Verreaux's eagle (; Aquila verreauxii) is a large, mostly African, bird of prey. It is also called the black eagle, especially in southern Africa, not to be confused with the black eagle (Ictinaetus malayensis) of south and southeast Asia. The Verreaux's eagle lives in hilly and mountainous regions of southern and eastern Africa (extending marginally into Chad, Mali and Niger), and very locally in the Middle East.
Verreaux's eagle is one of the most specialized species of accipitrid in the world, with its distribution and life history revolving around its favorite prey species, the rock hyraxes. When hyrax populations decline, the species have been shown to survive with mixed success on other prey, such as small antelopes, gamebirds, hares, monkeys and other assorted vertebrates. Despite a high degree of specialization, Verreaux's eagle has, from a conservation standpoint, been faring relatively well in historic times. One population of this species, in the Matobo Hills of Zimbabwe, is arguably the best studied eagle population in the world, having been subject to continuous detailed study since the late 1950s. Like all eagles, this species belongs to the taxonomic order Accipitriformes (formerly included in Falconiformes) and the family Accipitridae, which may be referred to colloquially as accipitrids or raptors.
Taxonomy
This species was first described by René Primevère Lesson in his 1830 publication, Centurie zoologique, ou choix d'animaux rares, nouveaux ou imparfaitement connus, as Aquila Verreauxii.Kemp, A. C. (1994) IN del Hoyo, Elliott & Sargatal. eds. (1994). Handbook of the Birds of the World, vol. 2. The species' name commemorates the French naturalist Jules Verreaux, who visited southern Africa in the early 19th century and collected the type specimen for the French Academy of Sciences.Gargett, p. 30.Mearns, Barbara; & Mearns, Richard. (1988). Biographies for Birdwatchers. The lives of those commemorated in Western Palaearctic bird names. Academic Press: London.
Verreaux's eagle is part of a broad group of raptors called "booted eagles" which are defined by the feature that all included species have feathering over their tarsus, whereas most other accipitrids have bare legs. Included in this group are all species described as "hawk eagles" including the genera Spizaetus and Nisaetus, as well as assorted monotypical genera such as Oroaetus, Lophaetus, Stephanoaetus, Polemaetus, Lophotriorchis and Ictinaetus. The genus Aquila is distributed across every continent but for South America and Antarctica. Up to 20 species have been classified in the genus but the taxonomic placement of some of the traditionally included species has recently been questioned. Traditionally, the Aquila eagles have been grouped superficially as largish, mainly brownish or dark-colored booted eagles that vary little in transition from their juvenile to their adult plumages.
Genetic research has recently shown the Verreaux's eagle is included in a clade with its nearest relatives, the sister species Bonelli's eagle (A. fasciatus) and African hawk-eagle (A. spilogaster), as well as the golden eagle. More distantly related are the sister species pair, the wedge-tailed eagle (A. audax) and Gurney's eagle (A. gurneyi). Closely related to this clade are the Cassin's hawk-eagle (A. africanus). Some of the relationships within this group have long been suspected based on morphological similarities among the large-bodied species.Eagles, Hawks and Falcons of the World by Leslie Brown & Dean Amadon. The Wellfleet Press (1986), . The identification of the smaller, much paler-bellied A. fasciatus and A. spilogaster as members of the clade was a surprise, given that they were previously included in the genus Hieraaetus. Cassin's hawk-eagle has been assigned to both the Hieraaetus group and the Spizaetus/Nisaetus "hawk-eagle" group but is now known based on this genetic data to also nest within Aquila.
Other largish Aquila species, the eastern imperial eagle (A. heliaca), the Spanish imperial eagle (A. adaberti), the tawny eagle (A. rapax) and the steppe eagles (A. nipalensis), are now thought to be a separate, close-knit clade, which attained some characteristics similar to those of the prior clade via convergent evolution. Genetically, the "spotted eagles" (C. pomarina, C. hastata & C. clanga), have been discovered to be more closely related to the long-crested eagle (Lophaetus occipitalis) and the black eagle, and have been transferred to the genus Clanga. The genus Hieraaetus, traditionally including the booted eagle (H. pennatus), little eagle (H. morphnoides) and Ayres's hawk-eagle (H. ayresii), consists of much smaller species, that are in fact the smallest birds called eagles outside of the unrelated Spilornis serpent-eagle genus. This genus has recently been eliminated by many authorities and is now occasionally also included in Aquila, although not all ornithological unions have followed this suit in this re-classification. The small-bodied Wahlberg's eagle (H. wahlbergi) has been traditionally considered an Aquila species due to its lack of change from juvenile to adult plumage and brownish color but it is actually genetically aligned to the Hieraaetus lineage.
