Kronenadler

Bestimmung

The crowned eagle is a very large eagle. Measuring from 80 to 99 cm (31 to 39 in) in length, it is the fifth longest extant eagle in the world. The female, at a weight of 3.2–4.7 kg (7.1–10.4 lb), is around 10–15% larger than the male, at a weight of 2.55–4.12 kg (5.6–9.1 lb). An average body mass of 3.64 kg (8.0 lb) was given in one account. Elsewhere, an average of 3.8 kg (8.4 lb) has been claimed. Slightly smaller weights were found in a South African survey where 5 males averaged 2.65 kg (5.8 lb) and 8 females averaged 3.71 kg (8.2 lb). Overall, they are the 9th heaviest living eagle species. The wingspan typically ranges from 1.51 to 1.81 m (4 ft 11 in to 5 ft 11 in). The largest authenticated wingspan for a female was 1.9 m (6 ft 3 in), with a claim of wingspans of up to 2 m (6 ft 7 in) 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 (Aquila rapax) or a short-toed snake eagle (Circaetus gallicus), 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 (Aquila chrysaetos). The wing morphology of the species gives it maneuverability in its densely wooded environment. The wing chord measures 445–532 mm (17.5–20.9 in), with a median of 467 mm (18.4 in) in males and 512 mm (20.2 in) in females. In South Africa, 5 males averaged 475.2 mm (18.71 in) in wing chord length and 7 females averaged 506.9 mm (19.96 in). 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 300 to 410 mm (12 to 16 in) long, with a median of 315 mm (12.4 in) in males and 348 mm (13.7 in) in females. South African males averaged 320.4 mm (12.61 in) in tail length in a sample of 4 and females averaged 352.4 mm (13.87 in). The bill is of a medium size relative to its body size, with one large museum specimen's bill measuring 55 mm (2.2 in) in length from the gape, 45 mm (1.8 in) in culmen length and 33 mm (1.3 in) in bill depth. In South Africa, culmen length averaged 50 mm (2.0 in) in 4 males and 54.9 mm (2.16 in) in 7 females, with a range in both 46.5 to 61.4 mm (1.83 to 2.42 in).<p>The tarsus is of a modest length for a raptor of its size, at 8.5–10.3 cm (3.3–4.1 in), 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 (or hind claw, which is the largest talon on accipitrids) of 6.2 cm (2.4 in), while another female was measured at 5 years of age, the age of sexual maturity, 5.74 cm (2.26 in) in the hallux-claw and an adult male measured 4.9 cm (1.9 in). In South Africa, hallux-claw length averaged 52.4 mm (2.06 in) in 5 males and 60 mm (2.4 in) in 7 females with a range in both of 48.6 to 61.4 mm (1.91 to 2.42 in). 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 10 cm (3.9 in), although, much like a single report of captive harpy eagles with a 13 cm (5.1 in) 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 4.74 cm (1.87 in), was around one cm less than that of a harpy eagle or the huge, recently extinct Haast's eagle (Hieraaetus moorei) and slightly smaller than those of the Philippine eagle (Pithecophaga jefferyi). 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.<p>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 genders' sexual 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 (4 or 5 per second) from the more sluggish female (3 or 4 per second).<p>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.

Taxonomie

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 (Aquilinae). 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.<p>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 (Nisaetus nipalensis) and the black-and-chestnut eagle (Spizaetus isidori), 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 (S. mahery) 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 (called by him the "bush eagles"), 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.

Wissenschaftlicher Name

Stephanoaetus coronatus

Autorität

(Linnaeus, 1766)

