Crowned eagle
The crowned eagle, also known as the African crowned eagle or the crowned hawk-eagle, is a large bird of prey found in sub-Saharan Africa; in Southern Africa, it is restricted to more easterly areas. Its preferred habitats are principally riparian woodlands and various forests. The crowned eagle is the only extant member of the genus Stephanoaetus. A second species, the Malagasy crowned eagle, went extinct after early humans settled on Madagascar.
Mammals comprise the majority of the eagle's diet. Principal prey species vary throughout its large range, with monkeys, antelopes, rodents, hyraxes, and viverrids all being notable prey groups. Other wild mammals recorded as prey include bushpigs, pangolins, and bats. Birds are also a considerable component of the diet in some populations. In an urban population in Durban, South Africa, camera traps at nest sites revealed that 25% of prey items were birds, of which 17% were hadada ibis juveniles. In Taï, Côte d'Ivoire, trumpeter hornbills comprised 8% of prey. Reptiles and carrion are occasionally consumed. Domesticated cats, dogs, sheep, goats, and chickens are sometimes taken. However, in Durban, South Africa, domesticated animals comprised only 6% of the diet across 11 nests and 836 prey items, of which 3% were chickens. There is at least one credible report of an attack, presumably a case of attempted predation, on a 19.6 kg human child.
Although the crowned eagle's long tail imparts an overall length of up to, it is lighter by weight, and has a considerably shorter wingspan, than Africa's largest eagle, the martial eagle. It is, nevertheless, considered Africa's most powerful eagle with respect to its prey's body size. It has been known to prey on ungulates as large as bushbuck, which can weigh up to, albeit usually much less. The crowned eagle possesses unusually large talons and strong legs, and may kill by simply crushing prey's skull. The eagle is also bold and ferocious; records documented from beneath a nest show the remains of a large male sooty mangabey weighing.
Due to their ecological and behavioral similarities, the crowned eagle is considered to be the African counterpart of the Central and South American harpy eagle. Thanks to its bold and highly conspicuous behavior, it is exceptionally well-studied for a large, forest-dwelling eagle. Due to a relatively high level of habitat adaptability, it was until recently considered to be faring well by the standards of large, forest-dependent raptors. However, today it is generally thought that it is decreasing far more than was previously perceived due to the almost epidemic destruction of native tropical African forest. It is now listed by the IUCN as Near Threatened.
Taxonomy and systematics
This species was first described by Carl Linnaeus in the 12th edition of Systema Naturae, published in 1766, as Falco coronatus. Since birds were grouped largely on superficial characteristics at that time, many unrelated species were grouped by Linnaeus in the genus Falco. The actual taxonomic alignment of the crowned eagle is apparent due to its feathering over its tarsus, which is generally rare in unrelated accipitrids. The crowned eagle is actually part of the diverse "booted eagle" group, which has sometimes been considered a distinct subfamily. Included in this grouping are the genus Aquila and all species described as "hawk eagles" including the genera Spizaetus and Nisaetus. Other assorted monotypical genera included amongst "booted eagles" are Lophaetus, Polemaetus, Lophotriorchis and Ictinaetus.At one time, the genus Stephanoaetus was considered a "specialized offshoot" of the Spizaetus hawk-eagles based on morphological attributes. DNA sequences utilizing one mitochondrial and three nuclear genes indicated the crowned eagle is a sister species to the Asian hawk-eagles, which are now considered a separate genus, Nisaetus, that are not closely related to the neotropical hawk-eagles, which are retained in Spizaetus. However, another recent study, this time of sequences of two mitochondrial and one nuclear genes, did not reveal a close relationship of this eagle to any other accipitrid, including the Nisaetus species, and the genus was found to be genetically highly divergent from other "booted" eagles". In a case of convergent evolution, the much heavier harpy eagle, which is outside of the "booted eagle" group, has a similar skeletal morphology to the crowned eagle. Two less well-known, probably distantly related species, the mountain hawk-eagle and the black-and-chestnut eagle, have also been found comparable to the crowned eagle. While both are slimmer and smaller, these eagles are also large-bodied, strong-footed offshoots of the evolutionary radiation of forest-dwelling booted eagles, respectively distributed in East Asia and South America. The adult crowned eagle even has somewhat intermediate appearance between these birds, sharing the variable patterning of the mountain hawk-eagle and some of the colouring of the black-and-chestnut.
Until possibly up to 1500, another crowned eagle species, the Malagasy crowned eagle existed. Similar in size and form to the extant crowned eagle, the Malagasy crowned eagle probably filled a similar niche in Madagascar, but was likely to have preyed on lemurs in place of monkeys. Apparently, the Malagasy crowned eagle became extinct due mainly to the loss of prey and habitat change, attributable to early humans on the island. To date, the living crowned eagle has no recognized subspecies. However, Simon Thomsett noted from field experience possible racial differences between crowned eagles in limited woodland habitats in East and South Africa, which have historically been the main populations studied, and those that live in denser West African rainforest, in the central part of the species distribution. The latter population, he noted, appeared smaller but relatively larger footed, seemed chestier in build and appeared to have deeper eyebrows than the bush eagle; behaviorally the rainforest eagles seemed bolder and louder, which is reinforced in other accounts of the species.
