Aquila rapace

Identificazione

The tawny eagle is considered to appear "inelegant, scruffy-looking" but has a fairly characteristic aquiline silhouette. The species has a fairly long neck and long deep bill with a gape line level with the eye, moderately long wings with fairly pronounced "fingers" and a slightly rounded to almost square-ended and shortish tail, which can be more reminiscent of the tail of a vulture than that of other eagles. The feathering on the legs is extensive and can appear almost baggy-looking. The bill and head are strong and bold, the body well-proportioned and feet are powerful while the countenance is quite fierce-looking. While perching, the tawny eagle tends to sit rather upright, often on stumps, posts, low trees or treetops for long periods of the day or may descend to the ground to walk somewhat unsteadily with a more horizontal posture. The wingtips when perched are roughly even with the tip of the tail. Adults have variably colored eyes, ranging from yellow to pale brown to yellow brown, while those of juveniles are dark brown. Both the cere and feet are yellow at all ages. The tawny eagle is polymorphic with considerable individual variation in plumage, resulting in occasional disparities in plumages that can engender confusion in some. In adulthood, they can vary in coloration from all dark grey-brown to an occasionally streaky (or more plain) foxy-rufous to buffish-yellow. Most adults are usually a general grey-brown or rufous-tawny color, with occasional pale spotting visible at close quarters on the nape and belly, coverts uniformly toned as the body. The nape is consistently dark and uniform despite the feathers often being tipped paler with other feathers in adults, lacking the contrasting paler feathers often seen in other Aquila. Females, in addition to being slightly larger, may tend to be slightly darker and more streaked than the males. The most blackish-brown individuals tend to occur in India. Adults often show relatively little varying colors apart from their somewhat blacker wing and tail feathers, though when freshly molted great wing coverts and secondaries may show small pale tips which may form pale lines along closed wing has tawny upper parts and blackish flight feathers and tail. The head is often similarly tawny in colour as the body but may also sometimes shows darker eyebrows, other thin brown streaks or a darker chin. Meanwhile, the tail is plain or obscurely dark barred (with around 7 subtle bands). The dark morph adult is essentially all dark, dull brown. Some dark morph tawny eagles with wear may show irregular streaking or molting browns and more blackish feathers. Intermediate morph are dark to rufous brown above with the mantle and wing coverts variably streaked or molted lighter rufous as is the head with the crown or crown-sides being paler. The intermediate morph's underside is largely rufous (especially farther south in Africa) with breast and flanks very heavily and broadly streaked dark brown, though at times appears all dark brown contrasting with plain trousers and crissum. Pale morph adult tawny eagles always show a clear contrast between the pale body and wing coverts which bear darker flight feathers and tail. In pale morphs, the underparts are rufous buff to lighty tawny-brown, phasing into somewhat darker lesser and median wing coverts to darker brown to even blackish greater coverts and flight feathers. The head may too be tawny in pale morph tawny eagles but sometimes with thin brown streaks or darker chin. Below pale morph adults are all light rufous to tawny buff or brown, sometimes paler below the belly area. In worn individuals the bodily feathers of pale morph tawny eagles can appear almost whitish. Dark morph juvenile tawny eagles are generally light rufous to rufous brown with creamier lower back to upper tail coverts. Juveniles show thinly pale-tipped dark brown greater coverts and remiges while the tail is barred grey and brown usually with a narrow creamy tip. Dark morph juveniles may fade to pale buff or creamy often before molting into browner plumage. Subsequent stages are not as well-known but it appears dark morph subadults gradually manifest a darker brown or rufous brown color on the mantle, as well as on the head and upper breast while maintaining a buffish rear body (i.e. lower back and rump patch). Generally other morphs are similar but not as well-known and are perhaps individually inconsistent. Many are rufous or sandy after a molt but have mottling later on, the extent of pale feathers indicative perhaps of their ultimate adult morph.