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How did it get its name?
The Rough-legged Hawk (Buteo lagopus), is a medium-sized, broad-winged soaring raptor. It originally was called the American Rough-legged Hawk, later changed to the Rough-legged Hawk because the bird was found to occur breeding in the boreal areas outside of North America as well. Interestingly enough, the first type specimen for this species came out of Denmark in 1763, well before the first North American specimen from Newfoundland was described in 1788. In Eurasia, this same species is called the Rough-legged Buzzard. A translation of the Latin term "buteo" means "buzzard". So in our lifetime, don't be surprised to someday find the Rough-legged Hawk to be finally called its rightful English name, the Rough-legged Buzzard. It will eventually be called this universal English name for conformity sake; it is just a matter of time.
The Latin term "lagopus" has a dual prong interpretation: "lagos" meaning both ptarmigan and also hare, and pous meaning foot. In other words, "feathered or hairy feet". The bird is called the Rough-legged Hawk, because the feathers extend down to the base of the toes. This unique morphology only occurs in two other diurnal (daytime active) North American raptors, the Ferruginous Hawk (formerly called the Ferruginous Rough-legged Hawk) and the Golden Eagle.
Morphological Adaptations to their Cold Environment
The first feature that strikes anyone observing Rough-legged Hawks is their characteristic plumage coloration, most notably their unique black and white, black and cream, or black, brown and cream coloration depending on how detailed you want to be.
This plumage coloration allows these birds to blend in with their oftentimes snowy or snow patch lanscape. But these birds, since they are buteos, exhibit a high degree of plumage color variation. Most typical are the light morphs or forms described above. The old bird books used to call these plumage differences "phases" (e.g. light phase or dark phase), but phase denotes change and it must be understood that once a Rough-legged Hawk is born with a light coloration is remains this coloration its entire lifetime, and the same is true for dark forms as well. Therefore technically speaking they are called morphs or forms. In addition it must be understood there are intermediate morphs (i.e. dark/light combination) and dark morphs of the Rough-legged Hawk as well. But the intermediate forms are not as numerous and the dark morphs are the most unusual in the population. But, it is important to know they do occur. Light morph Rough-legged Hawks are best told by their blonde colored heads, blonde bibs, and black or dark brown bellies. But in some individuals the pattern can be reversed. Nearly all light and intermediate morphs when they fly, have dark carpal or wrist spots in their underwing, and a black terminal band and a white base pattern on their tail. Adults and juvenile birds and male and females have slightly different or subtle plumage differences and can be most evident when viewing the more typical light morphs. Light morph adults have streaked chest and underwings, blonde heads with dark eyes, a clearly demarked terminal band on the tail, and black bellies. Juveniles tend to lack streaking on the chest and underwings, and have blonde heads with lighter eyes, a diffuse terminal band on the tail, browner bellies, and whitish wing panels on the upper part of the wing. Typical males are grayer overall and have more of a barred pattern, particularly on the breast, belly, flanks, and tail. The dark morphs tend to become difficult ID's, but most usually exhibit some brown or gray on the upper part of their outer wing. But the best characteristics to shoot for in these difficult circumstances are the tiny feet feathered to the toes, the small head, small beak and gaping mouth, and whether it hovers while in hunting flight. In the winter it also can hunt from stationary perches such as fence posts, telephone poles, trees, hills, and even while on the ground.
Unique Hunting Technique
Few North American raptors truly hover. Hovering is basically wing movement which results in stationary flight. The key here is that in order for a bird to truly hover, it needs to be suspended in the air totally by way of wing motion without assistance from the wind. Right off hand only three North American raptors fit this category regularly: the American Kestrel Falco sparverius, the Osprey Pandion haliaetus, and the Rough-legged Hawk. It should be footnoted, the Ferruginous Hawk Buteo regalis does hover on occasion, but not on a regular basis as does the three species mentioned above. Hovering is simply a hunting technique that allows a species an opportunity to occupy open terrain with or without wind in search of prey. In the case of the Rough-legged Hawk, the prey they are searching out in the summer habitat of open tundra/semi-open taiga are primarily lemmings, mice and voles in the arctic, or voles and mice in the open fields, farmlands, grasslands, prairies, marshes, and meadows of the temperate zone in the winter. Since Rough-legged Hawks possess such small feet, it allows them the opportunity to handle very small prey with intricate precision. In addition, the feathering down to the toes allows the feet to stay warm during cold periods.
