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Buteo lagopusrough-legged buzzard(Also: rough-legged hawk)

By Garrett Good

Geographic Range

Buteo lagopus has a nearly holarctic distribution. Its geographic range includes most of the United States and all of Canada. Rough-legged hawks spend their winter months in all of the United States except for North Carolina and along the southeast coast of the United States, Kentucky, Alabama, Mississippi, and Arkansas. They are found as far north as Newfoundland and as far west as central Europe and parts of Russia. (Pearson, et al., 1936)

Habitat

Rough-legged hawks inhabit open country and agricultural lands. They are more common in open, early successional areas in which they can soar and seek prey in grasslands and shrublands. Once migration is complete they settle in a suitable nesting spot with enough food nearby to sustain them. Their nests are usually located in trees or on a rocky cliff in which they can overlook a field to catch prey for themselves and their young. (Pearson, et al., 1936; Bechard and Swem, 2002; Terres, 1980)

Physical Description

Adult rough-legged hawks average 1026 g and have a wingspan of 134 cm. Total length averages 53 cm. Females are typically the larger gender. Rough-legged hawks have eight different morphs that vary between sex, age, and location. Both sexes exhibit both light and dark morphs; and coloration varies between juveniles and adults.

All adult morphs have a black band that goes along the edges of the underside of their lesser coverts. Adults also all have dark colored eyes. Juveniles have light colored eyes and a dark band along the underside of their wings.

Light morphs of adult females have brown backs and a pattern of increased markings from breast to belly. They have one dark tail band and heavily marked leg feathers. Light-morph adult males have grayish backs. Their breasts are more heavily marked than the belly and multiple bands exist on the tail. A light-morph adult male has heavily-marked leg feathers.

Dark-morph adult males are almost completely black but can be brownish with several white bands on their dark tail. Dark-morph adult females are dark brown with a single black band underneath their tail. Dark-morph juveniles are similar to adult females but exhibit rusty bands underneath their wings and tails. Some individuals have a pale-brown head. (Wheeler and Clark, 1996)

  • Sexual Dimorphism
  • female larger
  • sexes colored or patterned differently
  • Range mass
    745 to 1380 g
    26.26 to 48.63 oz
  • Average mass
    1026 g
    36.16 oz
  • Range length
    46 to 59 cm
    18.11 to 23.23 in
  • Average length
    53 cm
    20.87 in
  • Range wingspan
    122 to 143 cm
    48.03 to 56.30 in
  • Average wingspan
    134 cm
    52.76 in

Reproduction

Buteo lagopus will usually migrate solo (very uncommon to fly in groups) and find a mate once they have reached their destination. Males will soar and circle until a female joins them. Rough-legged hawks perform courtship displays in the late winter, once it has began to get warmer and flying conditions improve. After a male is joined by a female, both sexes soar together with their tails and wings fully spread. Males then perform a "Sky-Dance" dislay, in which they soar high, suddenly dive, climb again, free fall, and finally, climb back up to a normal soaring height. Male rough-legged hawks defend their mates from other males by taking flight and chasing rival males.

Male and female rough-legged hawks build a nest together after they have found a suitable site on a rocky cliff. Males carry most of the building supplies while females construct the nest of twigs, grass, molted feathers, and fur from prey. Even objects such as caribou bones are sometimes incorporated into nests. Nests take three to four weeks to build and are usually 60 to 90 cm in diameter and 25 to 60 cm deep. (Bechard and Swem, 2002)

Rough-legged hawks breed once a year, usually between April and June, but breeding has also been reported in July. There are 2 to 7 eggs per clutch and they take a minimum of 31 days to hatch. Fledging usually takes more than 40 days, although some fly weakly at 31 days old. The young are not fully independent of the parents until 2 to 4 weeks after they leave the nest, at 55 to 70 days old. The period of independence sometimes extends into migration. Sexual maturity of males and females is reached at 2 to 3 years. (Bechard and Swem, 2002; Terres, 1980)

