King Buzzard
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King Buzzard (Helle Morphe ) |
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| Buteo regalis | ||||||||||||
| ( GR Gray , 1844) |
The king buzzard ( Buteo regalis ) is a powerful bird of prey that belongs to the genus of buzzards ( Buteo ) within the family of hawks (Accipitridae). It is the largest and heaviest buzzard in the world. As a breeding bird, the species is restricted to southwestern Canada and the western United States . The birds that breed in Canada and the northern USA are migratory birds with wintering areas in the southern part of the breeding area, as well as southwards to central Mexico , approximately up to the level of the Río Lerma Santiago river system. The king buzzard prefers low-lying areas, but rises in the foothills of the Rocky Mountains up to about 1500 meters. It is a bird of prey in open landscapes such as prairies , sagebrush - steppes and semi-deserts . In these often treeless habitats , it builds its nest on higher specimens of the bush vegetation, on structures built by hand, on cliffs and occasionally on or near the ground. Although he uses some hunting techniques, he is mainly a hide hunter . Despite a multitude of different prey animals, the species is largely dependent on only a few medium-sized rodents such as rabbits , ground squirrels and prairie dogs , which make up a large part of the ingested biomass. Their presence also determines the clutch size and escape rate.
The royal buzzard is - like many types of buzzards - very variable in color. It appears in two color morphs , a light one, which comprises about 90% of the population, and a dark one. The sexes show no color dimorphism , females are slightly larger, but significantly heavier than the males.
The species is monotypical . As a sister species that is rough-legged buzzard ( Buteo lagopus ) adopted, the Upland Buzzard belongs to the next relationship. According to the IUCN , the species population is not endangered. The breeding population of the species has increased significantly over the past 50 years. As of the end of 2019, the number of adult royal buzzards is estimated at 110,000 individuals.
Appearance
The king buzzard is a massive, massive bird of prey whose light morphology appears largely white on the underside and chestnut brown on the top. Overall, however, the light morph on the underside is very variable in color, so that there are almost white individuals as well as birds with extensive and intense rust-brown markings. The dark morph is dark brown on the top, bottom and head, the feather feathers of the wings are dark brown, in sharp contrast to the light silver-gray wings . The body length is between 56 and 69 centimeters, the body weight between 977 and 2074 grams. The two sexes do not differ in color, females are on average 2–7% larger and up to 17% heavier.
The king buzzard is well marked due to its size, its very light (or very dark-gloomy) appearance and its powerful, strikingly yellow, deeply split beak. Also striking is a rust-brown V in front of the base of the tail, which is formed by the rust-red fletching of the legs .
Light morph
The majority of the royal buzzards belong to the light morph. In some populations dark colored individuals are completely absent, in others up to 10% of the individuals can be dark morphous.
The back, shoulders and flanks are usually dull chestnut brown. Most of the feathers have a creamy brown edge, which creates a speckled impression overall. The large head is darkly dashed on a light gray-brown background; this gray-brown color changes in the area of the mantle into the brown color of the dorsal plumage. The mighty blue-gray hooked bill is deeply split and clearly marked yolk yellow. In the basal third it is surrounded by a yellow wax skin . The cleft beak extends to mid-eye level. The iris is usually dark yellow or chestnut brown. The underside is very light. Throat, chest and belly are dashed or spotted with rust-brown dots or spots of varying intensity on a pure white, occasionally yellowish or brownish airy background. Especially the lower side of the abdomen and the rear flanks often have more intense spots. The white wings are often indistinctly banded and indistinctly darkly bordered on the underside of the subterminal; the deeply fingered hand wings are dark brownish in the terminal half. The lower elytra are speckled with varying degrees of intensity rust-red, a color detail that was decisive for the English name of the species Ferruginous Hawk . These color elements are often arranged in a line. The wings are brownish on top. When the wings of the hand are spread, a clear, bright window appears in their basal area. Most of the inner flags of the arm wings are light gray to whitish, which means that the inner hand wings and the arm wings have a slight light-dark shade on the upper side. The rump is rust-brown, the tail is white on the upper side with an often slightly brownish border of the control feathers, on the underside white with only hinted at subterminal and terminal bands . The densely feathered runs are bekrallten to the solid, orange-yellow dense rust toes (yellow greenish in adult individuals in food stress) on a light background, along linear cuckoo . This drawing forms a conspicuous V in the flying bird with its legs drawn up.
