J. Yamashina Inst. Ornith., 14: 108-121, 1982

The Genera of Booted : and Relatives*

Dean Amadon**

Abstract The nine genera of eagles with feathered legs (hence "booted") are reviewed. Of the nine, six were monotypic. One of the six, Ictinaetus, is very distinct and is probably not a member of the group. Of the other monotypic genera Polemaetus is here combined with , and Lophaetus, Oroaetus, and Stephanoaetus with . The remaining mono- typic , Spizastur, is for the time being retained because, while very close to Hieraaetus in characters, it may in fact prove to be a New World offshoot of Spizaetus stock. The genus Aquila with 10 is left as presently constituted. All of the five genera recognized are diagnosed; their way of life briefly characterized, problems at the species level discussed, and the species of each listed in a recommended sequence.

Introduction

The term "booted" is applied to a group of about thirty species of eagles, so called because their legs (tarsi) are feathered down to the bases of the toes. In most current literature (e.g. Stresemann & Amadon 1979) they are divided among nine genera of which no fewer than six are monotypic; the best known of the genera is Aquila whose is the well known Golden , A. chrysaetos. Feathered tarsi occur sparingly elsewhere in the family , for example in the "Rough-legged" Hawk, lagopus; the condition is of no particular taxonomic significance in and of itself. In the hawk mentioned, and also in such as the Snowy (Nyctea scandiaca), not to mention ptarmigan (Lagopus), feathered legs are clearly an adaptation to withstand arctic cold, but in the there is no diminution of the feathering in tropical species; conceivably it gives the legs a little additional protection when grappling with dangerous prey. The Indian , Ictinaetus malayensis, which comprises one of the monotypic genera, is a peculiar species in many respects, as detailed later. The genus is clearly valid and may not belong to the same group as the other booted eagles, albeit that the tarsi are feathered, though somewhat thinly. The remaining eight genera, five monotypic, give every appearance of being a monophyletic, closely and intricately interrelated group. A generic reassessment seemed appropriate. In the following analysis each of the genera recognized is followed by a list of the included species. To the extent that it concerns the genus composition, problem taxa- those on the -species border are discussed. Original citations for species names may be found in Stresemann and Amadon (op. cit.).

* Dedicated to my friend Dr . Yoshimaro Yamashina, Pre-eminent Leader of Ornithology in Japan for Half a Century. ** Lamont Curator of , Emeritus; American Museum of Natural History, New York, USA 10024.

108 Genera of Booted Eagles 109

Methods

Generic diagnoses for the booted eagles are presented, somewhat informally, in Brown and Amadon (1968). Two of the genera, Aquila and Hieraaetus, are defined in Glutz et al. (1971), based in part on the earlier monograph by Hartert (1913-1914). Hartert also treated Spizaetus, but only briefly and for some reason he separated it from its closest allies. Voous and Wijsman (1964) discussed the generic characters of the booted eagles, especially the African ones. Other references are mentioned below. For only one of the species of the group is the term "" used as a vernacular name, viz., Hieraaetus pennatus of Eurasia and . I have twice been responsible for generic treatments of the hawks and eagles so it is reasonable to ask why the changes recommended below were not made previously. Further study in field and museum seemed advisable before doing so. Stresemann and Amadon (1979) is based on an earlier manuscript list by Stresemann and I did not wish to make further reductions in his genera beyond those that seemed essential, as summarized on page 272 of that list. Actually, as there pointed out, Stresemann had himself synonymized one genus of the group under consideration, Lophaetus, a course which I then resisted as it did not seem logical to merge this genus without further consideration of several others. I have observed seven of the nine currently recognized genera in the field; all except Oroaetus and Ictinaetus. Of species, I have observed: Aquila-chrysaetos, verreauxii, rapax, nipalensis, wahlbergi, audax; Spizaetus-ornatus, tyrannus; Hieraaetus-spilogaster, ayresii, morphnoides, and also the single included species of Stephanoaetus, Lophaetus, Spizastur and Polemaetus. It is now conceded that many genera must be defined by a suite of characters not all of which will be found in every included species, although every species will possess a preponderance of them. This is certainly true of the three polytypic core genera of booted eagles Aquila, Hieraaetus, and Spizaetus. They are difficult to diagnose, yet seem to be natural monophyletic units. The paucity of trenchant morphological characters among birds, the result of loss and fusion of skeletal elements, including teeth, is well known. Yet avian genera are often the equivalent of those of other classes of higher as regards antiquity, number of included species, and ecological distinctness. Mensural characters: The genera of booted eagles are separated to some extent by relative length of wing, tail and sometimes tarsus, though there are species whose measurements agree with one genus and its other characters with another, e.g., Aquila gurneyi. Wing and tail proportions are here expressed as the ratio of tail to wing as a decimal; for example in most species of Aquila the tail is about half the wing or .50. Obviously this is a very rough measure which may be affected either by a lengthening or shortening of wing or of tail or of both in any particular taxon. Thus in the genus Spizaetus the tail is relatively long and the wings relatively short and rounded to produce proportions like those of a classical "hawk" (Accipiter); the name "hawk-eagle" refers to this. There are correlated changes in the shape of wing and tail: the longer the tail the more apt it is to be rounded or even wedge-shaped; the relatively shorter the wings, the 110 D. Amadon

