Águila Imperial Oriental

Identificación

The eastern imperial eagle is a large eagle, but usually falls near the average size of the large-bodied genus Aquila. Adult total length can range from 68 to 90 cm (27 to 35 in) with a typical wingspan of 1.76 to 2.2 m (5 ft 9 in to 7 ft 3 in). The average wingspan of a small sample showed males to average 1.95 m (6 ft 5 in) while a small sample of females averaged 2.07 m (6 ft 9 in). Although otherwise outwardly similar, the species displays reverse sexual dimorphism as do most birds of prey, in which males are usually smaller than the females. For the eastern imperial eagle, females are up to 10% larger linearly and 40% heavier in body mass in some cases. In terms of body mass, one survey found five males to weigh from 2.45 to 2.72 kg (5.4 to 6.0 lb) and five females to weigh from 3.26 to 4.54 kg (7.2 to 10.0 lb). The average weight of this sample of imperial eagles was reportedly 2.62 kg (5.8 lb) in the males and 3.9 kg (8.6 lb) in the females. A sample of unknown size showed males to weigh an average 2.88 kg (6.3 lb) while females reportedly weighed an average of 3.38 kg (7.5 lb). A further two mature females weighed an average of 3.56 kg (7.8 lb). Among standard measurements, males may range in wing chord length from 540 to 622 mm (21.3 to 24.5 in), in tail length from 260 to 308 mm (10.2 to 12.1 in) and in tarsus length from 91 to 98 mm (3.6 to 3.9 in). Meanwhile, females may range in wing chord length from 565 to 665 mm (22.2 to 26.2 in), in tail length from 270 to 330 mm (11 to 13 in) and in tarsus length from 97 to 107 mm (3.8 to 4.2 in). A sample of imperial eagles ranged in total bill length from 65.7 to 76.5 mm (2.59 to 3.01 in).<p>In general, compared to other species in their taxonomic group, the eastern imperial eagle has a relatively long and thick neck, a big head and bill (with a gape line level with middle of eye), a longish square tipped tail, somewhat long and well-feathered legs and strong feet. The species tends to perch in a fairly upright position often on rather exposed tree branch or low mound, rock, haystack or similar convenient site. For an Aquila eagle, it is seemingly relatively less shy and bolder in the presence of humans. The adult plumage is largely a tar-like blackish-brown but for a well-demarcated and highly contrasting creamy to golden buff colour about the crown, hindneck and neck sides. Furthermore, adults have bold white ”epaulettes” on their shoulder braces, which are usually fairly conspicuous on perched birds. The adult's tail is narrowly dark barred over a greyish ground colour and has a broad black subterminal band, while a white tail tip sometimes manifest in adults that are freshly molted. The undertail coverts are sometimes indistinctly paler, rust to creamy, combined with grey tail base to give the appearance of a paler rear end. At rest, the wing tips tend to reach the tail tip. The juvenile eastern imperial eagle is mostly pale tawny-buff to sandy yellow with fairly heavy dark brown streaks from the throat down to the breast, mantle, scapulars and forewing coverts. The juvenile's scapulars and forewing coverts also have sometimes noticeable white tipped feathers while the median coverts are perceptibly browner and greater coverts blackish both with broad creamy-yellow tips forming clear wing bars. The flight feathers and tail on juveniles are often blackish and tipped whitish, however the white parts on the lower back to tail coverts are only lightly streaked in the centre and often not visible when perched. Below the streaked breast, the remainder of the juvenile's underparts are plain pale buff. By the 2nd year, the brown streaking on the underside fades to a plainer sandy hue and the pale bars also start to fade on wings. Especially later into the 2nd year into the 3rd year, some young eastern imperial-eagles show an erratic blotching of blackish-brown feathers below. By about the 4th winter, as the birds enter their subadult plumage, the forefront of the eagle is often a rather patchy mix of sandy and darker adult-like feathers. During slow annual molts, the dark feathers expand initially from the throat and upper breast outward. Late into the subadult stage, the birds also start to develop a pale crown and nape but usually the rear body still more juvenile-like, such as the pale rump-band and crissum despite the otherwise darkening tail and wing feathers. The full adult plumage is attained at 5–6 years of age but some subadults are already breeding before this.<p>In flight, the eastern imperial eagle is a large raptor that has for an Aquila a very projecting neck and "huge" head and bill. The long wings may appear fairly broad when compared to other, smaller raptors, but are relatively narrow with even parallel edges when compared to other Aquila eagles. Their flight style is relatively heavy but steady with deep powerful beats but they are not uncommonly clumsy at first takeoff. They tend to soar with forward pressed but rather flat wings, the outer wing feathers may sometimes curve up but as a rule they do not fly with a V as do some other Aquila. The species may also hold their wings flat while engaging in a glide but as it accelerates they may arch wings back. In flight, the adult from above shows dark brown with small white braces, greyish tail with fine dark bars and a very broad, blackish subterminal band. The adult is essentially all dark colored when seen from below relieved only by some very dusky grey flight feathers on the primaries (against the black wing tips), a grey crissum and thinly barred grey tail base. However, these features may be only obvious in good light and at reasonable distances. In flight, the juvenile is largely pale buff with brown streaking. The lower back, rump, tail coverts and leg feathers are all whitish cream in colour which contrasts noticeably with their white-tipped blackish greater coverts, primary coverts and quills. On their mantle, juveniles manifest two white wing bars above and a narrow whitish lower trailing edge. Meanwhile, the juvenile's inner primaries are much paler creamy-buff hue than their other flight feathers. The dusky brown wing linings of the juvenile plumage, when compared to the darker ones of adults, show more extensive coarse patterning. Some birds by 2nd to 3rd year are so worn in their flight feathers as to appear almost unstreaked sandy while, from the 3rd year on, darker feathers start to appear below with various untidy variations.