Bonelli's Eagle

识别特征

Bonelli's eagle is a fairly large bird of prey and a medium-sized eagle. When still classified as a member of the genus Hieraaetus, it was considered the largest extant species therein, however, as a member of Aquila it is amongst the smallest-bodied species. Amongst the currently accepted species of Aquila eagles, it is of similar size to the tawny eagle (Aquila rapax) (albeit with rather shorter wings than the tawny), slightly larger than the African hawk-eagle and notably larger than the Cassin's hawk-eagle. Like most birds of prey, Bonelli's eagle displays reverse sexual dimorphism as the female is larger than the male to the contrary of most other kinds of birds, in this case she may average about 10% larger overall. Total length in fully-grown eagles of the species can vary from 55 to 74 cm (22 to 29 in). Wingspan in males can vary from 143 to 163 cm (4 ft 8 in to 5 ft 4 in) while that of the female may vary from 156 to 180 cm (5 ft 1 in to 5 ft 11 in). Prior claims put the weight of this species as 1.4 to 2.4 kg (3.1 to 5.3 lb), however this probably slightly underrepresents both their size and the sexual dimorphism of this eagle. A large sample of full grown males from western Europe were found to average 1.94 kg (4.3 lb), with a range of 1.4 to 2.24 kg (3.1 to 4.9 lb) (sample size of 91), while 87 females were found to average 2.62 kg (5.8 lb), with a range of 2.1 to 3.03 kg (4.6 to 6.7 lb). Mature males from western Europe were found to have averaged 65 cm (26 in) in total length and 155 cm (5 ft 1 in) in wingspan while mature females averaged 70.7 cm (27.8 in) in total length and 167.8 cm (5 ft 6.1 in) in wingspan. Although the linear measurements reportedly increase slightly in average size in the eastern Asian part of the range, body weight was similar or slightly lower at a mean of 1.5 kg (3.3 lb) and 2.5 kg (5.5 lb) for males and females from the Indian subcontinent, respectively, though the sample size is unknown in this case. <p>Bonelli's eagles in general form appear to have a medium-sized head on a fairly long neck, a strong bill, a mid-to-longish tail and exceptionally long and well feathered legs. The combination of its well-proportioned, stout body and elongated legs may lend to descriptions of the species as "athletic" in appearance. This eagle often perches with a very upright carriage, at times openly on a rock, a crag, tree branches or some form of post but also in the foliage of tree cover, especially when actively hunting. When perched, the wing tips tend to fall a bit short of the tail tip. Among standard linear measurements, the wing chord of males varies from 458 to 542 mm (18.0 to 21.3 in), with an average in western Europe of 480.4 mm (18.91 in), in tail length from 237 to 287 mm (9.3 to 11.3 in), with an average of 268.1 mm (10.56 in), in tarsus length from 93 to 120 mm (3.7 to 4.7 in), with an average of 99.5 mm (3.92 in) and in total bill length from 40.4 to 45.3 mm (1.59 to 1.78 in), with an average of 43.3 mm (1.70 in). Meanwhile, females vary in wing chord from 478 to 560 mm (18.8 to 22.0 in), in tail length from 246 to 319 mm (9.7 to 12.6 in), with an average of 288.5 mm (11.36 in), in tarsus length from 93 to 127 mm (3.7 to 5.0 in), with an average of 119.1 mm (4.69 in), and in total bill length from 41.3 to 51.8 mm (1.63 to 2.04 in), with an average of 46.6 mm (1.83 in). Two males from the A. f. renschi race measured 444 and 452 mm (17.5 and 17.8 in) in wing chord length and a single female measured 493 mm (19.4 in). Bonelli's eagle is intermediate in its wing lengths and tail length proportionately between the shorter-tailed and longer-winged eagles of open country and longer-tailed and shorter-winged forest eagles, which allows to vary its hunting between short-burst, agile surprise attacks in trees and ample ground-covering pursuits in the open. Its talons and feet are proportionately very large and presumably rather powerful for the eagle's size. In particular the elongated talon on its rear toe (used as a killing apparatus by almost all accipitrids), or hallux claw, is longer than that of the much larger eastern imperial eagle (Aquila heliaca) and proportionately slightly larger even than its bigger sympatric competitor, the golden eagle. Hallux claw lengths in Bonelli's eagles from western Europe averaged 37.21 mm (1.465 in) in males and in females averaged 43.1 mm (1.70 in), and could farther range up to 47 mm (1.9 in).<p>Adult are dark brown above, from a cold hue similar to dark chocolate to an umber hue depending on their state of molt as well as to some extent individual and regional variances, with pale margins to most feathers. These pale margins are especially broad on the median wing coverts (which thus appear lighter brown overall). Adults also have a variably-sized, irregular white patch on the mantle that can vary from nearly absent (though almost never completely so) to being quite large and extending to the upper back. The adult's tail is grey with obscure darker brown thin bars, with a broad blackish subterminal band and creamy white tip. The adult Bonelli's head is dark brown with a paler, often streaky neck and a white throat. The underside has a cream base colour with variable amounts of sparse blackish-brown streaks or drop shaped markings. The adult female averages darker and more heavily patterned than the adult male, particular on the underside, a case of colour sexual dimorphism otherwise seemingly rare in booted eagles. The streaking on this eagle is normally strongest on the breast and upper flanks while the lower belly and crissum are typically either plain or only faintly marked. Juveniles are a lighter medium brown above with variable paler edges, sometimes with a creamy patch on the back (not the mantle as in the adults) and uppertail coverts. Generally, juveniles have a rusty-brown head with a darker brown around and behind their eyes. The juvenile eagle's crown is either darkly streaked or, occasionally, plain greyish. The tail of young birds is more clearly barred than the adults while the subterminal band is only negligibly thicker than the other bars. Like adults, the juvenile Bonelli's eagle's tail has a thin white tip. The juvenile is light rufous to warm buff below with minimal black streaks, which are normally confined to chest-sides. By their 2nd summer, the young eagles are still largely the same in colouring but tend to become more patchy below with increased heavy streaking. During the gradual further development through subsequent molts, the immature eagles develop a thicker subterminal band and a paler ground colour below. Among the bare parts, adult's eyes are yellow to yellow-orange while those of the juvenile are hazel-brown. Adult plumage is obtained between the 4th and 5th years. At all ages, the cere and feet are both pale yellow.