African hawk-eagle

The African hawk-eagle is a large bird of prey. Like all eagles, it belongs to the family Accipitridae. This species' feathered legs mark it as a member of the Aquilinae subfamily. The African hawk-eagle breeds in tropical Sub-Saharan Africa. It is a bird of assorted woodland, including both savanna and hilly areas, but they tend to occur in woodland that is typically dry. The species tends to be rare in areas where their preferred habitat type is absent. This species builds a stick nest of around across in a large tree. The clutch is generally one or two eggs. The African hawk-eagle is powerfully built and hunts small to medium-sized mammals and birds predominantly, occasionally taking reptiles and other prey as well. The call is a shrill kluu-kluu-kluu. The African hawk-eagle is listed as Least Concern by the IUCN, but a study in 2024 showed that this species is experiencing a severe population decline of ~91%, suggesting it be listed as critically endangered.

Taxonomy

The African eagle is a member of the Aquilinae or booted eagles. This is a rather monophyletic subfamily of approximately 38 species are classified in the subfamily, all bearing the signature well-feathered tarsi. The Bonelli's eagle was once lumped within the same species as the African hawk-eagle. However, there are several morphological differences between the two species, in addition to discrepancies in life history and their considerably allopatric distribution. Now, the two species are almost universally considered distinct species. Despite the differences between the Bonelli's eagle and the African hawk-eagle the two species are visibly similar and are still considered sister species. Recent DNA research has resulted in the two species being moved, in 2014, to the genus Aquila from Hieraaetus, along with a third possibly related species, the Cassin's hawk-eagle. More specifically and surprisingly, Bonelli's, African hawk- and Cassin's hawk-eagles were found to be genetically closely related to the golden eagle species complex, which also includes Verreaux's eagle, Gurney's eagle and wedge-tailed eagle. These species are all rather larger and morphologically distinct from the Bonelli's and African hawk-eagles and tend to have much more uniform and darker ventral plumages. Furthermore the four other traditional members of the Aquila genus have been revealed to be a separate species complex despite showing superficial similarity to the golden eagle group, i.e. being relatively large and long winged with usually rather uniform and dark colours.

Description

The African hawk-eagle has a somewhat small head but one that protrudes quite well due its quite long neck and relatively prominent beak. Furthermore, the species possesses a longish tail, with long and somewhat slender feathered legs and has large, robust feet. Although African hawk-eagles occasionally take to perching in the open, they usually are somewhat obscured for much of the day within the cover of foliage and often perch relatively low down in tall trees. The wing tips tend to fall a bit short of the tail tip. The adult African hawk-eagle evidences a fairly pied look with slate black-grey coloration above and whitish coloration below. At a distance, they may appear purely black-and-white but at close range they show sparse but extensive white flecks on the mantle and wing coverts. Occasionally, a greyer patch may be apparent on the folded secondaries of perched or sitting birds. The tail of an adult is grey with thin dark bars, a broad subterminal band and a white tail tip. The adult hawk-eagle's underside is white with bold but small and sparse drop-like blackish streaks. As was noted in a 2010 study, in a usual instance of plumage sexual dimorphism for an Aquilinae eagle, the underside tends to more sparsely marked on adult males and more densely marked on adult females to such a degree that an experienced observer may be able to sex individual African hawk-eagles despite the two sexes being similar in size. The adult African hawk-eagles has whitish coloring on the thighs and the crissum. The juvenile of the species is highly distinct from older hawk-eagles. Juveniles are moderately dark brown above with some pale edging, a slightly black-streaked head and a more clearly barred tail than adult hawk-eagles. The underside has a tawny-rufous base colour. When juvenile African hawk-eagles present black shaft streaks below they are usually only obvious on the flanks and they can border on being absent. Once developing as an immature at two to four years old, the upperside becomes progressively darker, the underside paler and more streaked and a subterminal tail band forms. At four years of age, as in related species, the African hawk-eagle becomes fully mature. The eyes of adult hawk-eagles are rich yellow while those of juveniles are hazel-brown while the cere and feet at all ages range from dull to somewhat brighter yellow.
In flight, the African hawk-eagle appears as a mid-sized raptor with a rather small but well-protruding head, a longish tail and wings that are neither particularly long nor broad. The species tends to flight with powerful and shallow beats. When gliding or soaring, their wings tend to be well-spread and, when engaging a glide, their carpal points tend to be only slightly forward pressed. Adult African hawk-eagle possess on the upperside of their wings a significant pale whitish-grey window on the base of their primaries, extending into dark grey panels across the black-tipped secondaries. The grey tail usually only shows obscure bars from a distance besides the broad subterminal band. From below, the black trailing edges with contrasting greyish white flight feathers as well as the more apparent subterminal band are in both cases distinctly abutted by paler grey feathering. The greater coverts show various solid black diagonal markings that coalesce and create a signature appearance from below in a flying adult African hawk-eagle. In flying juveniles, if seen from above, the contrasting creamy window, as in the adults, and barred tail stand out as the most distinct features of the species. Below, the juvenile African hawk-eagles show rufous wing linings that match the forebody and rather varying dusky edges, which often form carpal arcs and sometimes continuing as wing diagonals. The wings are otherwise rather nondescript in juvenile African hawk-eagles with greyish buff secondaries and tail thinly barred and white-based primaries.