<p>The eastern imperial eagle is typically smaller, being more slender and less bulky and powerful in appearance despite its proportionately larger head and longer neck, than the golden eagle (Aquila chrysaetos). In some parts of the range, the female imperial eagle probably averages similar size and body mass to the smaller male golden eagle. However, apparently the species can be reliably distinguished by the size of its hallux claw (the enlarged rear talon that accipitrids used as a killing apparatus) which is consistently larger in the golden species. Two female eastern imperial eagles measured 38 and 43 mm (1.5 and 1.7 in) in hallux claw length while a male was about 35.5 mm (1.40 in), whereas the smallest talon measured for an immature male American golden eagle was 44.9 mm (1.77 in). Nonetheless, besides its wider ranging golden cousin, this species is typically the largest, with the largest extremities (i.e. tarsal, tail and bill length) and most powerful booted eagle species in the majority of its range (apart from its rare African winter range) when compared to similar eagles such as others in the genera Aquila and Clanga. In their winter quarters in South Asia, this species rivals a fish eagle as the largest and most dominant eagle species. Usually, the plumage of the adult eastern imperial eagle is very distinctive. It is considerably darker than other adult Aquila eagles in central Eurasia. Furthermore, all other Eurasian eagles in their range lack the white spots on the wing mantle and greyish under-tail. Given reasonable views, the juvenile imperial eagle is no less distinctive, with its unique tawny-buff covered in brownish streaking, a colour combination not seen in other species. From a distance, the juvenile may give the impression of a dark mantle and chest band with very pale rear body and a blackish tail and remiges against strikingly pale primary wedges. Adults do however strongly resemble their considerably extralimital cousins, the Spanish imperial eagle, but the eastern species has more restricted white on the shoulder and has a slightly more brownish hue in the dark underside feathers, while juvenile Spanish imperials are richly tawny in colour rather than pale buffy and lack brownish streaking on the body. The Spanish species is similar in size and proportions to the eastern imperial but is marginally heavier on average and has an even more protruding head and neck.<p>The subadult eastern imperial eagle may be confused with older immature greater spotted eagles (Clanga clanga) but the latter is less contrastingly patterned, without a paler shawl and has greater covert band below (despite the rare hint of one on some imperials) and densely bared flight feathers. Adult greater spotted eagles have similar underwing contrast as juvenile eastern imperial eagles but, beyond plumage characteristics, are distinct for their much smaller head, slightly smaller overall size and more compact frame with a relatively broader and shorter wings. More similar to the juvenile eastern imperial eagle is the fulvescens morph of the greater spotted eagle which is fairly rare (more so in the west) but is similarly or even as pale buffy. However this spotted eagle morph lacks the brownish streaks below of the juvenile imperial and further has contrasting much darker feathering on the wing coverts (heavily spotted in juvenile greater spotteds) and mantle as well as sometimes the facial feathers, and can further be distinguished by the same aforementioned differences in form. Indian spotted eagles (Clanga hastata) tend to show paler lesser under-wing coverts like juvenile eastern imperial eagles but are considerably smaller and differ in all other proportions and plumage features. Although at times described as “very similar”, the eastern imperial eagles are fairly easily told from the golden eagle by being much darker with less broad wings that are held much flatter. The golden eagle, unlike imperial eagles, tends to fly with its wings pointed upwards and have a gradual tapering wing shape (somewhat narrower at the base, broader at the primaries). In golden eagles, the tail generally appears narrower and squarer in shape. At closer range, the pale area on the back of the head and neck in eastern imperial eagle may be suggestive to some of the golden eagle's golden nape but is always much paler and chalkier in colour, as well as more strongly contrasted by the otherwise dark feathers and is more extensive. Against the somewhat similarly sized but more compact juvenile steppe eagle (Aquila nipalensis), the juvenile eastern imperial eagle does not show a white band on underwing like the steppe. More obviously, the steppe eagle lacks the paler overall colours and contrasting brownish streaking of juvenile imperials. Feather wear can make the wing shape of the two resemble the other but the larger head and less compact frame of the imperial species render its flight profile distinctive. The only darker large booted eagle encountered by the eastern imperial eagle, in its African winter quarters, is the jet-black Verreaux's eagle (Aquila verreauxii) which is more suggestive in size and proportions of the golden eagle. An unlikely source of confusion, the Verreaux's differs in almost all plumage characteristics and has far more tapered wings that pinch in at the base and, like the golden eagle, tends to fly in a fairly strong dihedral. In Asia, its proportions and size may be suggestive of the perhaps even rarer Pallas's fish eagle (Haliaeetus leucoryphus) and the two can potentially be mistaken in strongly backlit conditions which obscure their obviously distinct plumages. The large headed and flat winged shape of the imperial eagle may too suggest in silhouette the white-tailed eagle (Haliaeetus albicilla) but that species is usually rather larger bodied and even larger headed with much broader wings and a proportionately shorter tail. Cinereous vulture (Aegypius monachus), being similarly dusky overall below, have been suggested as confusion species, but are much larger than imperial eagles with differing proportions (far broader wings, proportionately smaller head and shorter tail) and lack any of the contrasting pale parts of the imperial eagle's plumage.<p>The eastern imperial eagle is quite vocal on their breeding ground but tends to be silent or nearly so elsewhere. The main call of the species is a deep, harsh bark owk owk, gok gok or kraw-kraw. The call tends to be repeated rapidly up to 8-10 times. Their call is perceptibly deeper and harsher than that of the golden eagle, somewhat incongruously also being more resonant and commanding. Sometimes when extending to a prolonged version, its call is sometimes considered reminiscent of the croak of a large frog. The eastern imperial eagle most frequently calls during their aerial displays. In extreme cases, the call may be repeated up to 13 times during an aerial display. Furthermore, they may repeat the call from a perch. Females may also call when a male arrives with prey. Alarm calls recorded for the species include a soft ko-gok, wk wk wk, uttered in response to a distant intruder, a closer approach also may cause a harder gek call by the mother. A rising and falling trill has been additionally recorded in captivity is also probably an alarm call.