<p>In flight, Bonelli's eagle is a largish raptor with a well projecting head and broad, long and somewhat square ended wings which are slightly pinched in at body with a little tapering at tips. Feather molts can make the wings look quite variable in shape with some individuals appearing rather longer and narrower winged than others. In flight, the tail appears long and broad but if pinched in can appear surprisingly narrow. This species tends to fly with powerful but loose shallow beats. When gliding, they do so often on flat wings with well-spread feathers and the carpals pressed slightly forward but more so when entering a fast glide. This species soars infrequently on flat or slightly raised wings. At nearly all times of the year, Bonelli's eagles quite often flies in pairs. In colouring, the flying adult is dark above with a variable amount of the white marking on the mantle. The tail has faded barring (rarely perceptible) on grey with a big blotchy subterminal band and a white tip above. The markings on the tail look more or less the same when seen both from below and above. Adult Bonelli's eagles have white lesser coverts which along with the greyish tail stand out in contrast against blackish central wing band over the greater and median coverts. Also the flight feathers are faintly and thinly barred light grey-brown with paler bases, which often become paler (to a whitish hue) on the primaries inside blackish tips and leading wing coverts. In flight, juveniles are brown above with slightly darker wing ends and tips to greater coverts and greyer primary windows. Occasionally, juveniles manifest a creamy patch on back and obscure narrow U above barred tail, which even if present are only sometimes visible. Below the juvenile's wing linings are light rufous to warm buff like the body colour. Usually juveniles appear with darker tips to greater coverts forming wing-diagonals (sometimes lacking or confined to carpal area) and a small but distinct area of white on primaries against the blackish tips. Until the 3rd year, the young eagles appear more like a 1st year juvenile than an adult, but begin developing more streaks below and darker greater underwing coverts. By the 4th year, the subadult Bonelli's are increasingly similar to the adult, with an increasing subterminal band, a whiter underbody and fairly prominent underwing-diagonals. However, subadults are often still appear with a mix of paler barred juvenile type feathers and plainer darker adult feathers on the flight feathers.<p>Bonelli's eagles are generally unmistakable when shape, flight and plumage are considered in combination. In poor light, it is possible to mistake one with a honey buzzard, one mainly in Europe and another mainly in Asia, as these raptors are extremely polymorphic and can come surprisingly close to approximating the plumage of various more powerful raptors. The wing shape in Bonelli's eagles can at times appear similar to that of honey buzzard but the latter raptor type are usually distinctly slimmer and slighter bodied with a much smaller, slimmer head. In flight, honey buzzards often have notched rather than square ended tails, less emarginated primaries and typically they fly with their wings held more at an angle. The sympatric species of honey buzzard tend to have bolder barring on the tail and underwings, broader dark trailing wing edges and all have no pale mantle patch or darker underwing-diagonals. An unlikely source of confusion is the northern goshawk (Accipiter gentilis), which is usually visibly smaller with much shorter wings, a slightly longer tail, different level flight style and many distinctive plumage characteristics. Distant juvenile Bonelli's could conceivably be mistaken for the long-legged buzzard (Buteo rufinus), but the buzzard is also smaller and is shorter tailed with prominent dark carpal patches and dark trailing wing edges. Furthermore, the buzzard usually holds its wings in a noticeable dihedral when flying in a soar. Another unlikely confusion species is the short-toed eagle (Circaetus gallicus) which roughly matches the size of Bonelli's eagles but the short-toed has larger and differently rather wedge-shaped wings with a much less dark overall pattern as well as a shorter tail, a rounder head on a shorter neck and usually a dark rather than light throat. Also, goshawks, short-toed eagles and European honey buzzards usually frequent different habitats, more often living in more wooded and lowland habitats. Bonelli's eagles may be mistaken for pale morph adult booted eagle (Hieraeetus pennatus) by inexperienced observers but, beyond being a third larger and more than twice as heavy, Bonelli's eagles are moreover distinct in plumage. Overall Bonelli's are much darker and streaker especially compared to the clearly paler flight feathers of booted eagles. Booted eagles are both whiter and more contrasting on the upperwing coverts, have whitish uppertail-coverts and have white on the wing's patagium. More similar in plumage is the juvenile Bonelli's eagle are the rare rufous morph of the booted eagle but the latter can still be told by the booted species' narrower wings and smaller size. In southern part of the Red Sea, vagrants (largely juveniles) may possibly come into range of the closely related and more similar African hawk-eagle, but the latter is somewhat smaller and comparatively short winged and longer tailed (the total length is similar between the species due to the African's longer tail but Bonelli's can be visibly larger bodied and rather heavier). In the African species, the adult plumage is a more contrasting, with dark slate gray upperparts, purer white underparts with dark streaking. In African hawk-eagles, juveniles compared to Bonelli's are darker above with pale wing-windows.<p>Bonelli's eagle is largely silent outside of breeding season and is a somewhat infrequent vocalizer even in the context of breeding. Its calls are less well studied than those of the African hawk-eagle, which although a tropical species, also generally ceases to call outside of the breeding season. The main call of Bonelli's eagle is done during the courtship display and, sometimes, also at the nest. Its main call consists of a loud, shrill, somewhat far-carrying scream, yuiii-yuiii-gii-gii or a drawn-out heeeeii-heeeeii with slight regional or even individual variations. Its call is farther carrying than the "puppy-like" one of the golden eagle and is reminiscent in pitch of that of the red-tailed hawk (Buteo jamaicensis). The call may be given by both sexes. However, the female Bonelli's eagle calls most intensely when the male is delivering prey unlike the preference for vocalizing in aerial display as the male usually does. Other recorded vocalizations have included a fluted, low-pitched klu-klu-klu as well as a repeated ki ki ki in alarm. Also other barking, gurgling and grunting sounds have been reported by researchers at or near the nests.