<p>In flight, the tawny eagle appears as a large raptor with a noticeably protruding head on a long neck, with a deep chest, long and broad wings with a somewhat narrower seven-fingered hand. The trailing edge of the wing is slightly curved outwards, indenting at the junction of primaries and secondaries, whilst the rounded, medium-length tail is usually held spread. The deep beats of the kinked wings can make their flight appear rather heavy and slow but they are quicker and more expansive in wing movements and often less forceful-looking than larger Aquila like steppe eagles and can be very agile when chasing other raptors to rob them. Tawny eagles soar with flat wings or very slightly raised and hands only slightly lower, and may fly similarly in a glide but may too arch when in a fast glide. Adult dark morphs are more or less uniform dark brown above and below, showing indistinctly and slightly paler and greyish primaries on both sides. Above, the main contrast on dark morphs above is paler creamy rump patch while, on the underside, the greyish color is contrasted with blackish tips and a diffused trailing edge along both the wings and tail. Intermediate morph tawny eagles are variably rufous streaked on brown to rufous brown on the back and wing coverts with a similar contrasting pale rump above as dark morphs. Below the intermediate's heavy dark streaks are only subtly different and their coloring can appear almost uniform. The wing quills of intermediate morphs are often greyer with a stronger contrast of the paler inner primaries and blackish wing ends. Pale morph are all pale tawny or buffish on both sides of the wing, which contrasting strongly with demarcated dark brown about the greater coverts, flight feathers and tail and usually the scapulars. The primaries are quite pale on pale morphs with sometimes the hint of a pale carpal comma. Some pale adults have pale bases to all the underprimaries and the quills are sometimes unbarred, but more usually the feathers have dense but narrow dark bars. Dark morph juveniles are light rufous to pale tawny body above which contrasts strongly with dark brown greater coverts, rear scapulars, flight feathers and tail, in turn all highlighting the creamy lower back to tail coverts. Below dark morph juveniles can look similar to pale morph adults apart from trailing whitish edges and often irregular pale diagonals along tips of greater wing coverts, though usually these fade early on. Little is known plumage development but the young eagles moult into brown, becoming patchy with intermediate often showing 1-3 darker bars on wing linings. The underparts of subadults (i.e. around 2 to 3 years or old) are typically two-toned, with darker brown about the breasts, belly and underwings coverts while the remainder of the underbody is creamy light in colour. This two-toned pattern is evinced in subadult tawny eagles both from India and Africa. Adult plumage is obtained between the 4th and 5th years of life.<p>This is a large bird of prey, though is medium-sized for an eagle and it is one of the smaller species in the genus Aquila. Among currently accepted species in the genus, it is of quite similar size to Bonelli's eagles (Aquila fasciata) (though is notably longer winged), slightly larger than African hawk-eagles (Aquila spilogaster) and much larger than Cassin's hawk-eagles (Aquila africanus). Otherwise, females of the larger species of Aquila are frequently around twice as heavy as an average tawny eagle. As is typical in birds of prey, the female tawny eagle is larger than the male, though relatively modestly so and a difference between the sexes is typically up to 15%. In total length, tawny eagles can measure from 58 to 75 cm (23 to 30 in). A typical length for a tawny eagle is considered about 65 cm (26 in). Wingspans can measure from 157 to 190 cm (5 ft 2 in to 6 ft 3 in). Weight can range in fully grown birds from 1.5 to 3.1 kg (3.3 to 6.8 lb). Average weights were reported in one study as 1.91 kg (4.2 lb) in 5 males and 1.97 kg (4.3 lb) in 5 females. In another study, 10 unsexed adult tawny eagles were found to have weighed 2.5 kg (5.5 lb) on average while, for the same data pool, a sample of 15 had an average wingspan of 182.9 cm (6 ft 0 in). Another small sample of African males, sample size four, averaged 1.85 kg (4.1 lb) while three females averaged 2.28 kg (5.0 lb). The mean mass of the species in one estimate was 2.3 kg (5.1 lb). In all standard measurements combined, the wing chord can vary from 473 to 565 mm (18.6 to 22.2 in), the tail from 242 to 295 mm (9.5 to 11.6 in) and the tarsus from 79 to 92 mm (3.1 to 3.6 in). The culmen length of Kenyan tawny eagles was measured at 33.3 to 42.4 mm (1.31 to 1.67 in), averaging 37.7 mm (1.48 in), while the gape width is 44 mm (1.7 in) on average, ranging from 40.3 to 49.9 mm (1.59 to 1.96 in). The hallux-claw, the enlarged rear talon often used as a killing instrument on accipitrids, can measure from 27 to 37.7 mm (1.06 to 1.48 in), averaging 31.8 mm (1.25 in) in one sample and 32.3 mm (1.27 in) in another. The talon size is not especially large for a booted eagle and is proportionately similar in size to those of steppe eagles and eastern imperial eagles (Aquila heliaca).<p>The tawny eagle lives in multiple areas where other broadly similar brownish hued and largish raptors often occur. Thus identification is seldom straightforward.