Dark morph
From a distance individuals of the dark morph appear uniformly dark-gloomy black-brown. More precise color gradations can only be determined up close.
The plumage of the entire upper side is matt dark brown, sometimes a little lighter reddish brown. Most of the feathers have a slightly lighter edge, creating an indistinct speckle. In the nape of the neck, some white or silver line-shaped color elements can often be seen. The top of the head and forehead are also mostly unmarked black-brown. Only the area between the base of the beak and the eye is a little lighter, often a lighter stripe above the eye can be seen. The basal third of the dark horn-colored beak is covered by a yellow wax skin. The top of the wings is dark brown, with the upper wing-coverts being slightly lighter than the more black-brown wings. In their basal section, the spread hand wings show a clearly silver-colored window. The entire underside and the under wing-coverts are almost unmarked black-brown. Only in the chest area do some light, whitish welts loosen up this dark color scheme. The feathered legs are obscured dark reddish brown. The outer, deeply fingered hand wings are dark silver-gray and clearly bordered gray-black, the other wings are whitish with slightly brownish edges and a rather indistinct gray-brown subterminal band. The tail is light silver on the top and largely white on the underside. The iris is yellow-orange, the toes are yellowish.
Youth plumage
Between August of the year of birth and May of the following year, young birds show their juvenile plumage. On the upper side it is darker than the adult plumage, usually without rust-brown or light chestnut brown parts. White feather bases are more common and noticeable than in adult plumage, especially in the coat and neck area and on the top of the head. The light stripe above the eyes, which almost disappears in the adult plumage of the light morph, is clear. The chest has a distinctive brown-orange tint in the form of a breast flap. The lower breast and the abdomen as well as the under wing coverts are rather sparsely matte dark brown mottled; the typical bright rust-brown color elements of the adult plumage are missing. The coloring of the wings and the control feathers largely corresponds to that of adult buzzards, while the yellowing of the wax skin and toes is noticeably paler. The fletching of the legs is almost pure white, so that the V-sign of the flying colored king buzzards is missing.
flight
The wingspan of the species is about two and a half times the length of the body, i.e. more than 1.5 meters. Royal buzzards fly with slow, deeply sweeping, powerful wing beats and sail with a slight V-position with deeply fingered outer hand wings. The species can also shake for a short time . In the pre-breeding season they circle in thermal tubes and rise high. Prey animals are usually carried to the nest in one catch.
Mauser
Nestlings start changing downy plumage at around two weeks. They first molt the small and body plumage, then the wing covers, the wings and the control feathers, and finally the head plumage. This moulting lasts between 25 and 40 days and is largely over when it is released. Before moulting into the definitive adult plumage begins in May of the next year, some partial moulting of the body plumage, sometimes also individual wings and control feathers, may have preceded. This moult, in which the entire plumage is moulted in several individual stages, lasts up to 100 days. Breeding birds begin to change their feathers during the breeding season (females already in the laying period). This moulting is interrupted in the nestling season and continued after the breeding season. Usually it is only completed in winter quarters.
Vocalizations
King buzzards are acoustically rather inconspicuous. Nestlings make soft begging noises. Adult birds can only be heard more frequently in the pairing period and the pre-breeding season; outside of this time you hardly hear the species, even when several individuals are together. The most common sound is a buzzard-typical, elongated, often slightly tremolating Wiiiiiiiiääh , which is uttered at relatively large intervals mostly by flying, and occasionally also by sitting individuals. In the pairing period it serves as a contact call and is used to demarcate the territory; a short, sharp Wiääh, which is clearly emphasized on the first syllable and usually in a row, is a universal alarm call. This call is very similar to the calls of the herring gull .
distribution
The breeding area of the Royal Buzzard is entirely in the southwestern part of Canada (except British Columbia ) and the western and southwestern parts of the USA. It is separated into two different ecoregions by the Rocky Mountains: the grasslands of the prairies east of the Rockies and the scrub steppes and semi-deserts west of the mountains.