Ordnung

Accipitriformes

Familie

Accipitridae

Gattung

Stephanusadler

Verbreitung und Lebensraum

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 (once) 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.<p>The crowned eagle inhabits mainly dense woodlands, including those deep within rainforest, but will sometimes also be found in relict patches, wooded escarpments, riparian strips of Acacia, heavily wooded hillsides, and rocky outcrops throughout its range. The crowned eagle may be found from an altitude of sea-level to at least 3,000 m (9,800 ft). Owing to lack of current suitable habitat, the eagle's range is often somewhat discontinuous. In the Democratic Republic of the Congo, the crowned eagle has been confirmed to survive at relatively high densities in protected areas that maintain dense, old-growth rainforests. In Kenya, 84% of the crowned eagles range is within rainforest with an annual rainfall amount of more than 150 cm (59 in). Around stretches of East Africa where protected areas mostly consist of fairly open habitat, crowned eagles usually live in wooded areas of rocky hills and narrow riverine strips, only rarely ranging into savanna surrounding the hills. Southern Africa has been subject to the most comprehensive study of crowned eagle habitat, largely since many areas there would seem inhospitable to a large raptor often associated with old-growth forest. In southern Africa, its distribution south of the Limpopo River coincides largely with montane forest, although it is not restricted to that habitat and may range secondarily into plantations, usually of eucalyptus. In South Africa, it occurs in both lowland and montane evergreen forest, dense woodland, and forested ravines and gorges in open savannas and thornveld. In Zimbabwe, the crowned eagle can be found in quite open woods with Adansonia trees and may occasionally forage in savanna and secondary growth. In Malawi, highland birds forage in lower miombo woodland, and lower altitudes, breeding occurs in deciduous forest, more locally in dense miombo, tall riparian woodlands, and in remnants close to cultivation. Crowned eagles in Zambezi, occurs in evergreen forest in the eastern highlands, in rugged, hilly terrain over the central plateau, in hills and escarpments in the southeastern portions of the central watershed, and in riparian habitat along the larger rivers.