Description
Verreaux's eagle is a very large eagle. It measures long from the bill to the tip of the tail, making it the sixth longest eagle in the world.Raptors of the World by Ferguson-Lees, Christie, Franklin, Mead & Burton. Houghton Mifflin (2001), . Males can weigh and the larger females weigh . The average weight is approximately , based on the weights of 21 eagles of both sexes. Other reported mean body mass measurements of Verreaux's eagles were lower however, with seven unsexed birds averaging , while four unsexed eagles in an additional study averaged . In yet another study, seven males were found to average and seven females to average . In another group of weighed eagles, four females were found to average . It is the seventh or eighth heaviest living eagle in the world. In average mass and overall weight range, if not linear measurements, the Verreaux's is very similar in size to its occasional competitor, the martial eagle, which is regularly titled the largest of the African eagles. It also rivals the martial and golden eagles as the largest extant member of the "booted eagle" clan.CRC Handbook of Avian Body Masses, 2nd Edition by John B. Dunning Jr. (Editor). CRC Press (2008), .Brown, L. H., Gargett, V., & Steyn, P. (1977). Breeding success in some African eagles related to theories about sibling aggression and its effects. Ostrich, 48(3-4), 65-71.Mendelsohn, J. M., Kemp, A. C., Biggs, H. C., Biggs, R., & Brown, C. J. (1989). Wing areas, wing loadings and wing spans of 66 species of African raptors. Ostrich, 60(1), 35-42.Biggs, H.C., Kemp, A.C., Mendelsohn, H.P. & Mendelsohn, J.M. (1979). Weights of South African Raptors and Owls. Durban Museum Novitates, 12: 73-81.Brough, T. (1983). Average weights of birds. Ministry of Agriculture, Fisheries and Food, Agricultural Science Service, Aviation Bird Unit, Worplesdon Laboratory.Parry, S. J. (2001). The booted eagles (Aves: Accipitridae): perspectives in evolutionary biology. University of London, University College London (United Kingdom). It has a wingspan of . The wing chord of the male is and that of the female is . Among other standard measurements in the Verreaux's eagles, both sexes measure in tail length and in tarsus length. Other than the female's slight size advantage, adult males and females are physically indistinguishable from each other. Adult Verreaux's eagles are mostly jet-black in color. The yellow coloration of the cere (the bill is gun-metal grey), eye-ring and "eye-brows", all stand out in contrast to the black plumage. Even more prominent on flying birds when seen from above is the white on the back, rump and upper-tail coverts and part of the scapulars, which forms a V-shaped patch, although this feature is partially obscured in perched birds. Adults also have conspicuous white windows on the wing quills at the carpal joint (at the base of the primaries) when seen flying both from above and below. The bill is stout, the head is prominent on the relatively long neck and the legs are fully feathered.
Juvenile and immature plumages differ markedly from the plumage of adults. They are overall a dark brown color. Immatures have a strongly contrasting golden crown and a rufous or ginger nape and mantle. They have small white streaks on the forehead and black on their cheeks. The throat is dark streaked, the lower throat is pale brown and the upper-chest is brown. The rest of the underside is brown but for a blackish-blotched rufous to cream-colored abdomen and lightly marked creamy thighs and legs. The feathers of the upper-tail and upper-wing coverts are brown with white streaks in young birds, while the other tail and wing quills are nearly black. The wing quills when seen from below in flight show considerable whitish mottling, with more extensive white than is typically seen in adult plumages. The immature has a dark brown iris and yellowish feet. Black feathers increase from 2 to 5 years of age amongst a scattering of brown-tipped feathers, though the contrasting creamy trousers are maintained through the 3rd year. By the 4th year, they look dark grey-brown with a buff-patch on the nape and mottling of retained brownish feathers. At the end of the subadult phase at around 5 years of age, the plumage is practically indistinguishable from the adult.Brown, L. 1976. Eagles of the World. David and Charles, . Full adult plumage is probably attained in 5 to 6 years.
The Verreaux's eagle is essentially unmistakable, especially in adulthood. No other black-colored raptor in its range approaches this species' large size, nor possesses its distinctive patterns of white. The golden eagle is of similar size or marginally larger size and the two species are the heaviest living Aquila species and measure only marginally less than the slightly lighter-weight Australasian wedge-tailed eagle in total wing and bill-to-tail length. While the juvenile Verreaux's eagle is quite different from the adult's, its plumage is no less distinctive. No other accipitrid shares the mottled brownish body, blackish wings with large white patches or contrasting whitish, rufous and golden color around the head and neck. The flight profile of Verreaux's eagle is also distinctive: it is the only Aquila species other than the golden eagle to soar in a pronounced dihedral, with the wings held slightly above the back and primaries upturned at the tip to make a V shape. In the Bale Mountains of Ethiopia and possibly in some parts of the Arabian Peninsula and the southwestern edge of the Middle East, the ranges of the golden and Verreaux's eagles overlap, but the golden is a mostly brown bird and shares none of the Verreaux's black plumage. The immature golden eagle has white patches on its underwing as do Verreaux's, but they are less extensive than those of the latter species. The wing shape also differs from the golden's, as the Verreaux's eagle has very broad outer secondaries and a relatively narrow pinch at the base of the primaries, whereas the tapering of a golden eagle's wing is more gradual. The Verreaux's eagle wings have variously been described as paddle, spoon or leaf shaped. Imperial eagles too have white markings on their wing coverts, but are different in flight profile (flatter winged) and overall coloration (dark brown).
Voice