more rounded and broader they are. Ratios of tail to wing given in this paper are based on the wing measured "flat"; the shorter chord measurement, of course, gives a slightly higher ratio. The relative length of the tarsi varies considerably in all the polytypic genera recognized here from species to species. In general, large species that strike heavy, powerful prey have short tarsi and heavy talons. In the African Long-crested Eagle, Spizaetus occipitalis, the legs are especially long, presumably because it strikes at concealed in rank grass. A species' overall or general size is not usually considered a valid generic character in these or other birds. There was already a wide range in size between for example Spizaetus nipalensis orientalis and S. nanus or between Hieraaetus f. fasciatus and H. morphnoides weiskei. Thus adding Stephanoaetus coronatus to the former and Polemaetus bellicosus to the latter genus does not greatly extend the range of variation in size, at least in Spizaetus, where the wing length of coronatus does not much exceed that of the Japanese subspecies of nipalensis, though it is a heavier . The measurements used in this paper to calculate ratios were taken directly from specimens or from standard sources such as Brown & Amadon (1968). Synonyms listed under the generic headings include only those having different type species.

Relationships of the Booted Eagles to other Eagles

The term "eagle" is applied indiscriminately to any especially large hawk. Among other groups so designated are the sea-eagles, the serpent-eagles and the harpy eagles. The booted eagles differ in so many ways from the sea-eagles and the serpent-eagles as to require no detailed comparison with them. On the other hand the resemblance of such a booted eagle as the African ("Stephanoaetus") to the (Harpia harpyja) in proportions, way of life, and even in the prolongation of the nesting cycle over two years, leads to recurring questions as to whether the two groups may be more closely allied than is generally supposed. The harpy group includes also Morphnus, which is much like Harpia, and two relict Old World genera, Pithecophaga in the Philippines and Harpyopsis in New Guinea. These four monotypic genera comprise a somewhat primitive group, allied with what I call the sub-buteonine hawks and eagles (Brown & Amadon 1968, Amadon 1982). Their long unfeathered coarsely scaled tarsi are only one of several characters separating them from the booted eagles. They are somewhat less advanced, albeit specialized, relatives of the stem genus Buteo, while the booted eagles are more advanced and stand at the apex of the family Accipitridae, along, perhaps, with such "modernized" and cosmopolitan genera as Circus and Accipiter, with Buteo itself only a shade below them. The genus Buteo thus forms a standard of comparison between the harpy group on the one hand and the booted eagles on the other. Osteologically, Buteo and Aquila are said to be extremely similar. As to the living species comprising the two genera, however, there is not one that calls for the slightest hesitation in generic placement. Genera of Booted Eagles 111