In detail, the species is breeding bird in southeast Alberta in southern Saskatchewan and in the extreme southwest of Manitoba . To the south, the eastern border of the breeding area runs in central North Dakota , extends furthest to the east in eastern South Dakota and turns again to the west in Nebraska . Kansas and Oklahoma are only touched in the far west, Texas in the northwest corner of the Texas Panhandle . To the west, the southern border of the breeding area runs in central New Mexico and central Arizona . The western border runs in western Nevada and reaches California in the state's northeastern border area. The northernmost breeding grounds of the king buzzard in the USA are in east-central Washington . Within this area, the species is absent in much of northeastern Idaho , western Montana, and northwestern Wyoming, as well as central and southwestern Colorado . The Black Hills in South Dakota are also not populated. From British Columbia there is only one breeding record from 1968; the first broods in California were recorded in 1988
Winter spread
The winter quarters of the species are in the southern areas of the year-round breeding area, in California and the southern states of the USA. They reach the Pacific Ocean in California and the Gulf of Mexico in Texas . It is believed that around 20% of migrating Royal Buzzards overwinter in Mexico, most of them in the northern areas. However, individual records also come from areas in central Mexico, southwards to the vicinity of Mexico City . Since around 2000, an increasing number of winterers has been recorded in northern regions such as Montana and Idaho.
Migratory behavior
The populations of Canada and those of the northern United States are mandatory migratory birds. Their wintering areas are in the southern areas of the year-round breeding area, on the Pacific coast to Baja California and partly, albeit in small numbers, on the Gulf of Mexico. There are few ring finds from Mexico; the feedback suggests that the majority of winterers stay in the northeastern states, where the last colonies of the Mexican Prairie Dog are. A small number moves on to central Mexico; these birds cover migration distances of over 5000 kilometers; however, most of the migrating king buzzards are short-range migrants . Fledglings leave their place of birth first. Usually they leave soon after leaving in July or August and initially roam around in an undirected way, only to gradually take a southerly direction. As soon as airworthy plumage is available again after moulting, the females follow. Finally, the males leave, and their departure can last until the beginning of October
The North American continental watershed also largely determines migratory behavior. Only 4.7% of the birds ringed east of this watershed were found west of it in winter; however, western birds overwinter more frequently in the eastern half.
They move home in late winter and early spring. At the end of March / beginning of April most of the breeding sites are occupied again.
habitat
Breeding area
The breeding area of the king buzzard is separated into an eastern and western part by the main ridge of the Rocky Mountains, in each of which different ecoregions predominate: the flat or rolling grassy areas of the prairies dominate in the east , while the western part is dominated by bush steppes, semi-deserts and deserts. A sufficient supply of prey animals, primarily medium-sized rodents, is the most important requirement for a suitable breeding site. Short-grass sections and areas with little vegetation are preferred because the prey animals can be reached more easily. Likewise, suitable perches - be they of an anthropogenic nature (telegraph poles, irrigation systems, barns and the like) or of natural origin (stone cliffs, tall bushes, trees) - and appropriate nesting facilities are indispensable requisites of a breeding habitat. In general, the species avoids deep canyons , areas over 1500 meters above sea level and extensive forests in both ecoregions .
In the eastern part of the distribution area, the species prefers open - ideally interspersed with trees or rocks - grassland; Trees along small watercourses are also positive for breeding settlement. Agricultural sections and settlements are tolerated to a certain extent. In the western part steppes and semi-deserts dominate the habitat of the species. It breeds in steppes with strongly loosened bush vegetation (sagebrush and stocks of Atriplex canescens (Saltbush)), but avoids areas in which stocks of these species are too dense. In somewhat higher altitudes the species occurs up to the edges of the pine-juniper zone. In these semi-desert areas, easy access to water is an essential prerequisite for breeding settlement.