分类信息

Bonelli's eagle was described in 1822 by French ornithologist Louis Pierre Vieillot. The common name Bonelli's eagle is for the collector of the type specimen, Franco Andrea Bonelli. Bonelli's eagle is a member of the Aquilinae or booted eagles, a monophyletic subfamily of the accipitrid family. At least 38 species are currently housed in the subfamily, all with signature well-feathered tarsi. The African hawk-eagle (Aquila spilogaster) was once lumped with Bonelli's eagle, with most accounts until about the 1990s listing the species as monotypical. However, several morphological differences between the two species, life history discrepancies and their considerably allopatric distribution lead them to being considered separate species. Despite the differences between Bonelli's eagle and the African hawk-eagle the two species are visibly similar and are still considered sister species. However, genetic studies have indicated that they are not closely related relative to other species pairs of the booted eagle subfamily. Recent DNA research resulted in the two species being moved, in 2014, to the genus Aquila from Hieraaetus, along with another dissimilar 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). These species are all conspicuously larger than Bonelli's and African hawk-eagles with differing proportions to their wings, tail and legs (in adaptation to their open country habits) and much darker coloured plumages. Furthermore, the four other traditional members of the genus Aquila have been revealed to be a separate species complex despite showing superficial similarity to the golden eagle group, i.e. being relatively large and long winged with usually dark coloring. Beyond the nominate subspecies of Bonelli's eagle, which is found throughout its range in Eurasia, a second subspecies dwells in the Lesser Sunda Islands, A. f. renschi. The latter race is linearly smaller, and compared to other Bonelli's eagles tends to have more strikingly barred remiges and tail, the belly, thighs and crissum more boldly marked. At one time, its restricted and very isolated range have caused authors to suggest A. f. renschi may be a full species but recent studies have indicated that it is not genetically distinct enough to be considered a separate species. Furthermore, the most recent analysis couldn't rule out early introductions (possibly by ancient falconers) at least playing a part in the species presence in the Lesser Sundas, as some other established wild birds on those islands are certain to have reached there by early human introductions.