Relevance of

Eventually comparison of fossils will aid in classifying the living booted eagles but as yet the material is so scanty and fragmentary as to be of little help, especially since the living forms are very closely and intricately related to one another. A few fossil forms have been assigned to living genera but, with the exception of some forms such as the Golden Eagles of the California tar pits (Howard 1947), without good comparative osteological material. Brodkorb (1964) in his check-list of fossil birds recognized a genus Aquilavus with five species, all from the Upper Eocene or Lower Oligocene of . Four of the five were originally placed in the genus Aquila which would indicate that Aquila-like stock has been in existence for a long time. A fossil from the of France is assigned to Hieraaetus and another from the same period and area to Aquila. Three species from the Pleistocene of western North America have been placed in Spizaetus. Around the world in , Pleistocene bones have been assigned to the contemporary Aquila audax. One may conclude that stock similar to the booted eagles of today has been around long enough so that the present absence of two of the three stem genera from the Nearctic Subregion poses no zoogeographical problem. As noted, Spizaetus, or something very similar to it, was present there in the Pleistocene. In Eurasia, the occurrence of a living Spizaetus in Japan suggests that the genus was widespread, and was stranded in Japan when other taxa adapted to warm climes retreated south during the glacial epochs. There are of course other elements in the Japanese biota of which the same is true.

Genus Ictinaetus

Ictinaetus Blyth, 1843, Jour. Asiatic Soc. ., 2: 128. Type: Aquila pernigra Hodgson.

Diagnosis. Inner toe very much shortened in relation to the others; talons weak and almost straight. Wings and tail large in relation to the slender body. Remarks. The peculiar Black Malay Eagle, despite its thinly feathered tarsi, probably does not belong to the booted eagle group; in any event it is a very distinct genus. Sushkin (1899), on the basis of its anatomy and the peculiar immature , thought that it may be a specialized offshoot of the Milvine kites. The light wing loading enables it to soar slowly at treetop level above the jungle and snatch and young birds from . The shortened inner toe and almost straight claws permit it to do this without snagging its foot in the nests. Other hawks that snatch much of their prey from nests or narrow cavities also have a shortened inner toe to make the foot narrower; the genera in question are Polyboroides and Geranospiza (Amadon 1982). Species. 1-malayensis.

Genus Aquila

Aquila Brisson, 1760, Orn., 1: 28, 419. Type: Falco chrysaetos Linn. Pteroaetus Kaup, 1844, Class. Saugeth. und Vogel, 120. Type: Aquila verreauxii Lesson. Uroaetus Kaup, 1844, ibid.: 121. Type: Vultur audax Latham. 112 D. Amadon

Psammoaetus Roberts, 1924, Ann. Transvaal Mus., 10: 80. Type: Aquila nipalensis Hodgson. Afraetus Roberts, 1924, ibid; 80. Type: Aquila wahlbergi Sundevall; new name for Micraetus Roberts, 1922, preoccupied.

Diagnosis. From Buteo differs by larger size; heavier legs and talons; relatively larger , prevailingly darker coloration with usually less contrast between immature and adult . Maturity at three years or older, at least in larger species; molt of primaries irregular. As compared with Hieraaetus, Spizastur and Spizaetus: bill relatively larger, with culmen more or less straight near base, then decurving. Rear talon usually relatively shorter except in the largest species (chrysaetos, verreauxii, see fig. 1 in Brooke et al. 1972). Tail usually relatively shorter, about .50 of wing. No crest, except a short one in A. wahlbergi. Coloration more uniformly dark, with little or no barring of wing and tail quills and with immature usual plumage more like that of adult. Nape often lanceolate, sometimes bronzy or golden in hue, hence "Golden" Eagle, A. chrysaetos, the type of the genus. Immatures in general are quite similar to adults, but with some white, fulvous or brown markings on body and sometimes at the bases of the wing quills. Acquiring full adult plumage may take four or five years or perhaps longer in these large species. The species of Aquila are accomplished soarers, the wings long, moderately broad, sometimes narrower near the body in the area of the secondaries (verreauxii), with the outer five or so primaries strongly incised on their inner vanes. The tail is of moderae length, about .50 of wing length and slightly rounded; the aberrant, tropical--frequenting A. gurneyi, has relatively shorter wings and longer tail (tail/wing ratio about .62). The larger species of Aquila prey chiefly upon , occasionally up to the size of a small ; A. chrysaetos also catches some birds, even in flight. Most of them take in times of stress, and A. rapax takes much carrion and also robs other birds. The smaller species catch some and amphibians and even the large A. nipalensis feeds upon emerging . Courtship is usually not noisy or conspicuous. A large stick is constructed; in trees by some species, on cliffs by verreauxii and in either situation by others. Two or three eggs are laid but in some species sibling antagonism is extreme (verreauxii, pomarina) and only one chick survives. All species are capable of breeding annually. The Australian A. audax has a wedge-shaped tail and for that reason was placed in a monotypic genus, Uroaetus. This species seems close to the type of the genus A. chrysaetos, or perhaps, judging from its juvenal plumage, to A. verreauxii (C. White, verb. comm.), and no one has recognized Uroaetus recently, except inadvertently as in Rand & Gilliard (1967). Wahlberg's Eagle (wahlbergi) is rather aberrant and to some extent intermediate towards Hieraaetus. Brown (in litt.) wrote that it differs from the larger species of Aquila "in its whistling , not barking, yelping or clucking voice; it is crested, very small, flies with rapid wingbeats, has a very different flight silhouette to most Aquila•c and almost invariably lays (but) one ." Its tail relative to the wing is a little longer than in most