Wintering area
Breeding birds from the prairie areas also prefer extensive grasslands in winter, especially those where prairie dogs are common. King buzzards of the western steppes and semi-deserts usually look for similar habitats even in winter, although the frequency of important prey animals such as antelope pies , pocket rats and rabbits is more decisive for the choice of winter quarters than its vegetation.
Space requirements and territoriality
The space requirement of the species is very much related to the food supply and the type of landscape. The relevant information is correspondingly broad. While Christie still specifies a minimum size of a breeding area of 430 km², new studies show completely different results. Although the area size of a pair that breeds in a grassland habitat of medium quality is approximately 100 km², breeding areas of only 5.9 km² have been found in Utah and the size of some areas close to the city limits was less than 3 km². So far, the minimum distance between nests in flight has been 3.4 km. When the species establishes winter areas, they are smaller than the breeding areas and are not vigorously defended. In Colorado an average size of 3.53 was found km².
King buzzards are strictly territorial during the breeding season. They vigorously defend at least the core areas of their territory from their own species, but intense contact fights are rare. The edge zones of neighboring territories can overlap. Often other raptors such as the breeding Swainson's hawk and red-tailed hawks or owls as the Great Horned Owl of the Kingdom buzzard within districts. Although they are driven away from the immediate vicinity of the nest, they are tolerated within the area. The winter territoriality is only weak. King buzzards often hunt together and sleep in a sleeping tree just a few meters apart.
Food and subsistence
The prey spectrum of the king buzzard is very large. It includes a wide variety of rodents, many birds , some reptiles, and large insects . Despite this diversity, a few prey animals can be named, the presence of which is essential for this bird of prey and which make up a high percentage of the ingested biomass. For the populations west of the Rocky Mountains these are different species of hare ( Lepus ssp.) And cottontail rabbits ( Sylvilagus ssp.), For the individuals living east of the mountains prairie dogs and ground squirrels. In addition, pocket rats can become the main prey, especially in winter.
These mammals make up about 80% of the biomass on average, and many buzzards purposefully breed near their colonies. Clutch size, breeding success and escape rate depend to a large extent on the presence and number of these prey animals. Birds are eaten regularly. The species spectrum ranges from small songbirds to seagulls and chicken birds , such as the mugwort or the pheasant, which is naturalized in the USA for hunting purposes . In quantitative terms, according to a study from Nebraska, birds are the second most important source of energy, with 12% of the biomass. Royal buzzards also prey on reptiles on occasion, preferring large species such as black snakes or bull snakes . After all, they account for 4% of the biomass supplied. Swarming, large insects, primarily grasshoppers and crickets, as well as various amphibian species are not essential for the energy balance, but are consumed regularly .
The king buzzard has mastered some hunting techniques, but above all it is a high seat hunter. He observes the area from a suitable raised hide, such as a power pole, a higher bush or tree or a rock formation. If it sees suitable prey, it glides from the hide and usually hovers in a low glide flight without flapping its wings over the prey, which it kills on the ground with a strong bite on the neck. The hunting distances seldom exceed 100 meters, the seats are changed regularly. The species also often hunts on the ground by waiting near freshly ejected rodent burrows and preying on careless animals with a flight jump. He pursues fleeing animals over short distances by hopping or jumping wings. Especially pocket rats and ground squirrels often fall victim to the buzzard in this way. In winter several buzzards often hunt down the ground together. Occasionally, mainly along slopes, king buzzards also hunt by means of a slow, low glide flight, which can also be interrupted by shaking phases when the wind is favorable. Occasionally, royal buzzards hunt other, smaller birds of prey, but are also parasitized by golden eagles and bald eagles themselves .
Breeding biology
Pair formation, nest location and nest
It is not known when this species reaches sexual maturity, but the majority of individuals breed for the first time in the spring of their second year of life. Broods of annual birds have not yet been identified. Also the duration and type of couple bond have not yet been adequately researched. The pair bond does not seem to loosen in resident couples after the breeding season; on the other hand, there is no evidence of an upright mating in migrating king buzzards. However, the high level of loyalty to the nest makes re-breeding of last year's partners likely. Royal Buzzards breed once a year; Replacement broods do not seem to take place even with early clutch loss.
