviolet. Voles mark their runways with urine and feces that are visible in ultraviolet light. Consequently, “they probably can assess vole numbers across large areas simply by flying over and looking for scent marks” (Birds of Montana).
The Mission Valley is one of the prime locations to see these beauties from mid-October through mid-April. Thanks to Chad Olson’s research work there from 1994-2000, we know a great deal about the roosting behavior of this winter Buteo. Olson discovered a roost that housed as many as 300 Roughlegged Hawks during peak vole years, making it the largest communal roost known for the species. In the foothills of the Mission Mountains, the roost was warmer and less windy than the grassland foraging grounds. Olson suggested that the roost was used because of this favorable climate. Hawks commuted up to 15 miles from their foraging grounds to roost in this area at night. Because of his discoveries, the Christmas Bird Counts of Rough-legged Hawks in the Ninepipe National Wildlife Refuge count area have been the highest in the state, and in 1998 it boasted an all-time high for the species in any CBC in North America at 253.
Don’t let the winter pass by without a trip to the Mission Valley or the Lower Flathead in order to identify that perched or soaring hawk, that lover of cold climates and small rodents, the stunning Roughlegged Hawk.