  • Breeding interval
    Breeding occurs once a year.
  • Breeding season
    Breeding typicalls occurs from April to June, occasionally July.
  • Range eggs per season
    2 to 7
  • Average eggs per season
    4
  • Range time to hatching
    31 (low) days
  • Range fledging age
    31 (low) days
  • Average fledging age
    40 days
  • Range time to independence
    55 to 70 days
  • Range age at sexual or reproductive maturity (female)
    2 to 3 years
  • Range age at sexual or reproductive maturity (male)
    2 to 3 years

Both male and female Buteo lagopus provide for and protect their young from the time the eggs are laid until the young hawks are independent (55 to 70 days post-hatching). After the eggs are laid, the female will incubate them, while the male will hunt for food for both parents. The male will continue to hunt for both adults until the young hatch. Once the young have hatched, the female will begin to hunt to ensure that there will be enough food for both the young and the adults. Both parents will also guard the nest and ward off other birds and predators. (Pearson, et al., 1936; Morneau, 1994; Smith, 1987)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female
    • protecting
      • male
      • female

Lifespan/Longevity

Rough-legged hawks can live up to 18 years in the wild. However, the average life span is about 2 years, largely because most young birds do not survive. Once they survive their fledging stage and first year, rough-legged hawk annual survival improves. Deaths often result from illegal shooting or trapping activites, collisions with human structures, such as powerlines or radio towers, and collisions with vehicles. In captivity, the longest living reported rough-legged hawk was 17 years old. However, a rough-legged hawk at the Pocatello Zoo, in Idaho, came in as an injured adult in 1987 and remains alive as of July 2009, making her over 24 years old. (Bechard and Swem, 2002; Terres, 1980)

  • Range lifespan
    Status: wild
    18 (high) years
  • Range lifespan
    Status: captivity
    24 (high) years
  • Average lifespan
    Status: wild
    1.7 years

Behavior

Buteo lagopus is usually a solitary species but they occasionally migrate in small groups. Rough-legged hawks typically fly relatively low for birds of their size. They use wing-flapping to reach a preferred altitude, but then usually glide until a perch or a source of food is spotted. They are not known to walk at all, but rough-legged hawks have been spotted scooting down a perch to move closer to a mate or towards food. (Bechard and Swem, 2002)

  • Range territory size
    3.6 to 11.8 km^2
  • Average territory size
    7.3 km^2

Home Range

Rough-legged hawks have average territories of 7.3 square kilometers (range 3.6 - 11.8 square km).

These are territorial hawks and generally do not tolerate other nests within 1 km. Rough-legged hawks have been known to share cliff nesting spots with gyrfalcons Falco rusticalus and peregrine falcons Falco peregrinus as well as other rough-legged hawks, but only if the cliff is large and the nests are at least 30 m apart. They will avoid nesting within 60 m of any potential predators of their young, such as golden eagles. They will defend their nests from any bird that threatens them or their young. (Bechard and Swem, 2002)

Communication and Perception

Rough-legged hawks use sight and vocalizations to communicate with others. They use many calls for communication with other hawks such as a warning call (a high pitch shriek), a courtship call (a low whistle that turns into a hiss), and a "normal" call (a high-pitched whistle into a shriek). Rough-legged hawks are usually silent when away from the breeding site except when in competition with another male or threatened. Males may broadcast 100 calls per minute; much more often than females. (Bechard and Swem, 2002; Terres, 1980)

Food Habits

Rough-legged hawks are swift hunters than spot and capture prey with great precison. Rough-legged hawks will perch high in trees or soar in the sky where they can scan a field or grassy area for small prey. After the prey have been spotted, hawks take flight as quietly as possible (unless already in flight) and circle above a few times to ensure there is no competition with other birds of prey. They dive and spear prey with their large talons. They return to a perch to consume the meal. Typical prey include mice, shrews, black tailed prairie dogs Cynomys ludovicianus, small birds, and other squirrel species (Spermophilus and Tamias). (Pearson, et al., 1936; Reid, et al., 1997; Seery and Matiatos, 2000)