In resident couples, pair formation begins as early as the end of February, and in migratory couples immediately after arriving in the breeding area, usually in the second half of March. The courtship ritual is largely limited to sightseeing flights over the area. Above all, the male flies with particularly accentuated wing beats, occasionally flutters, or suddenly falls in a spinning manner. Sometimes the partners also grip each other with their claws and spiral to the ground before they loosen again. Both partners call frequently during these sightseeing flights. Frequent copulations - usually in the vicinity of the nest or on the finished or half-finished nest - are often preceded by such inspection flights, or the male handing over food can initiate copulation. The nest building itself, which begins immediately after arrival in the breeding area, is an essential part of pair formation. During this time, the partners often rest or rest close to each other without having physical contact.
In most of the species' breeding habitats, nesting opportunities above ground level are rare. However, royal buzzards only build their nests directly on the ground if there are no elevated places available. Higher bushes or trees, cliffs, structures of an anthropogenic nature, such as masts of power lines, irrigation systems, drilling rigs and other things, as well as nesting aids on platforms, are clearly preferred. Large-scale studies of both the western and eastern populations have shown that 49% of royal buzzards build their nests in high bushes or trees, 21% in rock formations or on boulders , 12% on structures of anthropogenic origin and 10% on slight elevations. The nest height is accordingly variable and ranges from ground level to about 20 meters above the ground. Recently, more and more artificial nesting platforms have been built, which are also often adopted.
The couple build a new nest or repair an old one within a week. Usually several nests are restored before the eggs begin to lay. The male brings most of the material in, while the female takes more care of the construction. The inner structure consists of rather thin, flexible branches, often of mugwort and other shrubs, which are interwoven with blades of grass. The inside of the bowl, which is around 30 centimeters deep, is lined with soft materials such as animal and plant wool, feathers, but also scraps of paper and other waste. The outer construction consists of stronger branches that are intertwined and wedged together in a very stable manner. In the past, king buzzards often used bison bones for the outer structure . Outside it is often covered with pieces of bark but also with green branches. The nest is already very large as a new building for a bird of this size, but through many years of use it grows to a huge structure with an outer diameter of more than 1.5 meters and an equally high height.
Clutch and young rearing
The laying time is between the 38th and 49th parallel between March 20 and the beginning of May, in northern regions about two to three weeks later. The clutch consists of 2 - 4 (1 - 8) creamy white eggs with the average dimensions of 60.92 mm × 47.75 mm. Mostly they are spotted or spotted brownish, but not infrequently they are also pure white. The laying interval is two days; Breeding begins after the first egg has been laid, so that the nestlings show considerable developmental differences at the beginning of the feeding period. Most of the time the female breeds; it is replaced by the male for short intervals at the beginning of the breeding season, later the male becomes less involved. The breeding season lasts 32-33 days. In a clutch of four, the young hatch within four days. During the breeding season and in the first 10 days of the nestling season, the male almost exclusively supplies the female and later the young with food, which it lays on the edge of the nest. The female only begins to hunt again when the nestlings molt into their first juvenile plumage and are able to cut up prey on their own. It is not clear whether brood aid occurs; in any case, three adult individuals were occasionally observed in a nest with chicks.
Nestling time
After hatching, the chicks are unable to lift their heads; They usually spend the first days of their lives lying down, later sitting down. At around 7 days they can change their position in the nest, at 20 they are in the nest; At this age, they also begin to cut up prey on their own, after having previously been fed bite-sized bites by the female. This is also the time when the female begins to hunt again and the young remain alone for longer periods of time. Aggressive behavior of older chicks towards younger ones occurs, but it is not very pronounced; Fratricide is rare. The training of the flight muscles begins around 30 days; they leave the nest after 38 days at the earliest. The development of the young can be very slow in bad weather, so that the nestling period can last up to 50 days. Although the young birds are able to strike prey on their own shortly after they have fled, they are looked after by the adult birds for at least two weeks.