<p>One source that can especially engender potential confusion in its wintering range is the formerly conspecific steppe eagle. The steppe is larger with a shorter neck, relatively longer and narrower wings, a more massive beak, particularly via the exceptional depth of the gape (although in flight can appear smaller headed due its less protruding neck) and has a longer and rounder tail. Furthermore, steppe eagles tends to have much bolder and widely spaced barring on the wings than tawny eagles and more distinct dark trailing wing edges and paler throats.<p>Beyond steppe eagles, comparisons to various other groups of sympatric booted eagles may be made. Compared to the spotted eagles, the tawny eagle's tail is longer, the bill more prominent, the wings usually less squared-off in flight, the neck longer and the overall look rangier, despite these species being of often similar size. In contrast to the imperial eagles, the wings of the tawny eagle are broader and have less even trailing edges, the bill is slightly less prominent, and the wings are more likely to be held slightly upwards, while the body size is smaller. When compared to the golden eagle species complex, of which only the golden and the Verreaux's eagle (Aquila verreauxii) are usually relevant (although three dissimilar and sympatric pale-bellied eagles, of a size with tawny eagles or smaller, are found as part of this evolutionary chain), the tawny eagle is considerably smaller, its wings do not taper as much nor are they as likely to be held in a strong dihedral, and proportionately, the bill is notably longer and the tail is rather shorter. Greater spotted eagles (Clanga clanga), like the steppe eagle a Palearctic breeding eagle who often winters in the resident range of tawny eagles, is fairly similar, but that species has a relatively shorter and broader tail, less baggy feathers on the legs and usually a rather darker and more uniform adult plumage. The fulvescens form of the greater spotted eagle must be distinguished from the pale forms of the tawny eagle by its underwing pattern, often with completely blackish underwing coverts and usually plain looking dark remiges over the entire primaries with more distinct pale carpal arcs. The likewise migratory lesser spotted eagle (Clanga pomarina) is smaller than the tawny eagle and more compact with a distinct white U above the tail. The residential African Wahlberg's eagle (Hieraeetus wahlbergi) can have a similar uniform plumage as in tawny eagles but always has greyer flight feathers and is much smaller than tawny eagles with relatively longer and more rectangular wings and a longer, narrower and straighter-tipped tail. The eastern imperial eagle in juvenile plumage can appear similar to the pale and intermediate morph tawny eagles, but the imperial eagle is usually visibly larger, with slenderer, longer wings, a longer, broader tail as well as having dark brown streaking on the chest, mantle and wing coverts and bearing more distinct pale trailing edges and wing bars.<p>Dark-morph tawny eagles in India may be distinguished from similarly sized black eagles (Ictinaetus malaiensis) by the latter being slenderer and having longer, darker and more paddle-shaped wings with a narrower base and a much longer, narrower and distinctly barred tail. More dissimilar eagles such as Circaetinae, i.e. brown snake eagles (Circaetus cinereus), black-breasted snake eagles (Circaetus pectoralis) and juvenile bateleurs (Terathopius ecaudatus), are sometimes mentioned as a potential source of confusion but are usually rather distinct (all larger headed, rather smaller billed, shorter tailed and bare legged with often less uniform coloring) even in their most similar hues.<p>Tawny eagles are generally silent in most of their range. However, unlike steppe eagles, which are almost always silent away from their breeding grounds, they are said to occasionally vocalize in any season. They are also more vocal when not breeding than the spotted eagles. The usual call is a harsh, hollow-sounding, loud bark, variously transcribed as kowk-kowk, kau-kau, kiok-kiok or ki-ark. The call is fairly high-pitched (slightly less deep than the steppe eagle's when the latter is breeding) but is still deeper voiced than spotted eagles. In Kruger National Park it is said the call is loud and far-travelling. Male tawny eagles are the most frequent vocalizers in the species, particularly during sky-dances, but also in other contexts. These include but are not limited to food arguments, disturbances during nesting and males attracting females for food passes. In nine years of monitoring tawny eagles in Zimbabwe, however, the call was not heard once. Its silence there may be due to the flat landscape. Other call recorded include a harsh grating k eke ke... in aerial courtship displays and a throaty kra in kleptoparastic pursuits. A kra-kra call may emitted at times to warn intruders. The female may also emit an occasional mewing, high shreep-shreep at the nest as well as a rare raucous scream (possible food-begging and alarm calls, respectively). The young chick tawny eagle chips initially but once its feathers emerge, it tends to beg with a loud call, i.e. we-yik, wee-yik.