aquilas; ratio about .55 as compared with .50. Nontheless wahlbergi is in essential features an Aquila and it is unnecessary to resurrect Roberts' name Afraetus for it. Genera of Booted Eagles 113

Gurney's Eagle, gurneyi, of Papua and nearby islands is also atypical, in its long, somewhat rounded tail and relatively short wings. Presumably it spends more time in forest than the typical aquilas; indeed it is the only member of its genus characteristic of areas which are predominantly covered with forest. Because of its proportions gurneyi, though correctly described in Aquila, has sometimes been placed in Spizaetus, but this is surely an error, as pointed out by Jollie (1957). That inveterate genus-splitter, Roberts, provided a name, Psammoaetus, for the Eagle, A. nipalensis, known to him as a migrant in Africa. This eagle and its close relative, A. rapax, certainly do not seem to be generically distinct from A. chrysaetos. Problem taxa. There has been much argument as to whether the nipalensis (with its weakly differentiated subspecies orientalis) is conspecific with the , rapax of Africa and . Stresemann (ms, see Stresemann & Amadon 1979, 272) had nipalensis as a species and Brooke et al. (1972) are very strongly of that opinion. The late. L. H. Brown, on the other hand, presented the opposite point of view with equal emphasis (in litt.). I now consider nipalensis a species in part because it is a long distance migrant while rapax is sedentary and in part because one might have expected the two to meet and intergrade someplace in if they are conspecific, though to be sure the configuration of and poses some difficulties in this regard. Aquila pomarina and hastata The of western Eurasia has an isolated representative in India, by name hastata, which recently is usually regarded as conspecific with it. Glutz et al. (1971) state that the two differ chiefly in certain features of the immature plumage. Stresemann (Stresemann & Amadon 1979: 273) called hastata a full species but based on present information, I see no reason to do so, although as with rapax and nipalensis, one of the two, nominate pomarina, is migratory, the other sedentary. Aquila heliaca. It has been suggested that the Spanish-Moroccan race of the Imperial Eagle, adelberti, is specifically distinct from the nominate form of heliaca which presently occurs no closer than Greece and the Balkans; though this gap is probably the result of recent human . The characters separating the two hardly seem to require such action. Species. 1-wahlbergi, 2-pomarina, 3-, 4-nipalensis, 5-rapax, 6-heliaca, 7- gurneyi, 8-chrysaetos, 9-audax, 10-verreauxii. As noted above, nipalensis is often regarded as a subspecies of rapax; if not, they form a superspecies. Aquila pomarina and clanga may form a superspecies though at present they overlap to some extent in breeding range.