Distribution
The crowned eagle is found only on the continent of Africa. In East Africa, the crowned eagle's range extends from central Ethiopia, to Uganda, forested parts of Kenya and Tanzania to as far south as eastern South Africa, with a southern distribution limit around Knysna. In western and central Africa, the crowned eagle's range extends through much of the vast African rainforest. They may be found from Senegal, The Gambia, Sierra Leone and Cameroon, where they inhabit the Guinean forests, to the Democratic Republic of the Congo, where they live in the Congolian forests, and down south to as far Angola. Despite its large distribution there, the crowned eagle is now rare in many parts of West Africa.Description
The crowned eagle is a very large eagle. Measuring from in length, it is the fifth longest extant eagle in the world. The female, at a weight of, is around 10–15% larger than the male, at a weight of. An average body mass of was given in one account. Elsewhere, an average of has been claimed. Slightly smaller weights were found in a South African survey where 5 males averaged and 8 females averaged. Overall, they are the 9th heaviest living eagle species. The wingspan typically ranges from. The largest authenticated wingspan for a female was, with a claim of wingspans of up to needing confirmation. This eagle's wingspan is quite short for the bird's size, being around the same mean width as that of a tawny eagle or a short-toed snake eagle, species that weigh about half as much as a crowned eagle. However, the somewhat boxy and rounded wings are quite broad, being broader than, for example, the much longer-winged golden eagle. The wing morphology of the species gives it maneuverability in its densely wooded environment. The wing chord measures, with a median of in males and in females. In South Africa, 5 males averaged in wing chord length and 7 females averaged. While it, on average, is less heavy and has a smaller wingspan than the often sympatric martial eagle, its average total length exceeds that of the martial eagle thanks to its much longer tail. The crowned eagle's tail is from long, with a median of in males and in females. South African males averaged in tail length in a sample of 4 and females averaged. The bill is of a medium size relative to its body size, with one large museum specimen's bill measuring in length from the gape, in culmen length and in bill depth. In South Africa, culmen length averaged in 4 males and in 7 females, with a range in both.The tarsus is of a modest length for a raptor of its size, at, and is clearly shorter than that of martial eagle. However, the feet and legs are visibly thicker and heavier than those of the martial eagle and the talons are apparently quite massive in both length and width. While few comprehensive measurements of the talon size of wild crowned eagles are known, one female museum specimen reportedly had a hallux-claw of, while another female was measured at 5 years of age, the age of sexual maturity, in the hallux-claw and an adult male measured. In South Africa, hallux-claw length averaged in 5 males and in 7 females with a range in both of. These figures put their talon size as around the same size as the largest golden eagles and half the size of a harpy eagle. Some captive crowned eagles have been credited with a hallux-claw length of up to, although, much like a single report of captive harpy eagles with a hallux-claw, no such outsized talons are known to have been confirmed. In a small sampling of large, forest-dwelling raptors, the front-left talon of the crowned eagle, at, was around one cm less than that of a harpy eagle or the huge, recently extinct Haast's eagle and slightly smaller than those of the Philippine eagle. Considering a big female of these species can weigh up to twice as much as an average crowned eagle may illustrate the relative largeness of the crowned eagle's talons.
The adult crowned eagle is quite strikingly plumaged. Its crown is dark to rufous-tinged brown with a prominent, oft-raised black-tipped double crest, which can give the head a somewhat triangular appearance. The upperparts of an adult are a blackish brown-grey color, with a variable tinge of blue. The throat is brown while the belly and breast are white overlaid densely with blackish bars and blotches, variably marked with cream or rich buff-rufous coloration. The wing primaries are white at the base, broadly tipped with black and crossed by two black bars. The tail is black with brownish-grey bands. The thighs and legs are barred and closely spotted with black and white. The underwing coverts of adults have a bold chestnut coloration, spotted lightly with black. The adult crowned eagle has eyes that can range from yellow to almost white, a cere and feet of an ochre-yellow color and black talons. In the wild, misidentification of an adult is improbable thanks to the species' bearing and voice. The strongly barred outer wings and tail are all diagnostic in flight. Further simplifying identification, details such as the crest, the bird's upright perching posture and large size are unique to this animal. While they do differ somewhat in size, the sexes' dimorphism by size is relatively modest and eagles are unlikely to be sexed by this alone. However, the male may be distinguished by his more rapid wing beats from the more sluggish female.
As seen in about half of the "booted eagle" group, the juvenile crowned eagle has strikingly different looking plumage compared to the adults. Much variation occurs as the maturation process occurs. A great majority of juveniles have a white head and underside, which contrast with the thighs and legs, which are heavily spotted with black. The juvenile eagle's back is light brown or grayish-brown, with pale feather edgings that often give the back a scaled appearance, especially on the upper-wing coverts. There is often a pinkish red wash on the upper chest. Just-fledged chicks tend have dark patched faces, freckled bibs and slightly barred chests and spotted legs. Less common juvenile crowned eagle plumages, possible even when they are under a year of age and still under parental care, may include eagles so stripy that they which one could easily have aged as two- to three-year-olds. The tail of the juvenile is black with three pale bars and a narrow black tip. The juvenile eagle's cere is grey and the feet are dull yellow. By 4 months post-fledgling, the inner thighs, previously poorly covered with downy type feathers, are covered with small feathers. While the pale 'morph' young just prior to leaving the nest usually have unmarked tarsus, they soon get spots on the front part of the tibio tarsal joint. The tibio tarsal pad is still bare and obvious up until it is a year old, whereupon it vanishes only to return to incubating females. Eye color is variable too with some having khaki light brown just prior to fledging and others with adult-like yellow ochre eyes. Up to 15 months after leaving the nest, the immature eagles more closely resemble the plumage they have at first independence than the adult's plumage. The juvenile may be confused with the similarly colored juvenile martial eagle, especially in flight. It is distinguished from the martial species in having a much longer, more heavily barred tail, much shorter wings and spotted thighs.