Taxonomía

The eastern imperial eagle is a member of the Aquilinae or booted eagles, a rather monophyletic subfamily of the accipitrid family. At least 38 species are currently housed in the subfamily, all with signature well-feathered tarsi. This species is a member of the genus Aquila, which are mostly large, fairly dark colored eagles distributed largely through the more open habitats of Eurasia and Africa (with one in North America and a couple in Australasia). Studies on DNA have indicated that the imperial eagle is part of a subgroup with other moderately sized Aquila such as the steppe eagle (Aquila nipalensis) and the tawny eagle (Aquila rapax). Despite the outward resemblance to the imperial eagle, the 4 species in the golden eagle subgroup appear to be rather more closely related to the dissimilarly smallish and pale-bellied sister species, African hawk eagle (Aquila spilogaster) and Bonelli's eagle (Aquila fasicata). The Spanish imperial eagle, which is found in Spain and Portugal, was formerly lumped with this species, the name imperial eagle having been previously used in both circumstances. However, the two are now regarded as separate species due to significant differences in morphology, ecology and molecular characteristics. It is likely that the eastern imperial eagle is the paraspecies for the Spanish imperial eagle and that the imperial eagle complex reached the Iberian peninsula sometimes between the late Pleistocene era and early Holocene. The Spanish imperial eagle may be considered an ice age relict due to its isolation.