Genus Hieraaetus

Hieraaetus Kaup, 1844, Class. Saugeth. u. Vog.: p. 120. Type: Falco pennata Gmelin. Entolmaetus Blyth, 1845, Jour. Asiatic Soc. Bengal, 14: 174. Type: Aquila fasciata Vieillot. Polemaetus Heine, 1890, in Heine and Reichenow, Nomencl. Mus. Heineani Orn., p. 270. Type: Falco bellicosus Daudin. Anomalaetus Roberts, 1922, Ann. Transvaal Mus., 8: 208. Type: Spizaetus ayresii Gurney. 114 D. Amadon

Diagnosis. As compared with Aquila: form more slender; size usually smaller; tail relative to wings averaging a little longer, about .55 to .60. Tail nearly square or slightly emarginate. Bill shorter, relatively broader, culmen curved for its full length; nares elliptical. Color pattern usually more varied, never prevailingly black or brown (except in dark phase pennatus); flight quills usually somewhat barred. Sometimes with a wedge- shaped occipital crest. Immatures usually unlike adult: immaculate white or buff below, but sometimes darker than adult, as in certain H. morphnoides (Cupper and Cupper 1981). Size of talons and relative length of toes variable, but talons formidable in fasciatus and bellicosus. Sexual dimorphism in size greater. As compared with Spizaetus: wings longer, tail shorter; color pattern less varied and with less barring; usually crestless; never with a long occipital crest of three or four narrow feathers. Indentations on inner vanes of outer primaries deeper than in either Aquila or Spizaetus. Remarks. These active, dashing eagles secure their food, which usually includes many birds, by swift stoops into the treetops or to the ground. Even the large (bellicosus) seeks birds such as (Numididae), which it sometimes seizes after very long stoops; but it is capable of taking young antelope. The Australian (H. morphnoides), despite its similarity to the genotype, H. pennatus, may be more sluggish than the other members of its genus, though this aspect is probably overem- phasized in the account in Brown and Amadon (1968). Birds from the size of pipits to quail figured significantly in the diet of nesting pairs, along with the introduced rabbit which has become a staple in many areas (Cupper & Cupper 1981). The Russian Handbook (1966, Dement'ev et al.) treats Hieraaetus as a of Aquila but I think that Glutz et al. (1971) were correct in saying that it is closer to Spizaetus even though as noted above Aquila wahlbergi is somewhat intermediate towards Hieraaetus. The species of Hieraaetus almost never take carrion. They build large stick nests in trees; only one (fasciatus) sometimes nesting on cliffs. In some of the species clutch size is only one egg. The superb Martial Eagle, described as Falco bellicosus received its own generic name Polemaetus in 1890 and has since been left in this monotypic genus. Nevertheless it seems to be only a very large offshoot of Hieraaetus adapted for life in more open country than the members of Hieraaetus, except perhaps the Australian Little Eagle. I am merging the two genera. Like several species of Hieraaetus, bellicosus hunts chiefly while on the wing, and often at a great height; indeed its home range must be equalled by that of very few other land birds. Immature Martial Eagles are off-white below and on the head and quite similar to the young of "Stephanoaetus" coronatus, but the proportions are very different: Hieraaetus (Polemaetus) bellicocus has relatively much longer wings and shorter tail; indeed the tail in this species is only about one half the wing in length and hence relatively short even for Hieraaetus. Impressive though the tarsi and talons of bellicosus are, they do not equal those of coronatus in the sheer size of these weapons. Species' nomenclature. Ayre's Hawk-eagle was described as Spizaetus ayresii; this species name was still in use in Peters Check-List (1931). Five years later Roberts (1936) stated that Morphinus dubius is an earlier name for this eagle and this was rather Genera of Booted Eagles 115 uncritically accepted. Recently Brooke and Vernon (1981) have shown rather convinc- ingly that dubius was based on a specimen of H. pennatus, which in the past few years has been shown to breed in , which it also reaches occasionally as a migrant. Hence they urge us to go back to the name ayresii. Although disliking changes of name, ayresii is in all respects the more suitable one, and probably I am not the only individual who has had difficulty in remembering that we were not to use it. Therefore, Hieraaetus ayresii let it be! Problem taxa. The Russian Handbook (Dement'ev et al. 1966) treats Hieraaetus pennatus, morphnoides, and ayresii as conspecific although the very different, as regards adult plumage and presence of a crest, H. kienerii, separates the first two of these three by a gap of 1500 km or more. Further, pennatus, as noted above, breeds in South Africa as well as in Eurasia, thus on both sides of the range of ayresii, and without interacting with it in . Thus it would seem that the three species are not quite as closely related as would appear at first glance; their habits seem to vary to some extent interspecifically as well. They are almost certainly not conspecific; perhaps they comprise a superspecies and if so kienerii may belong to it, despite its long toes and claws, probably adapted for catching birds, and its different color. Hieraaetus spilogaster and fasciatus. These two hawk-eagles have been called conspecific since the time of Hartert, but recently writers (e.g. Glutz et al. 1971) have pointed out distinctions in the color of the chicks, of the flight shafts, etc. and have reverted to the old view that they are species. This may be accepted as probable but of course not proven. Hieraaetus morphnoides and weiskei. The poorly known New Guinea repre- sentative of the Australian Little Eagle, weiskei, is so much smaller than the Australian morphnoides that Stresemann (ms, see Stresemann & Amadon 1979: 273) listed it as a species. Most would think it falls within usual limits for subspecies. Species. 1-pennatus, 2-morphnoides, 3-ayresii (dubius, auct.), 4-kienerii, 5-spilo- gaster, 6-fasciatus, 7-bellicosus. Spilogaster and fasciatus form a superspecies (if not conspecific). Pennatus, morphnoides, ayresii, and possibly kienerii may form another.