学名

Aquila fasciata

命名信息

Vieillot, 1822

目

Accipitriformes

科

Accipitridae

属

Aquila

分布与栖息地

Bonelli's eagle have a spotty and sparse worldwide distribution currently. The species is distributed in northwestern Africa from the Anti-Atlas in Morocco northeasterly through the lower parts of the Atlas mountains in northern Algeria and northern Tunisia (and probably formerly northern Libya). Beyond its African breeding range, the IUCN and others have mapped out a semi-regular wintering range for Bonelli's eagles, in coastal west Africa from southern Morocco down through Western Sahara, Mauritania and northwestern Senegal (rarely also east to Mali), although little more is reportedly known about this population and its origins and altogether the species is considered largely non-migratory. Additionally, the species has been recorded as a vagrant in east Africa in Somalia as well. <p>In southern Europe, they range patchily through different parts of Portugal and Spain into southern France as far north as the department of Drôme. Discontinuously, they are now seemingly solely left as breeding bird in Italy on the islands of Sardinia and Sicily. They at least were known to live in Aspromonte National Park in Calabria, near the far southwestern tip of the Italian peninsula, directly across the narrow Strait of Messina from Sicily. In southeastern Europe, an isolated population possibly persists in Croatia as well as in northern and southern Macedonia (with the further possibility of spilling over into Kosovo) and spottily through different areas of Greece (possibly spilling over the borders in the west in Albania and in the east in Bulgaria), as well as Crete. <p>Out of Europe, they may be found in western and southern Turkey, Syria (possibly but most likely extirpated), the isle of Cyprus, Lebanon, Israel, western Jordan, northeastern Egypt (rarely in northern half of Sinai Peninsula), possibly but not certainly in spots in the west and south of Saudi Arabia, and elsewhere in the Arabian Peninsula to Yemen, Oman, and the United Arab Emirates. Elsewhere in the Middle East, their range includes eastern Iraq and west, south, and northeastern Iran, extending somewhat into Turkmenistan in the Kopet Dag range.<p>Further east into Asia, their distribution includes eastern Afghanistan and Pakistan through most of the Indian subcontinent, where generally it is uncommon but more locally common near Nepal. On the other hand, they are absent in eastern India and only occur as a vagrant to Sri Lanka and Bangladesh. In India, they are most regularly found in areas such as the Chambal ravines, Ranthambore National Park, the Chir zone of the lower Kumaun Himalayas, and in winter in the Keoladeo National Park of Bharatpur, Rajasthan. From central Myanmar, they range across into northwestern Thailand and northern Laos (though possibly only as a visitor rather than breeding in the latter two). In southern China, their resident range includes Yunnan, Guangxi, and Guangdong north to the Yangtze river, as well as rarely into Hong Kong. Their isolated Indonesian population range is in the Lesser Sunda Islands, including at least Sumbawa, Timor, Wetar, Luang, and Flores, however records show they've turned up on as many as 20 islands in the Lesser Sundas.<p>Historically speaking, research published in People and Nature in 2024 by scientists from the University of Granada and Miguel Hernández University of Elche (UMH) indicates that Bonelli's eagle is a relative newcomer to Europe and the Mediterranean Basin and that they spread there with the help of humans around 50,000 years ago. Genetic analyses indicate that the Mediterranean Bonelli's eagle population likely comprised a few individuals around the last glacial maximum, which later thrived as the temperature in the Mediterranean Basin rose, and the human population grew and became sedentary.<p>Mechanistically, the three bilateral interactions among Bonelli's eagles, golden eagles, and the human population are jointly what allowed Bonelli's eagles to move from the Middle East into the Mediterranean Basin at this time – and also what prevented them from moving there sooner. Golden eagles are less tolerant of humans than Bonelli's eagles are. Additionally, between the two eagle species, the golden eagle is the dominant species, while Bonelli's eagle is the subordinate one. With these interactions in mind, the authors of the 2024 People and Nature study hypothesize and test with data-driven mathematical models that with the arrival of the first anatomically modern humans in Europe, some of the golden eagle territories closest to human settlements were abandoned, and these 'vacant' territories began to be occupied by Bonelli's eagles from the Middle East. That is, Bonelli's eagles could not have established themselves in the Mediterranean before the arrival of the first Homo sapiens because the competitive pressure exerted by golden eagles and other species would have been too overwhelming, but the arrival of humans displaced the golden eagles and provided an empty niche in the localities' ecosystems that Bonelli's eagles were then able to neatly fill.