Rough-legged Buzzard
| Rough-legged Buzzard | |
|---|---|
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| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Falconiformes (or Accipitriformes, q.v.) |
| Family: | Accipitridae |
| Genus: | Buteo |
| Species: | B. lagopus |
| Binomial name | |
| Buteo lagopus (Pontoppidan, 1763) | |
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Summer Winter | |
The Rough-legged Buzzard (Buteo lagopus), called the Rough-legged Hawk in North America, is a medium-large bird of prey. It is found in Arctic and Subarctic regions of North America andEurasia during the breeding season and migrates south for the winter.
The species exhibits a wide variety of plumage patterns including light and dark morphs. Nests are typically located on cliffs, bluffs or in trees. Clutch sizes are variable with food availability but 3–5 eggs are usually laid.These hawks hunt over open land, feeding primarily on small mammals. Along with the Kestrels,Kites and Osprey, this is one of the few large birds of prey to hover regularly.
Description
This fairly large raptorial species is 48–60 cm (19–24 in) with an average wingspan of 120–153 cm (47–60 in).Individuals can weigh from 600 to 1,800 g (1.3 to 4.0 lb) with females typically being larger and heavier than males. The plumage is predominantly brown in colour and often shows a high degree of speckling. A wide variety of plumage patterns are exhibited in light vs. dark morphs, males vs. females and adults vs. juveniles. Extensive field experience is required to distinguish between certain plumage variations.Compared to its more common cousins, the Common Buzzard and the Red-tailed Hawk, it is slightly larger, though may be outweighed by the latter.
Compared to the Common Buzzard, it is longer-winged and more eagle-like in appearance. Distinguishing characteristics in all plumages include long white tail feathers with one or more dark subterminal bands. The wing tips are long enough to reach or extend past the tail when the animal is perched. Its feet are feathered to the toes (hence its scientific name, lagopus, meaning "hare-footed") as an adaptation to its arctic home range. Lagopus is derived from Ancient Greek lago(λαγως), meaning "hare", and pous (πους), meaning "foot".Its talons are relatively small, reflecting their preferred choice of prey. A broad brown chestband is present in most plumages and a square dark carpal patch contrasting with the white under-wing is an easily identifiable characteristic in light morph individuals.
It is the only hawk of its size to regularly hover over one spot, by beating its wings quickly.
Taxonomy
The Rough-legged Hawk is a member of the genus Buteo, a group of moderately large raptors exhibiting broad wings, short tails and wide robust bodies. This group is known a hawks in North America but referred to as buzzards in Europe.
There are at least 3 recognized subspecies of Buteo lagopus:
- B. l. lagopus is the nominate subspecies. It breeds in northern Europe and Asia and has relatively dark plumage. The dorsal feathers are a homogeneous brown colour, contrasting well with the paler head.
- B. l. sanctijohannis breeds in North America. It has pale, speckled dorsal plumage and is slightly smaller than B. l. lagopus.
- B. l. kamtchatkensis breeds from north Siberia to Pacific North America. It has paler plumage when compared with B. l. sanctijohannis.
Habitat and distribution
The Rough-legged Hawk breeds in tundra and taiga habitats of North America and Eurasia between the latitudes of 61 and 76° N. Rough-legged Hawks occurring in North America migrate to the central United States for the winter, while Eurasian individuals migrate to southern Europe and Asia. During these winter months, from November to March, preferred habitats include marshes, prairies and agricultural regions where rodent prey is most abundant.
Breeding sites are usually located in areas with plenty of unforested, open ground. Depending on snow conditions, migrants arrive at breeding grounds during April and May. Home ranges vary with food supply but are commonly reported to be 10–15 square kilometers during the winter, but little is known about home ranges during the breeding season. Although frequently attacked by other bird species such as Gryfalcons and Skuas, the Rough-legged Buzzard is not strongly territorial.
Behaviour
Diet
This species is carnivorous, typically feeding on small mammals, which make up 62–98% of its diet. Lemmings and voles are the major prey items but this varies with seasonal availability. Some evidence suggests that these hawks may be able to see vole scent marks which are only visible in the ultraviolet range, allowing them to cue in on prey.The Rough-legged Hawk will also supplement its diet with mice, rats, gerbils, pikas and insects.Ptarmigan, Lapland Longspur and American Tree Sparrow are species commonly reported as preferred avian prey. Waterfowl, shorebirds and Short-eared Owls are hunted less frequently. When small mammals are scarce, the Rough-legged Hawk will also feed on medium sized mammals including prairie dogs, ground squirrels, muskrats and weasels. During winter, shrub-steppe habitats seem to encourage a strong dependence on rabbit prey.
This avian predator hunts opportunistically, feeding occasionally on carrion, but focusing primarily on most available food types. Rough-legged Hawks will steal prey from other individuals of the same species as well as other species such as the Red-tailed Hawk, Northern Harrier,American Kestrel and Raven. Prey sizes range from 6.5–2,587 g and adults require 80–120 g of food daily. Individuals hunt during the day time, often hovering above the ground in search of prey.
Reproduction
Sexual maturity is reached at about two years old. Breeding generally occurs during May but is variable depending upon dates of arrival at breeding grounds. The Rough-legged Hawk is thought to be monogamous, mating with a single individual for multiple years.No evidence currently suggest otherwise.
Nests are built soon after arrival to breeding grounds and require 3–4 weeks to complete. Twigs, sedges and old feathers are used as building materials. Nests are 60–90 cm in diameter and 25–60 cm in height. Cliff ledges and rocky outcroppings are preferred nesting sites. Females can lay 2–7 eggs but will typically lay 3–5. Average egg size is 56.4 mm in length by 44.7 mm in width. Minimum incubation period is 31 days, provided almost exclusively by the female. The male feeds the female during this incubation period. After hatching, young require 4–6 weeks before fledging the nest. Fledglings depend on parents to provide food for 2–4 weeks after leaving the nest.
Vocalization
Adult Rough-legged Hawks will vocalize alarm calls when intruders approach a nesting site. It is described as a downward slurring whistle, sounding like kiu wiyuk or a lengthy descending kee-eer similar to that of the Red-tailed Hawk. This cry is given in flight or from a perch every 15–30 s. During courtship, both sexes have been recorded to give a whistling sound that changes to a hiss. Following copulation, females will give a clucklike sound and males vocalize a whistling noise. Fledglings will give begging calls while waiting for parents to provide food.
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