Genus Spizastur

Diagnosis. Very similar to Hieraaetus but mandibular rami (sides of lower beak) unfeathered (Fig. 1); notches on inner vanes of longer primaries perhaps a little shallower. Color pattern different: adult and immature very similar-unmarked white below and on head except for a short, black crest of wedge-shaped feathers. Hence the adult is much like the immature of some species of Hieraaetus, notably kienerii (Figs. 1 and 2). Tail perhaps averaging a little longer in relation to wing than in Hieraaetus: about .67. Talons long and powerful, but relatively no more so than in H. fasciatus. Remarks. Earlier (Amadon 1964) I noted the great similarity of Spizastur to Hieraaetus but refrained from combining them not so much because of the trifling distinctions listed above but because Spizastur is the older name, even though its single, neotropical species is much less well known than Hieraaetus fasciatus and H. pennatus 116 D. Amadon

Fig. 1. Left, Spizastur melanoleucus; right , Hieraaetus kienerii, immature.

Fig. 2. Left, Spizastur melanoleucus , center; Hieraaetus kienerii, immature; right, Hieraaetus kienerii, adult. Genera of Booted Eagles 117 and the other species of Hieraaetus. Furthermore in combining genera from different hemispheres one must be a little more careful than would otherwise be the case. As regards Spizastur melanoleucus the question is whether it might be an atypical offshoot of the American stock of Spizaetus rather than a representative of the otherwise Old World genus Hieraaetus. My own brief sighting of the Black and White Hawk-eagle as it is called (Amadon & Eckelberry 1955) was rather inconclusive: it looked very buteonine when soaring; perched it was erect, flat crowned and aquiline; it was immediately harrassed by a small group of Brown Jays (Psilorhinus). Dr. K. H. Voous, who has seen the species in Suriname, suggests to me that its habits may be somewhat different from typical Hieraaetus: less dashing and presumably pouncing on its prey from a perch as do the species of Spizaetus. If it is an offshoot of the latter genus, it could be compared in some respects with S. africanus. All in all it seems best to postpone a decision as to whether Spizastur should be combined with either Hieraaetus or Spizaetus. It again illustrates the difficulty of separating these two genera. Species. 1-melanoleucus.