Dismigration, Breeding Success, and Life Expectancy
After the lead time, young birds often join together to form youth groups, which usually roam around in an undirected manner, but do not move too far from the nest location. Only after a few weeks of vagabonding do they swivel on a south course and start migrating. Young birds from resident populations maintain their nomadic life during the winter months. The species is very faithful to the breeding site: adult birds return to the nest environment for many years, most young birds try to establish their own territory in the nest environment.
Breeding success and escape rate vary considerably from year to year. When the main prey is scarce, king buzzards do not breed at all or reduce the clutch size. In good feeding years, on the other hand, clutches of four and five are not uncommon and, with appropriate weather conditions, the parents often manage to get all the young birds to fly. Overall, the breeding success is not very great due to the weather, lack of food and predation . A study in southern Idaho , which extended over the years 1977-1994, showed a breeding success of only 45.6%, that is, of all broods that started, only about half brought at least one young to fly. However, if only the successful broods are used, the escape rate is quite high with an average of around 2.5 young birds per brood that has started.
About 45% of the young birds do not survive their first year of life. After that, the death curve flattens out very sharply. The average age of newly-ringed birds found nestling was a little over 2 years. The maximum age in the wild is given as 20 years; Captive birds sometimes age.
Systematics
Since the species was first identified in 1838, it has undergone numerous taxonomic changes and was given the names Archibuteo regalis , Buteo californicus , Lagopus ferrugineus , Buteo ferrugineus , Archibuteo ferrugineus and Triorchis ferrugineus . Archibuteo and Triorchis are now obsolete, and the assignment to Buteo is beyond doubt. The first specific epithet ferrugineus was retained in the American common name Ferruginous Hawk.
In 1838 Martin Hinrich Lichtenstein named a wintering specimen of this species from Monterey Falco ferrugineus . In 1922 Erwin Stresemann recognized that Falco ferrugineus was already occupied, because in 1835 Alexander von Nordman had already chosen Falco ferrugineus as the name for the thumb spider ( Accipiter superciliosus ). This made Lichtenstein's rating invalid. The next free, valid name was Archibuteo regalis , a binomial that George Robert Gray had chosen in 1844 for the bellows - also of a hibernator - that came from Real del Monte and was in the British Museum . It is unclear who collected this bellows, but Ferdinand Deppe or William Bullock are suspected . Gray became the first to describe it . Although Buteo ferrugineus was not a valid name, it kept appearing in the literature of the late 19th and early 20th centuries until it was officially introduced in the 4th edition of the American Ornithologists' Union Birdlist (1931).
The family relationships of the species are not fully understood. A molecular genetic study from 2003 shows Buteo lagopus as a sister species, a relationship that was previously suspected due to morphological and behavioral similarities and had led to the establishment of the genus Triorchis . In particular, there is a lack of new work on the relationship between B. regalis and B. hemilasius .
Despite the large range, which is divided into two halves by the continental divide, no subspecies are described.
Persistence and Threat
As of the end of 2019, the population of the royal buzzard is considered safe. (IUCN = LC). The total population in North America is estimated at 110,000 individuals. Overall, the population development is positive with an annual increase of 0.61% (1966 - 2015), but regionally there are also declines in the population. Above all in the mixed grass prairies of the Midwest , stock losses of up to 1.6% were recorded annually. In addition to the different weather and food conditions during the breeding season, the availability of suitable nesting opportunities is a determining variable for the population development. Broods on very elevated structures have significantly better escape rates than broods near the ground. The establishment of nesting platforms is therefore of particular importance for the population development of the species.