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
  • Animal Foods
  • birds
  • mammals
  • reptiles

Predation

Their are many known predators of Buteo lagopus but most are predators of nestlings. Humans cause death in many rough-legged hawks by shooting, trapping, hitting them with cars, and building structures that the hawks fly into. Known predators of Buteo lagopus also include artic foxes (Vulpes lagopus), grizzly bears (Ursus arctos), and many other species of birds of prey. Most adult hawks are killed by these predators while trying to scare them away from their nests but artic foxes and other hawks are known to get into the nest and eat the eggs or nestlings. (Bechard and Swem, 2002; Pearson, et al., 1936)

Ecosystem Roles

Rough-legged hawks help to control the populations of small mammals. Their nests are usually built where there is high prey density.

These hawks are hosts to many parasites, including several nematodes in the genus Physaloptera. A hematozoan documented in this species is a Leucocytozoon species. (Morgan, 1943; Reid, et al., 1997; Stabler and Holt, 1965)

Commensal/Parasitic Species
  • Physaloptera
  • Leucocytozoon

Economic Importance for Humans: Positive

Buteo lagopus helps control pest (mice, moles, rats) populations through predation. (Reid, et al., 1997)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

There are no known adverse effects of Buteo lagopus on humans.

Conservation Status

Buteo lagopus is rated as "Least Concern" on the IUCN Red List. Protected under the U.S. Migratory Bird Act, these birds cannot be hunted or killed except for scientific purposes.

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Garrett Good (author), Radford University, Karen Powers (editor, instructor), Radford University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

holarctic

a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

References

Bechard, M., T. Swem. 2002. Rough-legged Hawk; Buteo lagopus. The Birds of North America, 641: 1-31.

Dunne, P., D. Sibley, C. Sutton. 1988. Hawks In Flight. Boston: Houghton Mifflin Company.

Morgan, B. 1943. The Physalopterinae (Nematoda) of Aves. Transactions of the American Microscopical Society, 62/1: 72-80.

Morneau, 1994. Breeding density and brood size of rough-legged hawks in northwestern Quebec. The Journal of Raptor Research, 28/4: 259-262.

Mueller, H., N. Mueller, D. Berger, G. Allez, W. Robichaud. 2000. Age and sex differences in the timing of fall migration of Hawks and Falcons. Wilson Bulletin, 112: 214-224.

Pearson, T., J. Burroughs, E. Forbush, W. Finley, G. Gladden, H. Job, L. Nichols, J. Burdick. 1936. Rough-legged Hawk. Pp. 79-80 in Birds of America, Vol. 1-3, 12 Edition. Garden City, New York: Garden City Publishing Company, Inc..

Reid, D., C. Krebs, A. Kenney. 1997. Patterns of Predation on Noncyclic Lemmings. Ecological Monographs, 67: 89-108.

Seery, D., D. Matiatos. 2000. Response of wintering buteos to plague epizootics in prairie dogs. Western North American Naturalist, 60: 420-425.

Smith, C. 1987. Parental roles and nestling foods in the rough-legged hawk, Buteo lagopus. ONT. FIELD-NAT, 101: 101-103.

Stabler, R., P. Holt. 1965. Hematozoa from Colorado Birds. II. Falconiformes and Strigiformes. The Journal of Parasitology, 51/6: 927-928.

Terres, J. 1980. Rough-Legged hawk. Pp. 485 in The Audubon Society Encyclopedia of North American Birds, Vol. 1, 1 Edition. New York: Alfred K. Terres.

Wheeler, B., W. Clark. 1996. A Photographic Guide to North American Raptors. San Diego, CA: Academic Press Inc..

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