Nombre científico

Aquila heliaca

Autoridad

Savigny, 1809

Orden

Accipitriformes

Familia

Accipitridae

Género

Aquila

Distribución y hábitat

The eastern imperial eagle is found as far west as east-central and southeastern Europe. The European part of its breeding range includes eastern Austria, eastern Czech Republic, Slovakia, Hungary, eastern Croatia, Serbia, northeastern Bosnia and Herzegovina, Macedonia, Bulgaria, Romania, Moldova and northern, western and much of the eastern part of the Ukraine. The species distribution continues across central Russia, where it is found through most of the Central Federal District, essentially all of the North Caucasian Federal District, most of the Volga and Ural Federal Districts (excluding the northern parts), and the southern part of Siberia past Lake Baikal to the Transbaikalia in the landlocked southwest of the Russian Far East. Out of Russia, their breeding extends south to mostly the northern portions of the following nations: Georgia, Armenia, Azerbaijan, Turkmenistan, Uzbekistan, much of Kazakhstan, northwestern China (Xinjiang) and northern Mongolia. Isolated populations also persist in northwestern, central and eastern Turkey, Cyprus, and northern Iran. As a breeding species, they are probably extirpated from Afghanistan and Pakistan.<p>Unlike the Spanish imperial eagle, the eastern imperial eagle is fairly strongly migratory in most of its range, though a variable amount of residency or very local wandering during winter in the western and southern parts of its range may lend it to be described as a partial migrant. The species has been recorded overwintering as far north as Mongolia. In Bulgaria, of three post dispersal juveniles, two wandering within the country and only one migrated a long distance to Israel. Migratory movements occur during fall any time from September to November and in spring anytime from February to May, shifting earlier in the fall and later in spring the farther north that the eagles breed. Differentiating the large areas use merely for passage migration or vagrancy from regular wintering grounds can be difficult. Though typically seen in very small numbers at main raptor migration sites the species may occur as a passage migrant through much of the Middle East down to Yemen, with pockets of wintering eagles in Israel, northern Jordan, central Saudi Arabia, Kuwait, northeastern Iraq and adjacent southwestern Iran. A radio-tagging study of a few wintering eagles in Arabia found they returned variously to Russia in four cases and Kazakhstan and China in a single case, with a range of ground covered in spring migration of 3,900 to 5,000 km (2,400 to 3,100 mi). The eastern imperial eagle winters locally and in quite small numbers in Africa's Nile valley, mostly being reported in southern Sudan, central Ethiopia and northern Kenya, irregularly down as far as southern Kenya and once even northern Tanzania. Most migrants to Africa apparently originate in the western part of the breeding range such as Europe. Further east, such as the imperial eagles that breed around Lake Baikal, will generally migrate to south Asia. Moderate to quite low numbers are usually noted of this species at migration sites in the Himalayas. The eastern imperial eagle winters fairly broadly in the Indian subcontinent, from eastern Pakistan, eastward through southern Nepal to Bangladesh and down as far south in India as the states of Gujarat, Madhya Pradesh, Bihar and northwestern Jharkhand. Other semi-regular wintering areas include southern Bhutan, Thailand and north Indochina (recorded across Chinese border in southwestern Yunnan) and spottily in east China where wildlands still occur. Occasionally, wintering birds are known to occur in the central Cambodia and discontinuously in Laos and Vietnam as well as in the Korean peninsula, Taiwan and southern Japan (mostly Honshu). Vagrants have been reported in over 20 countries, mainly in Europe, including Poland, Sweden, Denmark, Germany and Italy.<p>The eastern imperial eagle is distributed as a breeding species largely along the southern edge of the vast taiga forests. The habitat preferred by the species is often rather open country with scattered trees or more enclosed woodlands, as well as around or near wetlands. The imperial eagle often forages mainly in open areas, extending to beyond typical assorted grasslands to wetlands and agricultural areas. In more extensive wooded areas, eastern imperial eagles require glades or meadows in order to executive hunting. The central part of their range as a breeding species occurs in vast areas of steppe and here the species often inhabits forest-steppe mosaics, as well as open woodlands, river valleys and even agricultural areas with trees or wooded patches. Lowland areas tend to be preferred, albeit not exclusively. In Turkestan and Kazakhstan, they may extend their breeding habitat into semi-desert. True desert is used during winter so long as foods are available. Largely where golden eagles are absent, the species has been reported to range into secondary habitats such as forested lower mountains and montane steppe and meadowland. In Europe at least, this is due to human pressures, which caused them to abandon open lowlands, timbered plains and river-fringed forests for forested, precipitous uplands. A slow repopulation of their preferred lowlands reported since the 1990s in Slovakia and Hungary. Often, eastern imperial eagles winter in more open habitats such as nearly continuous grassland, plains, semi-desert and cultivation with scattered trees as well as various marshes, lakes and other wetlands. The species resides mainly from sea level to 1,300 m (4,300 ft), locally to 1,800 m (5,900 ft), and has been recorded on passage at 3,900 m (12,800 ft) in Asia.

Área de cría

PAL : se Europe to c Siberia

Área no reproductiva

OR, Arabian Pen. and ne AF

Migración

Migrantes completos

Comportamiento

Patrón migratorio: Migrantes completos.

Conservación

Tendencia poblacional: en declive.

Tendencia poblacional

en declive