Studies of Less Familiar Birds 161 Booted Eagle R

Studies of less familiar birds 161 Booted Eagle R. F. Porter Photographs by Pierre Petit, M. D. England and A. N. H. Peach Plates j 2- j 8 The Booted Eagle Hkramtus pennatus is a small eagle similar in size to a Buzzard Buteo buteo, but of slimmer build, with narrower wings and a longer tail. In flight its proportions are not unlike those of a Black Kite Mikus migrans, though the tail is square-ended, not forked (plate 58). When perched, its long feathered tarsi, or 'boots', are characteristic (plate 53b). The species is dimorphic, a feature which, among European birds of prey, it shares only with Eleonora's Falcon Fa/co eleonorae. Many raptors show considerable plumage variations, but in most cases these take the form of clines from very pale to very dark through a whole range of intermediates. The Booted Eagle has two very distinct phases—a light and a dark. This dimorphism is exhibited by both sexes; breeding pairs frequently consist of one dark and one light and their offspring may be either light or dark. Both phases are brilliantly illustrated in plates 52-58. The light phase has a lightly streaked tawny-rufous head and neck, with a white forehead and superciliary stripe and dark tawny-brown ear-coverts and cheeks. The under-parts are white with rufous streaks on the chin, upper breast and flanks (plates 5 5 a and b), and the under wing-coverts are also white with brownish flecks (plate 5 8b). Im- matures look more 'gingery' below. The white under-parts extend on to the 'shoulder' to form a white patch (especially plate 5 2). The mantle and back are dark brown, with blackish primaries and secondaries, and there is a conspicuous broad bar of pale huffish-brown on the upper wing-coverts and scapulars, giving the upper-parts the appear ance of a well-marked Black Kite (plate 52 again). The upper tail- coverts are pale buffish-brown, contrasting with the brown back and brown tail; the latter is faintly barred with grey. The under tail- feathers are white with a varying amount of dark smudgy grey on the tips, particularly of the central feathers. The upper-parts of the dark phase (plates 54a and b) are similar to those of the light phase, but the under-parts (plates 54c and 55 c) are wholly dark brown, streaked with black, though the bases to the primaries are paler brown and the under-tail is also paler, frequently taking on an orange tinge. The white shoulder-patch can occasionally be discerned in the field (plates 54a and 5 5 c), In flight at long range, light-phase Booted Eagles show a conspic- 353 334 Booted Eagle studies uous under-wing pattern of white forewings contrasting with black flight-feathers, not unlike the pattern of an adult Egyptian Vulture Neophron percnopterus (plate 5 8b); despite their differences in shape and structure, I have seen these two species confused more than once. Dark-phase birds can be more easily overlooked, particularly among flocks of Black Kites. To some extent they also resemble brown Marsh Harriers Circus aeruginosus, though the wing position when soaring is quite different: the Booted Eagle holds its wings level, not in the shallow ' V of the harrier. From beneath, both phases show a paler area on the inner primaries and outer secondaries (plate 5 8), but a much more elusive character (just discernible in plates 58a and 5 8d) is the translucent whitish trailing edge to the wings and tail, sometimes visible when overhead in bright sunshine. The wing-beats are deeper and more floppy than those of Buz2ards and are interspersed with glides on level wings. The breeding distribution of the Booted Eagle was described in detail by Vaurie (1965) and Dementiev and Gladkov (1966). In western Europe it is confined to Spain, Portugal, central and north-east France and the Balearic Islands, and in the east to Hungary, Jugo slavia, Albania, northern Greece, Bulgaria, Romania and European Russia almost as far north as Moscow. Its range extends along the north coast of Africa from Morocco to Tunisia, and in southern Asia from Turkey, northern Syria and the Caucasus through northern Iran to Afghanistan and north-west India, as well as the Turkmen, southern Uzbek, Tadzhik and Kirghiz Republics north-east to the region of Lake Balkhash. In central eastern Asia it occurs again in the northern Altai Mountains, northern Mongolia, the Sayan Mountains and the Irkutsk region eastwards beyond Lake Baikal to northern Manchuria. Thus this eagle is distributed in three main regions: western Europe and north-west Africa, eastern Europe and southern Asia, and northern Mongolia and the Lake Baikal area. At its broadest the range extends south to 55°N and north to 5 j°N. Systematists differ on