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ROUGH-LEGGED
HAWK |
| The rough-legged hawk is not
the victim of an unfortunate medical condition. It takes its common name
from a feature uncommon among diurnal (active by day) birds of
prey - feathered legs. In this species the front of the legs is feathered
right down to the top of the feet, as though the hawk were wearing precisely
tailored trousers. Probably these feathered leggings help protect the
rough-leg from the bites of rodent prey. The only other day-hunting North
American raptors to exhibit this characteristic are two other rodent hunters
- the ferruginous hawk and the golden eagle (most owls, rodent hunters
supreme, have feathered legs and feathered toes). This attractive hawk is not seen in our area during the spring and summer months. Its breeding grounds stretch from the outer edges of the boreal (northern) forest, where the stunted trees are widely spaced, right up into the treeless tundra. This breeding range is referred to as holarctic, which means it extends in a wide, continuous belt across the lower arctic and subarctic regions of North America, Greenland and Eurasia. In North America the rough-leg nests from the Aleutian Islands and Alaska eastward across arctic and subarctic Canada, including parts of Labrador, Newfoundland and Quebec. Cold weather comes early to these northern reaches. By late August the rough-legged hawk is massing for migration out of its summer home. Although a few birds apparently stay on their home territories if there is enough food, the majority migrate to southern Canada and down into the continental U.S. Wintering grounds extend from just above the Canadian border to California in the West and North Carolina in the East. Some particularly ambitious individuals have gotten as far south as Florida and the Gulf Coast states. The rough-legged hawk is called a buteo, meaning that it is a soaring hawk related to other buteos such as the red-tailed hawk and the broad-winged hawk. The rough-leg has long wings and a long tail, which means that it is a powerful flier, and it seems to ride thermals (uprising currents of air produced by the heated earth) less than other hawks. This characteristic not only means that this species will cross open water (many raptors are reluctant to do so), but that migrating rough-legs may opt to get airborne in the cool morning hours, before thermals develop. Hawk-watchers report that this bird is typically the first buteo seen in the morning, and the last to be observed in the late afternoon. As is the case with most other raptors, female rough-legs are larger than males. Females average 2 pounds, 13 ounces, with a wingspan of up to 56 inches. Males average 2 pounds, 4 ounces, with an average wingspan of 49 inches. This is a large buteo, in the East exceeded only by the red-tailed hawk in weight. In wingspan the rough-leg actually exceeds the chunkier red-tail. When the rough-leg glides or soars, its wingshape is distinctive. Near the body the wings are held upswept in a pronounced dihedral (V-shape). Near the wrist or carpal joint the wings level out. At the carpal joint there is a characteristic dark patch of feathers that helps observers identify this hawk in flight. The two-toned rough-leg is vividly patterned, in contrast to the more subtly colored red-tail and broad-wing. The flight feathers (the big feathers of a bird's wing and tail that make flight possible) are silvery at the base and dark at the tip. While both male and female rough-legs exhibit the two-toned plumage, they are different in other ways, and juveniles or immatures (young birds) differ from the adults. Complicating identification is the fact that this species occurs in dark and light morphs or phases (inherited color differences that are unrelated to age, season or gender). However, this bird's behavior and its migration patterns help us to recognize it. The rough-leg is typically found in New England only from November through March. Wintering areas will be places that remind the hawks of their northern open-country home. So wintering rough-legs will be attracted to farm fields, marshes, grasslands and even the occasional airport. Fields spread with manure are particularly attractive to these hawks, since opportunistic rodents will move in to feed on the grain in the manure. The equally opportunistic rough-legs will then move in to feed on the rodents. This species is nomadic over its winter range, moving about as the food supply dictates. This is our only buteo that hovers, flapping its wings vigorously as it sweeps its head back and forth in the search for voles and mice. At other times it may fly low and slow, or it may still-hunt (hunt by sitting motionless and watching) from a perch. If the hunting is good a number of rough-legs may gather in one area and roost communally. When the food supply dwindles, the hawks move on as a group.
The number of rough-legs that visit the lower 48 states
varies considerably from year to year. Roughly every 4 or 5 years the
U.S. is host to unusually large groups of these winter migrants. These
irruptions occur because on their home territory rough-legged
hawks are heavily dependent on lemmings and voles for food. With their
proportionately small, weak feet the rough-legs cannot prey on larger
species, such as arctic hares and ptarmigan. The problem with lemmings
and voles is that these little rodents are subject to cycles of population
buildups and crashes. When their prey species become scarce, rough-legs
make themselves scarce as well; virtually the entire population heads
south. |