Zugverhalten

Resident species

Verhalten

Typical of most raptors that breed in Africa, the crowned eagle is non-migratory and is largely sedentary. This species usually inhabits a fixed territory throughout the year during its adult life. There is evidence that the birds move about to some degree when circumstances require it, for example when they need to change mates in isolated breeding areas. The greatest movement of any notable distance is usually associated with juvenile birds, which wander relatively widely before maturation. Forty-four birds of various ages that were ringed in southern Africa and recovered were all found near the ringing localities. Small movements by crowned eagles has resulted in them being sighted in improbable habitats, such as on an open savanna hill in Kenya, an open river bed in Lewa Wildlife Conservancy and even a golf course in Nairobi.<p>The crowned eagle is highly vocal and has a noisy, undulating display flight. In Equatorial Africa, they often call year-around, while elsewhere they may vocalize mainly in the context of breeding and nesting activities. The call is a series of loud whistles that rise and fall in pitch. The male performs an elaborate rise-and-fall display over the forest canopy both during the breeding season and outside it as a territorial proposition. Usually, territorial displays, which outnumber breeding displays, occur around the periphery of the bird's home range while breeding displays are likely to be over or at least near the nest. Displays consists of a series of steep dives and ascents, with a few wing-flaps at the top of each climb and descending circles and figures of eight. During descents, eagles can drop as much as 60 m (200 ft) at a time before circling back up. During this display, the male is noisy, uttering a shrill kewee-kewee-kewee while throwing his head back, often calling for a spell of approximately 30 seconds. The displaying male may reach heights exceeding 900 m (3,000 ft), sometimes even near cloud level at over 2,000 m (6,600 ft) above the ground. The adult female may also perform independent display flights, uttering a lower kooee-kooee-kooee. The female seems to display less often and tends to have a mellower voice. Pairs also perform visually striking mutual displays, sometimes arising from the first type or when the pairs come together after a brief absence. Spectacular tandems, interlocking talons and falling some distance from the sky are typical of mutual displays. Despite the spectacular and conspicuous nature of their display flights, the crowned eagle is sometimes considered a "clumsy" flier out in the open, lacking the grace and speed attributed to other eagles in a high-flying context, such as large Aquila species. While awaiting food at the nest, both the female and the young call out a penetrating, high kwee-kwee-kwee, that can border on incessant.<p>In disposition, the crowned eagle is considered nervous, constantly alert and on edge. They are quite different from the oft-stately open country eagles such as the Aquila species. In their training and management, crowned eagles are perhaps more reminiscent of a Goshawk (Accipiter gentilis) than Aquila eagles. Some linkage has been made between forest-dwelling habits and having a curious and edgy disposition amongst various raptorial birds. Ironically considering their otherwise hyperactive behavior, the main hunting techniques of crowned eagle require long periods of inactivity, spent sitting on a perch. Mature crowned eagles are reportedly nearly fearless towards humans and, unless shy from prior interactions, unusually prone to treat humans aggressively. Crowned eagles can nest around developed areas, including in the vicinity of quite suburban, developed areas (such as in view of apartment or office buildings), so long as prey is abundant and accessible and the habitat provides enough mature vegetation to facilitate nest building and hunting activities. Some biologists consider this species highly intelligent, cautious, independent and inquisitive when compared to other accipitrids. In falconry, crowned eagles cannot be induced to direct their hunting instinct towards large prey by increasing their hunger, as is done with Aquila eagles, for example. In the context of human interaction, wild, adult crowned eagles are quite the opposite of the martial eagle, which are typically very wary and tends to shun any variety of human activity. However, young crowned eagles in their post-fledging stage differ greatly in behavior from independent or adult eagles. Amongst post-fledging eagles in a semi-captive state, it has been noted that they border on helpless in terms of feeding and defending themselves compared to other accipitrids and are even described as "cowardly", unwilling to even simulate attacking prey until many months after fledging. This implies a learning element occurs in wild crowned eagles during their exceptionally long post-fledging period. Crowned eagles are reportedly variable in temperament as individuals to a degree greater than that found in most other raptors.<p>Crowned eagles have one of the most prolonged breeding cycles of any bird. It is common for raptors that live around the tropics to have a relatively elongated breeding period. Crowned eagle pairs breed once every two years; a single breeding cycle is approximately 500 days in duration. Most other eagle species complete a breeding cycle in under six months, or in about 35% of the time it takes the crowned eagle. While the incubation and nestling stages are about average for a tropical eagle (for example the black-breasted snake-eagle (Circaetus pectoralis), about half the weight of this species, has an incubation/nestling cycle of a similar length), it is the extraordinary post-fledging period of 9–11 months that makes the crowned eagles' breeding cycle so long. In harpy and Philippine eagle, although these are less extensively studied, it may take a similar or even longer amount of time for the young to attain full independence. A case of crowned eagle pairs that reportedly bred every year in South Africa are unsubstantiated but may be due to an apparently high population loss rate among juvenile eagles near areas that are heavily populated by humans. Breeding can occur almost year-around throughout the range, though egg laying seems to peak roughly around the end of the African wet season or the early dry season, from July to November. Territories or home ranges are maintained vigorously. In Zimbabwe, individual home ranges can vary from 140 to 200 km2 (54 to 77 sq mi) in size. Near the city of Nelspruit in South Africa, home ranges averaged 30 km2 (12 sq mi) in size. In southern Africa, the mean distance between active nest sites can range from 2 to 19.5 km (1.2 to 12.1 mi).