Size

The African hawk-eagle is a small-to-mid-sized eagle and a fairly large raptor. Despite its relatively modest size, this species can appear surprisingly large when perched or standing on the ground due in no small part to its long neck, long legs and rather upright posture. The sexes are rather similar in size for a bird of prey, but the females, in the expected sexual dimorphism, averages about 5% about larger and up to 20% heavier. On the other hand, there is reportedly little overall discrepancy in their foot size or particularly in talon size. In total length, African hawk-eagles may vary in length from, with some of the largest females sometimes reported to measure to as much as . Mean length of a male may be around while the mean length of a female may be around. Wingspan among this species may vary from. Body mass in males can vary from while the body mass of females can vary from. In one sample, 14 males were found to have averaged while a sample of 10 males averaged. In same datasets, 7 females averaged and 10 females averaged. A sample of 36 unsexed African hawk-eagles in southern Africa averaged in wingspan while an accompanying sample of 21 unsexed specimens averaged in body mass. Among standard measurements, the wing chord of males measures from while that of females is from. African hawk-eagles measure in tail length from and, in a limited sample, in tarsus length from. In Kenya, mean wing chord length of unsexed hawk-eagles was, mean tail length was, mean culmen length was and the hallux claw, the enlarged rear toe talon that is used as the primary killing apparatus on accipitrid raptors, measured a mean of, measuring from in different specimens. The talon size is extremely large for this raptor's size, being similar to that of some eagles that are around twice as heavy such as eastern imperial eagles.

Identification

The African hawk-eagle is largely allopatric from the most similar extant species of eagle, its sister species, the Bonelli's eagle. However, they may need to be distinguished in the Red Sea area, where minimal range overlap occurs. The Bonelli's eagle is larger and relatively broader-headed, shorter-necked, with proportionately longer wings and a shorter tail. The adult Bonelli's is much lighter and browner dorsally with usually a white patch on the mantle but no paler wing panels above. The Bonelli's eagle tends to be less contrastingly marked below, being rather creamy and lacking strong markings. The juvenile Bonelli's is a bit more similar to the juvenile African hawk-eagle but can be told apart by proportions and by being paler backed and again lacks the clear "windows" of the juvenile hawk-eagle. There are a few other largely black dorsally and white ventrally largish raptors in sub-Saharan Africa but the African hawk-eagle is the largest and comes the closest to being typically aquiline in bearing and morphology. One species sometimes considered rather similar is the adult Ayres's hawk-eagle but that hawk-eagle is smaller, more compact as well as being rounder headed. The Ayres's may show a nuchal crest and also lacks the windows seen on the wing upperside and is more evenly blotched or streaked all over the underbody, wing linings and legs. Additionally, the Ayres's hawk-eagle is less heavily darkly marked on the wings, being more spotted and splotched with black, lacking black trailing wing edges as well as the subterminal tail band of the African. Juvenile Ayres's can be similar in flight below to the juvenile African hawk-eagle but is usually paler rufous with darker quills and is generally much paler above with whitish scaling and rufous crown and mantle. Moreover, in all plumages, the Ayres's show white "landing lights", reminiscent of a booted eagle. Other raptors of a pied pattern vaguely reminiscent of the African hawk-eagle in Africa, such as the black sparrowhawk, the augur buzzard and the Cassin's hawk eagle, are fairly obviously distinct in appearance and proportions as well as habitat. Of these three, the adult Cassin's is by far the most similar in structure and appearance to the African hawk-eagle but the two are mostly allopatric in distribution, with the Cassin's typically dwells in mature forests unlike the sparser, drier wooded-savanna habitats of the African hawk-eagle. Compared to the Cassin's hawk-eagle, the African species is larger, shorted tailed and much longer winged, with a much more heavily marked underbody, denser black about the mid-wings and barely barred quills. At a distance, the African hawk-eagle's flight profile can recall that of the European honey-buzzard but the head is even smaller in that species. Furthermore, the wing actions and patterning of this smaller Palearctic migrant is highly different, therefore confusion with the honey-buzzard is quite unlikely. Even more unlikely to be confused with the African hawk-eagles even at a distance is the far larger and bulkier crowned eagle, which is highly distinct in colour and has relatively shorter but much broader wings. One other species that may be need to be distinguished in distant flight, this time from the juvenile African hawk-eagle, is the juvenile booted eagle. That species is smaller but proportionately much longer winged and shorter tailed than the juvenile African hawk-eagle. Furthermore, the booted species is barred on the tail and has completely different underwing pattern.