The African hawk-eagle (Aquila spilogaster) is a formidable bird of prey that graces the skies of tropical Sub-Saharan Africa. As a member of the Accipitridae family, it shares kinship with all eagles, distinguished by its feathered legs that classify it within the Aquilinae subfamily.
This eagle thrives in diverse woodland environments, encompassing both savanna and hilly terrains, with a preference for drier woodlands. Its presence is notably scarce in regions devoid of its preferred habitat.
Taxonomy and Evolution
The African hawk-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 (Aquila fasciata) was once lumped within the same species as the African hawk-eagle. 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 (Aquila africana). More specifically and surprisingly, Bonelli's, African hawk- and Cassin's hawk-eagles were found to be genetically closely related to the golden eagle (Aquila chrysaetos) species complex, which also includes Verreaux's eagle (Aquila verreauxii), Gurney's eagle (Aquila gurneyi) and wedge-tailed eagle (Aquila audax).
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Physical Characteristics
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 genders 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.
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A juvenile African hawk-eagle.
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.
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 reverse 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.
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Size and Weight
In total length, African hawk-eagles may vary in length from 55 to 68 cm (22 to 27 in), with some of the largest females measuring to as much as 74 cm (29 in). Mean length of a male may be around 60 cm (24 in) while the mean length of a female may be around 65 cm (26 in). Wingspan among this species may vary from 130 to 160 cm (4 ft 3 in to 5 ft 3 in). Body mass in males can vary from 1,250 to 1,750 g (2.76 to 3.86 lb) while the body mass of females can vary from 1,480 to 2,470 g (3.26 to 5.45 lb).
Here's a table summarizing the key measurements:
| Measurement | Males | Females |
|---|---|---|
| Length | 55-68 cm (avg. 60 cm) | 65-74 cm (avg. 65 cm) |
| Wingspan | 130-160 cm | |
| Weight | 1,250-1,750 g | 1,480-2,470 g |
Among standard measurements, the wing chord of males measures from 412 to 446 mm (16.2 to 17.6 in) while that of females is from 435 to 465 mm (17.1 to 18.3 in). African hawk-eagles measure in tail length from 225 to 290 mm (8.9 to 11.4 in) and, in a limited sample, in tarsus length from 90 to 100 mm (3.5 to 3.9 in). In Kenya, mean wing chord length of unsexed hawk-eagles was 433 mm (17.0 in), mean tail length was 253 mm (10.0 in), mean culmen length was 32.3 mm (1.27 in) and the hallux claw, the enlarged rear toe talon that is used as the primary killing apparatus on accipitrid raptors, measured a mean of 38 mm (1.5 in), measuring from 32.6 to 41 mm (1.28 to 1.61 in) 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 (Aquila heliaca).
Identification and Similar Species
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 (Hieraaetus ayresii) 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 (Hieraaetus pennatus).
Other raptors of a pied pattern vaguely reminiscent of the African hawk-eagle in Africa, such as the black sparrowhawk (Accipiter melanoleucus), the augur buzzard (Buteo augur) and the Cassin's hawk eagle (Aquila africana), 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 (Pernis apivorus) 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 (Stephanoaetus coronatus), 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.
Vocalization
The African hawk-eagle is generally silent outside breeding season. Its main call is melodious fluting klooee. The call is perhaps most often recorded in contact between pair members. The call is sometimes considered not unlike that of the often sympatric Wahlberg's eagle (Hieraaetus wahlbergi) but that of the African hawk-eagle tends to be less drawn out and more mellow in tone. The main call may be repeated or develop into klu-klu-klu-kleeee or kluu-kluu-kluu with variations.
This extended call may be given both during courtship and in moments of aggression, such as when driving away other raptors near their nest. Often, African hawk-eagles call on near nest including repeated kweeooo or ko-ko-kweroo, which seemed to be repeated during nest construction and repair. A farther variation, a kwaak, may be made by both of a pair when they are excited near the nest. A squealing skweeyra call by the female is a probable food solicitation call when she sees the male. They also make softer "conversational" sounds.
Distribution and Habitat
The African hawk-eagle is found across much of sub-Saharan Africa. The farthest north the species ranges is in eastern Eritrea and adjacent areas of Ethiopia, after a substantial gap, the range resumes almost throughout southern Ethiopia. The African hawk-eagle tends to be scarce to rare in West Africa with much study of the details due to their local extreme scarcity. Here the species may be found into southern Senegal, The Gambia, Guinea-Bissau, eastern Guinea, northernmost Sierra Leone, Cote d’Ivoire, Burkina Faso, the northern portions of Ghana, Togo and Benin and north-central Nigeria.
In central and East Africa, the range of the African hawk-eagle includes southern Chad, southern Sudan, where they tend to be fairly rare, South Sudan, west Somalia, the central and southern portions of the Democratic Republic of the Congo and essentially all of Uganda, Kenya and Tanzania. This species is found throughout the northern nations (within favorable habitats) of southern Africa including Angola, Zambia, Mozambique, Malawi, Zimbabwe, north-central Namibia, northern and eastern Botswana and northeastern South Africa, north of the Orange River. The species is gone or nearly so from Eswatini, with the last confirmed breeding having been in 2002.