<p>After engaging in the breeding display described above, the pair collaborate in building a massive nest in a fork of a large forest tree, typically from 12 to 45 m (39 to 148 ft) above the ground. While the female fetches more nesting material, the male tends to be more active in nest construction. In East Africa, many nests appear to be close to a forest river. Generally, crowned eagles seem to be attracted to the taller trees in the forest. On the Nyika Plateau in Malawi, the favorite nesting trees are the large emergent Aningeria adolfi-friederici and Gambeya gorungosana, and a pair in the Lower Shire used a Sterculia appendiculata tree. In Zimbabwe, Newtonia buchananii are reportedly one of the most used tree species for nesting. Exceptional crowned eagle nests have been observed on sheer cliff faces. In southern Africa, the species nest in drier and denuded terrain than expected such as Adansonia stands on semi-arid hillsides. Despite the relative sparseness of this habitat, these sites have a varied and convoluted terrain, with nooks and crannies, valleys, overhangs and hideaways that allow a crowned eagle to exercise its particular hunting skills. In Kenya, similar fractured landscapes can also be utilized by crowned eagles, such as the black gigantic volcanic rubble fields of Tsavo West National Park, the lower Chyulu Hills, Kibwezi and Soysambu Conservancy. These are jungles of boulders covered with low growth interspersed (in the past) with high trees. A nest built from scratch may take up to 5 months to construct, however existing nests are often repaired and re-used during successive breeding seasons, a process that can take as much as 3 months. It is typical for an eagle pair to use a nest for more than five years and, unlike several other booted eagles, crowned eagle pairs rarely build more than one nest for alternative use. Most large eagles build a very large nest and the crowned eagle is no exception, as it builds one of the largest nests of any eagle. In the first year they build a nest, it may measure 1.5 m (4.9 ft) across and 50 cm (20 in) deep. However, a larger nest, usually after several years of usage, may measure up to 2.5 m (8.2 ft) across and up to 3 m (9.8 ft) deep. The nest consists of both dead and greener branches and has a light coverage of leaves and animal matter. Copulation takes place in the nest, several times a day. Reportedly copulation can occur up to a year before laying, although these may be exceptional cases of mating for non-fertilization purposes (which, in other eagles, has been thought to be related mainly to strengthening pair bonds). A pre-copulation display typically occurs, wherein the male runs repeatedly around the crouching female with wings upraised, which displays the chestnut of the under-wing coverts and beautiful barring.<p>In South Africa the crowned eagle lays its eggs from September to October; in Zimbabwe, it lays from May to October; mainly nearer to October around the Congo River; anywhere from June to November in Kenya, with a peak in August through October; in Uganda from December to July; and in West Africa, laying peaks in October. The clutch of the crowned eagle either contains 1 or 2 eggs. Often in East Africa, just one egg is laid. Eggs are usually just white, though may sometimes be overlaid with sparse red-brown markings. The eggs are moderate in size, averaging 68.2 mm × 53.6 mm (2.69 in × 2.11 in), with ranges of 60.9–75.5 mm (2.40–2.97 in) in length and 50.8–57.9 mm (2.00–2.28 in) in width. When a natural disaster befalls a nest, a replacement may be made in 2 months time. Incubation lasts for approximately 49 days. 80–90% of egg incubation is done by the female during the day. Food is mainly brought to the nest by the male in the early stages of breeding, though sometimes both sexes may deliver food. The male brings food to the incubating female every 3 to 5 days. When they initially hatch, the young tend to be quite quiet. If two eggs are laid, the younger one dies by starvation after being outcompeted for food by the older one or even directly killed by its older sibling. No nest of wild crowned eagles has been known to successfully produce more than one fledgling, though in captivity two have been known to survive with human assistance (supplementally feeding the younger chick or taking it out of the nest). In cases where the older nestling dies, the younger one may be fed more regularly and survive.<p>After hatching, the male kill rate rises to one kill every 1.5 days. Pair behavior while raising chicks is very variable, some males are very attentive to their young, while others leave virtually all brooding to the female. After 40 days of age, the young is capable of feeding itself, though is often still fed. The first feathers through the white down emerge when the crowned eagle chick is 40 days old, with the feathers ultimately covering the down in 76 days. After 76 days, the main feather development is in the tail or the wings. Wing flapping begins at 45 to 50 days, increasing after around 75 days. The young fledge at 90 to 115 days, with an average 110.6 days and any period of time less than 100 days is considered unusually soon. On average, male chicks tend to be more active wing-flappers and usually will first fly around 10 days earlier than female chicks. After fledging, females are attentive 95% of the day and brood 50–75% of the day, the amount decreasing slightly with each day. The female does much of the prey capture and a majority of the nest defense after the young fledge. After fledging, the young remain in the neighborhood of the parent's nest and are fed every 3 to 5 days by either parent for their first 270–350 days of life. The rate of food-delivery varies from several times a day to every 3 days on average during the post-fledging period. The fledged juvenile will solicit adults (apparently even unrelated adults) for food but does not actually take the prey unless this occurs around the nest site. The first recorded kill for a young crowned occurred 61 days after fledging, although this is considered exceptionally early by the standards of this species. Flights increase incrementally through the post-fledging period, although the young do not engage in rising flights until they are fully independent. Independence appears to be triggered by the increased indifference of parents to bringing food. Due to the loud vocal interplay between the parents and the fledging eagle, the adults seem to take it as a sign that their offspring has sought independence if they return to the nesting area and hear no begging auditory response. The young eagle usually remains in the care of its parents for a total of up to 11 months after it fledges, longer than is known in almost any other raptor. The advantage of this prolonged stretch to independence is that it may make for a stronger young eagle when compared to other accipitrids which have almost no post-fledging dependency period. In 34 possible cases, 18 resulted in eggs being laid. Fledging success is approximately 83% and almost all young that leave the nest also reach independence. It is estimated that most crowned eagles will reach breeding maturity at around five years old, as is typical for other large eagle species.

Schutzstatus

Bestandstrend

declining