the degree of subspeciation involved over this range of 7,000 miles from west to east. Vaurie (1965) treated the species as monotypic, but B. Stegmann (Orn. Monatsber., 43: 151) separated the population of southern Siberia and northern Mongolia as H. p. harterti (with which H. p. milvoides and H. p. albipectus are synonymous). Brown and Amadon (1968) also split the species into two races. Whatever the conclusion, the fact remains that Booted Eagles in the east of the range are longer-winged and migrate to Malaya, Burma and India, while those in the west migrate to north east and tropical Africa. There does not appear to be any clear geo graphical distribution of the light and dark phases throughout the range (Dementiev and Gladkov 1966), though there is a tendency to find a higher ratio of dark birds in the east. From observations of Booted Eagle studies 335 migrants in Turkey, and in particular at the Bosphorus, it would appear that the Booted Eagles of eastern Europe are largely of the light phase (of the order of 75 %). As with nearly all raptors, the Booted Eagle is decreasing in numbers. In France the population has been estimated at only 30 to 50 pairs and steadily decreasing; in Portugal it is 'scarce' and in Spain 'thinly spread' (I.C.B.P. 1964). At the Bosphorus 260 migrants were counted between 1 ith August and 9th October 1966, and similar totals in 1967, 1968 and 1969; a century ago, however, A. Alleon and J. Vian recorded flocks of several hundreds passing in rapid succession (Porter and Willis 1968). In Russia Dementiev and Gladkov (1966) recorded a decline in the population of the Kharkov region and indicated that changes in habitat were responsible. The breeding areas include deciduous or coniferous woodland from well-forested areas to scattered clumps of trees and from sea-level up to 10,000 feet. The preferred habitat, however, seems to be wooded slopes with open glades and adjacent open or cultivated areas in the foothills of more mountainous regions. Forest clearance throughout Europe and Asia must have had an adverse effect on the population. In addition, the habitual shooting of birds of prey throughout much of their range, particularly in the countries through which they migrate, must have taken a considerable toll. In the three countries of western Europe where Booted Eagles nest—Spain, Portugal and France—the species is not protected. Even if protection were afforded to it, enforcement would be impossible without protection of all other birds of prey, for how many members of the shooting populace could distinguish between, say, a Buzzard and a Booted Eagle? On migration in Europe, Booted Eagles can be most easily observed at the Bosphorus and Gibraltar. Spring migrants start to arrive in late March and the peak generally occurs in the first two weeks of April, though migrants (possibly non-breeding birds) can still be seen on passage in late May. In autumn the peak occurs in the middle weeks of September, and at the Bosphorus it coincides with the peak passage of Lesser Spotted Eagles Aquila pomarina and Buzzards. In both spring and autumn my own observations have been of single birds, or occasi onally of groups of up to three. In Europe Booted Eagles start to take up their territories in mid- April. As with most birds of prey, the nuptial display-flights are spectacular and the birds are then extremely vociferous. Booted Eagles which I watched in Istanbul's Forest of Belgrade were far more active and spent longer on the wing than the other nesting raptors of the area. The most frequent display consists of a series of steep undu lations with the wings held close to the body. This is performed by both sexes and the position adopted is similar to that in plate 58c, which shows one diving towards its prey, in this case a sparrow 336 Booted Eagle studies Passer sp. Sometimes one of the pair turns on to its back in mid-air and presents upstretched claws to its mate. During these nuptial aerobatics the call I have heard is generally a rather querulous kvee-kvee- kvee, uttered by both birds, though clearly from Dementiev and Gladkov (1966) and Brown and Amadon (1968) there are many variations of this. Both at the breeding grounds and on migration, their great agility and rapid manoeuvrability are seen at their best when being mobbed by or mobbing other birds, particularly raptors, and one gains the distinct impression that Booted Eagles indulge in these aerial forays as much for their own sake as in guarding a territory. When being mobbed, the bird may rapidly gain speed with deep, powerful, wing-beats and then suddenly roll over sideways flinging its talons into the air at its pursuer.

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