<p>Bonelli's eagles are mostly residential throughout their range but juvenile can disperse up to over several hundred kilometers. Sometimes, they are recorded at migration sites and at spots where not known to breed in winter. Wanderings include around 700 km (430 mi) north of their regular range in France near the coast of English Channel, far from their normal haunts in Regensburg, Germany and, probably both from the Italian island populations, to northwestern Italy and Slovenia. From their Iberian peninsula range presumably, vagrants have been reported in the Canary islands. Beyond Sri Lanka, other areas the species has been known to vagrate (or perhaps rarely winter) in Asia have included Kazakhstan, the Korean peninsula, Malaysia and Cochinchina in Vietnam, as well as a record in winter 1996 on the isle of Yamdena, the latter presumably from the Lesser Sunda population.<p>The Bonelli's eagle tends to dwell in similar habitat types across its range and lives in lands hugging large bodies of water, largely the Mediterranean Sea and northern Indian Ocean. To a lesser extent, it lives near the coast of the Atlantic and the Pacific Oceans and near the Caspian Sea. Despite often being near seas and oceans it mostly occurs in fairly arid habitats and in quite sunny areas. It prefers rocky areas including lower mountains and foothills with plentiful cliffs, as well as steep sided canyons and is very skilled at hunting in craggy, irregular rocky terrain. Usually, extensive garrigue-type habitat such as low bushes or more substantial vegetation such as scattered trees are a common feature of residential ranges but also at times even denser woodlands. Such scrubby areas are key since they hold prey concentration in Mediterranean habitats. However, excessive ground cover may limit hunting success so scrub is avoided when it becomes too dense. In the Mediterranean region, forests visited by Bonelli's eagles are usually either pine forests or sclerophyll forests. Deep forests are generally avoided, however. Although Carrascal &amp; Seoane (2009) claimed that agricultural areas are generally avoided per their analysis in Spain, Martinez-Miranzo et al. (2016) indicated that the species was showing a growing preference for agricultural arable land and other human-modified habitats, probably as prey selection has shifted more heavily to pigeons out of necessity. A similar growing preference for arables was also detected in Sicily as well. However, urban areas are generally strongly avoided both as breeding and as foraging areas by this species. Bonelli's eagles may additionally range into timbered plains or even virtually barren slopes or semi-desert, especially in areas such as Israel and India where moister valleys intersect with deserts. Juveniles may take up temporary residence over dry cultivation, small wetland areas, coastlines or surprisingly deep woodlands. In winter, these eagles may occur at times at lower elevation levels and more open habitats in semi-deserts and plains, where they can appear surprisingly at home, but often prefer wetter habitats such as large river mouths, marshlands and lakes, especially where these fall in existing home range, as prey is more likely to be concentrated in such areas. In some areas such as southeastern Asia, some of the Indian subcontinent and in the Lesser Sundas, Bonelli's eagles may reside around tropical rainforest that is much wetter and more humid than their typical habitats, and in such areas are attracted to more sparse and rocky areas such as slopes and cliffs as well as alternately open mosaics and glades. Usually Bonelli's eagles live at an elevation of 1,500 m (4,900 ft) or lower in Europe, to 2,000 m (6,600 ft) in their African Atlas mountain homes and to as high an elevation 3,000 m (9,800 ft) in Asia and even 3,750 m (12,300 ft) in residence in Bhutan. The main elevation where the species resides in the Himalayas falls between 1,200 and 2,000 m (3,900 and 6,600 ft).

迁徙

Resident species

保护状况

种群趋势

declining