Boreal/ Panboreal Nesting and Boom and Bust Production
Rough-legged Hawks are both boreal and panboreal nesters, depending on the scale by which it is viewed. For the purposes of this discussion, the term "boreal" simply encompasses both taiga (transitional semi-open coniferous forests south of the tundra) and tundra habitats. Whereas, the term "panboreal nesting" means that this bird nests in the boreal regions of the world. Rough-legged Hawks typically nest on cliffs in the panboreal zone, but also can be found on escarpments, hills, and even small trees and artificial structures such as oil derricks on occasion. Their nest is a raised foundation comprised of small twigs and occasionally mixed with salvaged bones and other small debris. On their breeding grounds they perform a sky dance display in which they flap and soar to high elevations, then stoop and descend in the vicinity of the nest. They typically lay 2-6 eggs, with the incubation period 31 days and fledge 38-45 days after hatching. Breeding success of Rough-legged Hawk production in the panboreal zone is often a reflection of population cycles of lemmings and voles. During stressful food periods they have been known to eat birds, insects, ground squirrels, and even carrion. For example in Norway, lemming cycles occur every 3-5 years. Lemmings typically migrate at night and move twice annually, once in the spring when the snow melts, and the other in the fall forcing lemmings in higher density sites to be the first ones to move. Besides seasonal shifts based on food supply, there are also altitudinal shifts of lemmings to lower elevations such as coastal plains in the fall and higher elevations in the summer. These boom and bust prey cycles are then reflected in Rough-legged Hawk production.
An Avian Migrant that Winters in Montana
The autumn exodus of the Rough-legged Hawk from their panboreal breeding range, to the pantemperate wintering areas in central United States and central Eurasia, varies according to food supply, temperature, photoperiod (length of light in a day),and snowfall. It is the only buteo in existence directly associated with cold climates. During mild winters and/or when prey numbers are high, these birds have a tendency to stay longer and/or further north. Rough-legged Hawks are diurnal migrants. Although some individuals depart in late summer, the bulk of the Rough-legged Hawks leave the boreal home areas from mid to late September arriving in Montana in force from mid-October through November. Banding studies have shown the majority of birds from Alaska typically winter west of the Continental Divide, whereas birds from the western Canadian archipelago mostly winter on the Great Plains, however there is a degree of overlap in winter ranges. In the United States, the principal wintering areas are found in the west, such as: Klamath Basin in Oregon, Great Salt Lake in Utah, Snake River Plain in Idaho, eastern Oregon, western Montana, northern Nevada, eastern Colorado and western Kansas, and isolated areas in the east such as northern Iowa, the Great Lakes region, in addition to New Brunswick (Canada). Wintering hot spots for Rough-legged Hawks in Montana include: intermountain valleys of western Montana, Gallatin Valley, Paradise Valley, Helena Valley, Freezout Lake and the East Front of the Rockies, and the Great Falls area to name a few. If the winter vole population is high and the weather favorable, they have tendency to stay in the immediate area for much of the winter. However, if the prey availability changes such as in the form of deeper snows or milder weather, their movements during the winter period can become very nomadic. As spring approaches, Rough-legged Hawks begin exiting Montana in force from mid-February through mid-April, and arriving on their boreal nesting areas from April through mid-May completing the annual migration cycle.
So if you are rancher or farmer and you see these black and white hawks that sort of look like something out of winter on your property, enjoy them for their beauty and behavior and realize the important role Rough-legged Hawks play in reducing vole and mice numbers. For the general observer or even a more serious bird watcher, as you drive down the road take a closer look at Montana's Feathered Harbingers of Winter and realize it won't be long before they are gone and back again thus completing the ancient annual migration cycle that probably dates back to late Pleistocene.
Now that the reader has a better understanding of the winter ecology of the Rough-legged Hawk, the next topic scheduled for the March issue of Montana Best Times will be about Great Horned Owls.
Enjoy! And the Best of Big Sky Birding to you!
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