Nestlings and young birds in particular are often victims of bad weather periods, lack of food and predation. Bobcats , coyotes , silver badgers and foxes , as well as a number of birds of prey and the Virginia owl hunt nestlings, crows can destroy unguarded clutches. Adult individuals are at risk from parasites and diseases, but increasingly from the destruction of their habitat, as well as from collisions in road traffic and with wind turbines. Regional attempts are being made to control the numbers of pair dogs by shooting and poisoning them; these campaigns have a negative impact on predator populations, both through resulting food shortages and secondary poisoning. The species is very sensitive to disturbances. Increasing leisure tourism, even in remote areas, can lead to the abandonment of breeding territories and the abandonment of nests.
literature
- James Ferguson-Lees , David A. Christie : Raptors of the World . Houghton Mifflin, Boston 2001, ISBN 0-618-12762-3 .
- CM White, P. Boesman and JS Marks, (2019): Ferruginous Hawk (Buteo regalis) . In: Josep del Hoyo , A. Elliott, J. Sargatal, DA Christie, E. de Juana (Eds.): Handbook of the Birds of the World Alive. www.hbw.de, Lynx Edicions, Barcelona. Uploaded from https://www.hbw.com/node/53143 on November 14, 2019.
- J. Ng, MD Giovanni, MJ Bechard, JK Schmutz, and P. Pyle (2017). Ferruginous Hawk (Buteo regalis) , version 2.0. In: The Birds of North America (PG Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.ferhaw.02
- John B. Dunning Jr. (Ed.): CRC Handbook of Avian Body Masses . CRC Press, Boca Raton (Fl) 1992, ISBN 0-8493-4258-9 .
- George Robert Gray: The genera of birds: comprising their generic characters, a notice of the habits of each genus, and an extensive list of species referred to their several genera . tape 1 . Longman, Brown, Green, and Longmans, London 1849, pp. 12 ( digitized version ).
Individual evidence
- ↑ a b c d e f g Handbook of the Bird of the World
- ↑ Handbook of Avian Body Masses . P. 60
- ↑ Editor's note: The information is inconsistent. The HBW calls him the largest buzzard; BNA as the second largest after the highland buzzard. The information from Avian Body Masses also suggests, due to the range of variation in size and weight, that both share first place .
- ↑ a b Raptors of the World. P. 702
- ^ BNA (Birds of North America) Introduction
- ↑ a b c d Raptors of the World. P. 703
- ↑ a b Martin J. Riesing, Luise Kruckenhauser, Anita Gamauf (†) and Elisabeth Haring: Molecular phylogeny of the genus Buteo (Aves: Accipitridae) based on mitochondrial marker sequences . In: Molecular Phylogenetics and Evolution 27 (2003) pp. 328-342. doi: 10.1016 / S1055-7903 (02) 00450-5 Kruckenhauser & Gamauf et al.
- ↑ a b https://www.iucnredlist.org/species/22695970/93535999 IUCN redlist
- ↑ BNA Population Status ~ Numbers
- ↑ a b c d BNA Appearance
- ^ BNA Locomotion
- ↑ a b BNA Molts
- ↑ BNA Vocalizations
- ↑ Voice example - Revierruf
- ↑ Voice example - call near the nest
- ↑ BNA Breeding Range
- ↑ a b BNA Overwintering Range
- ↑ a b BNA Timing an Routes of Migration
- ↑ a b c BNA Habitat in Breeding Range
- ↑ a b c Raptors of the World. P. 704
- ↑ a b BNA Home Range
- ^ BNA Territoriality
- ↑ a b c d BNA Diet - Quantitative Analysis
- ↑ a b BNA Sexual Behavior
- ↑ a b c BNA Breeding - Nest Site
- ↑ a b c d BNA Incubation and Hatching
- ^ BNA Initial Dispersal from Natal Site & Fidelity to Breeding Site and Winter Home Range
- ↑ a b c d e f BNA Demography and Populations
- ^ A b c Neil D. Woffind: History of the Naming of the Ferruginous Hawk : In: The Great Basin Naturalist 59 (3), 1999, pp. 221-229 pdf. engl
- ^ Joseph Grinnell : The two Check-Lists of 1931 - A critical Commentary . In: The Condor 34, No. 2, 1932 p. 88
- ↑ Avibase
- ↑ BNA Systematics - Related Species