This is a bird of well-wooded countryside. This species tends to favor tropical broadleaf woodland and woodland edge within the savanna but does not tend to occur in true deep forest. Additionally, African hawk-eagles can adapt to thornbush areas such as the veld but tends to occur moreso within riparian zones, which tend to permit the growth of strips of taller trees. Miombo and especially Mopane woodland may be central to the existence of the species in southern Africa.
Behavior and Hunting Techniques
The African hawk-eagle is uncommonly aggressive and bold predator. Their primary hunting tool is their powerful feet. In general, their sneaky foraging techniques recall a huge Accipiter. In terms of agility and hunting prowess, especially in terms of their short-distance flight after prey, they are also somewhat reminiscent of an Accipiter.
Mostly the African hawk-eagle engages in still-hunting, wherein they scan from prey from an inconspicuous perch for a long period. When prey is spotted, the hawk-eagle engages in a low level dash from their perch in cover. They often uses cover to cloak their approach almost up the point where they strike. While it has been claimed that their flight is “silent”, it would presumably be more correct to say that the hunting hawk-eagle engages in minimal flapping flight so as to not alert prey to their approach.
Often, the hawk-eagles wait near prey-concentrated areas, such as waterholes and among riparian trees for birds to come to drink or by clearings that birds frequently cross. African hawk-eagles may too quarter above the ground and seize any prey they surprise. They are capable of sometimes taking birds on the wing but usually prefer to catch them on the ground and may force avian prey intercepted in the air back to the ground. Often terrestrial birds are taken right around the moment they alight. In some instances, prey may be chased, even on foot, into thickets.
African Hawk-Eagle in Flight.
Diet
The typical prey of African hawk-eagles tends to be medium to large-sized birds and small-to-medium-sized mammals. Less usual prey can include reptiles and insects. As much as 74-86% of the diet can be birds and as much as 54-70% of the diet can be mammals. In general, due to a combination of factors such as their usual practice of keeping their nest area clean and their tendency to often evade researchers' notice due to hidden perch sites, the diet of African hawk-eagles is less well-known than that of larger African eagles or the Bonelli's eagles (especially in Europe). However, what is known suggests that this is an exceptionally powerful predator that may nearly rival much larger eagles such as martial eagles (Polemaetus bellicosus) in its ability to take large and middle-sized prey. A general picture has emerged that the African hawk-eagle is highly opportunistic and takes any variety of appropriately sized prey as it becomes available.
Nesting and Reproduction
This species builds a stick nest of around 1 m (3.3 ft) across in a large tree. The clutch is generally one or two eggs. The African hawk-eagle usually lays 2 eggs. Sometimes, they lay 1 or 3 eggs. In Zambia, about half of the nests had one egg, and the rest had two. In Malawi, 80% of nests had two eggs. The eggs are chalky white with varied markings, from speckled with dull red to mostly plain. They measure about 59.5 to 75.2 millimeters (2.3 to 3 inches) tall and 46 to 55.7 millimeters (1.8 to 2.2 inches) wide.
The nest is a very large, platform-like structure made of sticks. It's usually built in the main fork of a large tree or far out on a strong branch. Nests are typically 4 to 36 meters (13 to 118 feet) above the ground, often between 9 and 13 meters (30 and 43 feet). Common trees used for nests include Acacia, Adansonia, Khaya, Terminalia, and even non-native Eucalyptus. Nests are often found near rivers.
Incubation takes 43-44 days, and the eggs are incubated by both parents. the one chick is cared for if multiple eggs hatch, due to siblicide (also known as Cainism, where the older chick kills the younger). Fledging (leaving the nest for the first time) happens between 60 and 70 days of age. After leaving the nest, young eagles stay with their parents for about 3 to 4 weeks.
Nest of an African Hawk-Eagle.
The African Hawk Eagle (Aquila spilogastra) catching pheasant
Conservation Status and Threats
African Hawk Eagles are currently listed as Least Concern by BirdLife International. Though the African Hawk-eagle is widespread throughout its range, that doesn't mean it isn't facing some very serious threats. For example, because this raptor will sometimes feed on domestic chickens and other fowl, farmers will shoot them. As woodland trees are cut down, these birds are also losing important habitat. Sadly, researchers have even found some individuals that have drowned in farm reservoirs. Over the past few decades, they have become scarce to rare outside of protected areas across Africa.
How the Peregrine Fund is Helping
Peregrine Fund biologists are studying African Hawk-eagles to better understand the causes for their decline across the continent of Africa. At present, we are GPS tracking the movements of five hawk-eagles in Kenya, as well as studying their reproductive rates. Through environmental education efforts, we are also working to put a stop to the common practice of poisoning carcasses to kill large predators, which also kills a host of wildlife including vultures, eagles, and other scavenging birds. These efforts will certainly benefit all raptors of the region, including the African Hawk-eagle.