Tassonomia

Dutch naturalist Coenraad Jacob Temminck described the tawny eagle in 1828 from an Indian type specimen. "Tawny eagle" has been designated the official name by the International Ornithologists' Union (IOC). Aquila is Latin for “eagle” while rapax is also Latin for “to grasp”, and relates to the word rapacious, i.e. highly predatory. The tawny eagle is a member of the booted eagle subfamily (Aquilinae) within the Accipitridae family. The booted eagle clan are monophyletic and study of karyotypes has indicated that they likely have few to no close external relations within the overall extant accipitrid family. The booted eagle subfamily all have feathers covering their legs and are distributed in every continent that contains accipitrids. The genus Aquila has been traditionally defined as largish, dark-hued and long-winged eagles of open country. However, study of genetics have resulted in several reclassifications. These include the moving of smaller, paler and more forest-dwelling eagles in Aquila, the separation of the unique spotted eagles to the genus Clanga as well as the division of some small eagles to the genus Hieraeetus outside of Aquila. Furthermore, genetic research has further revealed a schism in superficially similar eagles between the tawny eagle and its close relatives and other superficially similar Aquila such as the golden eagle (Aquila chrysaetos) species complex. To date, the tawny eagle species group and golden eagle species group are still contained in the same genus despite the apparent lack of close relation.<p>The tawny eagle was previously treated as conspecific with the migratory steppe eagle (Aquila nipalensis). These eagles were considered part of the same species as recently as 1991. The steppe and tawny eagles were split based on pronounced differences in morphology and anatomy. The steppe eagle is a larger bird, with a much more pronounced gape, and differs by appearance in its blockier frame, bigger wings and evinces different coloring at all stages of development, despite some morphs of the two eagles superficially resembling one another. Furthermore, the respective species differ in ecology (dietary biology, nesting habits) and are strongly allopatric in their breeding ground distribution. Two molecular studies, each based on a very small number of genes, indicate that the species are distinct, but disagree over how closely related they are. Genetically, the tawny eagle may cluster more closely with the imperial eagle species complex despite the steppe eagle being more sympatric with those northerly Eurasian eagles.<p>There are three described races of tawny eagles. The subspecific classification of the species has at times been considered complicated by variations and existence of different morphs; in turn they were once considered tentative. However, each subspecies is largely allopatric in geography, the primary ambiguities lying in the northern part of east Africa where both African races may intergrade.

Nome scientifico

Aquila rapax

Autorità

(Temminck, 1828)

Ordine

Accipitriformi

Famiglia

Accipitridae

Genere

Aquila

Areale e habitat

Tawny eagles have an extremely extensive natural distribution. The African population can be found in three, fairly discrete populations. One of these is found in North Africa in south-central Morocco, possibly northern Algeria, southwestern Mauritania, Senegambia, southern Mali, central and southern Niger eastward through southern Chad, northern and central Sudan to most of Ethiopia and Somalia (but for the northeast and central-east). The north African population is scarce. In Morocco, they are heavily depleted with a few populations left in some regions such as Tarfaya, Tan-Tan and Souss-Massa. They are likely extirpated from Tunisia, where they were once frequent. In West Africa, some tawny eagles occur in Gambia, Togo, Nigeria and (though possibly not breeding) in Ivory Coast and Ghana. In east Africa and central Africa, the tawny eagle is found in central and eastern Democratic Republic of the Congo and throughout the drier portions of Uganda and in the entire nations of Kenya, Tanzania, Zambia (quite often residing in the Luangwa valley and the Chambeshi drainage), Malawi and Mozambique. In east Africa, it is considered perhaps the most widely distributed and regularly sighted brown eagle. In southern Africa, the tawny eagle is found throughout Zimbabwe (now often rare apart from Matabeleland and Chipinga Uplands), Botswana (still regular in Okavango Delta) and some areas of Namibia, southern and western Angola (Cuando Cubango, Cunene, Huíla Namibe, to Malanje), Eswatini, Lesotho and northern and central parts of South Africa, i.e. mainly north of the Orange River but sometimes down to the Cape Province. The tawny eagle may be extinct as a breeder in Eswatini where it was last confirmed to have bred in 2001.<p>Out of Africa, the species may possibly be found in the southwestern part of the Arabian peninsula, i.e. in Yemen and extreme southwestern Saudi Arabia in the Tihamah and 'Asir Regions, but few to none confirmed breeding events have been reported in the last few decades. The tawny eagle is considered a rare vagrant in Israel, though some are verified, other reports of them often turn out to be misidentified steppe eagles. They are also known as a rare vagrant in Oman. In Asia, the tawny eagle exists in isolation in southeastern Iran (as in Arabia, verified recent breeding is not known) and somewhat more continuously in eastern Pakistan (often in the Indus valley), much of north and peninsular India, eastward scarcely through southern Nepal and Assam. Though Nepali tawny eagles are rarely recorded, it is thought that the species still resides there in lowland semi-deserts. The Indian range is from Punjab through the Indo-Gangetic Plain and western Bengal, northeastern Bihar, the Deccan Plateau with range continuing down to Andhra Pradesh, Karnataka and (mainly north-central) Tamil Nadu. Records of vagrating tawny eagles turning up in Myanmar, northern Vietnam and Thailand are thought to have been likely misidentified steppe eagles or are based on now unidentifiable specimens. A small handful of vagrants have been verified to turn up in Sri Lanka (the only known appearance by an Aquila eagle there). Old reports of vagrancy, probably in need of confirmation, are known also from Afghanistan.<p>Tawny eagles occurs in fairly open country at varied elevations but usually live in drier areas. In West Africa, the species breeds often in relatively moist forest-savanna mosaics but can move into dry woodlands and semi-deserts when not breeding. In Morocco, the species prefers forested areas near mountains with adjacent plains. Elsewhere in Africa, tawny eagles typically inhabit wooded savanna such as dry Acacia savanna and semi-desert to desert areas. However, extreme desert areas, completely lacking in arborescent growth, are avoided nearly as much so as humid tropical rainforests. It also occurs at times in manmade areas such as arable lands, roadsides, dams, farmland, cattle pastures and game areas if feeding opportunities occur in them. In southern Africa, thornveld is often the preferred habitat with the tawny eagles mostly preferring stands of Acacia. Despite similar climates, within the miombo woodland, the tawny eagle tends to be more scarce. In India, similar habitats may largely be used but the tawny eagle may fairly often occur too in the vicinity of villages and cultivations and frequents garbage dumps and slaughterhouses somewhat more so than they do in Africa. In addition to all gradients of arid zones, in India, the tawny eagle frequently is found around thorn forests. Tawny eagles may live from sea level to about 3,000 m (9,800 ft) but tends to prefer somewhat lower elevations. Despite a certain level of aridity expected in tawny eagle habitats, they normally will not nest unless a habitat meets certain demands. The tawny eagle's presence is predicated on the availability of ephemeral rainfall during the wet season. This reliance on some rainfall is probably key to habitat quality and resulting prey populations to some extent, but also to the availability of nesting sites. The tawny eagle is by and large an obligate tree nester and so areas that become too arid to support tree growth or where trees are overharvested are unlikely to retain the species.

Migrazione

Nomadic movement

Comportamento

The tawny eagle, quite unlike the steppe eagle, is largely sedentary and non-migratory. However, in Africa it is at times considered to be fairly nomadic and can engage in some seasonal movements. In west Africa, A. r. belisarius rather regularly travels shorter distance to damp woodlands during October through November, returning north in April, and perhaps at least at times, migrates into Kalahari region of Botswana and may vagrate to southern South Africa. Sometimes, tawny eagles seem to ping semi-regularly between Ethiopia and west Africa. Some long distance wandering has even been reported, such as a vagrant A. r. belisarius in Tunisia and as far as Egypt (where twice recorded in the 1950s) and even Israel (3 winter records in the 1990s) and Oman. From the Indian range, individuals vagrate not infrequently to nearby Bangladesh, most likely as juveniles post-dispersal wanderings, but reports of the species wandering into southeast Asia such as Thailand are now considered likely apocryphal. Generally, in areas such as southern Africa, tawny eagles usually seldom seem to leave their established breeding territories and juvenile eagles generally wander no more than several dozen kilometres from their original nest. A bird banded as a nestling in Esigodini was recovered quite nearby at Fort Rixon more than two years later. However, in a rather far dispersal for southern Africa, one eagle banded as a nestling was recovered 330 km (210 mi) away from its nest of origin in Zimbabwe four years later. Inconsistent and seemingly unpredictable movements by tawny eagles have been proven via experimental ecological studies to be actually be instances of eagles searching out new areas to compensate for lack of rainfall. While non-breeding steppe eagles are often slightly social and flock at opportunistic feeding sources, the tawny eagle is usually considered solitary. However, groups of two to three tawny eagles are sometimes seen, such as in the Indian subcontinent, but occasionally group sizes may even exceed this figure. In the Mirpur Division of Azad Kashmir in Pakistan, small flocks of tawny eagles have reportedly been witnessed gathering in warmer spots between November and February, over three years of study. Small groups or aggregations are known to occur in Africa as well near concentrated foods and even communal roost have been reported in trees, power pylons or on the ground. Like many large raptors, the tawny eagle probably spends the majority of its day perched but take wing a few times a day. Unlike most large eagles, in India at least, tawny eagles are often fairly accustomed to humans and may allow fairly close approach by observers.

Conservazione

Tendenza della popolazione

declining