Genus Spizaetus

Spizaetus Vieillot, 1816, Analyze, p. 24. Type: Falco ornatus Daudin. Ptenura Kaup, 1847, Bull. Mus. Senkenberg., 3: 259. Type: Falco tyrannus Wield. Lophaetus Kaup, 1847. Isis, column 165. Type: Falco occipitalis Daudin. Oroaetus Ridgway, 1920, Smiths. Misc. Colls., 72 (4): 1. Type: Falco isidori Des Murs. Phoeoaetus Ridgway, 1920, Smiths. Misc. Coils., 72 (4): 2. New name for Limnaetus Horsfield, preoccupied. Type: Falco limnaetus Horsfield = Spizaetus (cirrhatus) limnaeetus. Stephanoaetus W. L. Sciater, 1922, Bull. British Orn. Club, 42: 75. Type: Falco coronatus Linnaeus. Cassinaetus W. L. Sclater, 1922, Bull. British Orn. Club, 42: 76. Type: Limnaetus africanus Cassin. Limnaetops Baker, 1930, Fauna Brit. India, ed. 2, Bds., 7: p. 408. Type: Falco cirrhatus Gmelin.

Diagnosis. As compared with Hieraaetus: tail relatively longer, rounded; wings relatively shorter, more rounded; inner vanes of longer primaries less deeply incised. Usually with a long occipital crest composed of three to five feathers. Plumage, including wing and tail quills, usually more variegated, barred, and streaked. Toes relatively short; talons long and well curved, varying considerably in heaviness. Nares round. Remarks. The hawk-eagles of the genus Spizaetus are typically birds of the interior of forest. Some of them venture into more open country or drier ; tyrannus, for example, often soars over semi-open country and has been found nesting there, while S. cirrhatus of India, a typical member of the genus in proportions, is by no means limited to forest. In general the species of Spizaetus pounce on their prey from a perch rather than hunting it in flight or by pursuing birds in the air. Some species, such as S. ornatus the type of the genus, have prolonged aerial displays in which they fly high above the forest, and it is quite possible that such species strike down some of their prey in the trees and perhaps catch slow-flying birds in flight. In fact, ornatus is known to catch curassows (Crax), birds that weigh more than it does, as they perch or fly among trees. Hence the contrast between the hunting methods of species of Spizaetus and 118 D. Amadon

Hieraaetus and the associated proportions of wing and tail are by no means absolute. Spizaetus has always been rather difficult to separate from Hieraaetus. For example, Spizaetus (cirrhatus) limnaeetus lacks a crest and has a black phase in which the barring characteristic of this genus is lacking. Spizaetus africanus is aberrantly colored: almost immaculate white below in the adult, with immature more heavily marked, and has been placed in Hieraaetus or even in a genus of its own Cassinaetus. Nontheless, as shown by Stresemann (1924) and confirmed by Voous and Wijsman (1964) in proportions and it belongs to Spizaetus. Its tail/wing ratio of about .67 is a little less than in S. ornatus in which it is about .70-.75 but this character too is quite variable. In S. tyrannus, surely a close relative of the genotype S. ornatus, this ratio is about.80. Generic synonyms. The Ornate Hawk-eagle, S. ornatus, of the American tropics, is the genotype of Spizaetus. Later Horsfield applied a genus name Limnaetus to the taxon now usually known as S. cirrhatus limnaeetus, the "Changeable" Hawk-eagle. This was preoccupied and Ridgway renamed it Phoeoaetus. Still later Stuart Baker supplied a genus name Limnaetops for nominate cirrhatus itself! but the resemblance between cirrhatus-limnaeetus on the one hand, and ornatus on the other, even though they are native to different hemispheres, is sufficiently great that no recent author has sought to separate them generically. As will be evident from the synonymy given above, three monotypic genera, Lophaetus, Oroaetus and Stephanoaetus, are here combined with Spizaetus, none for the first time. Stephanoaetus represents the least debatable of these changes for it is only a very large Spizaetus with enormously heavy feet and talons; the name Stephanoaetus was based solely upon this. However there was already considerable variation in this character, e.g., S. tyrannus is comparatively long legged and light footed. On the other hand, S. africanus, though quite small, is heavy footed. In coloration, display, and other features, the African Crowned Eagle is a typical Spizaetus and as Voous and Wijsman (1964) among others have said, may well be accomodated in that genus. Its indented crest is unusual, curiously the Harpy Eagle (Harpia) has a similar one. In actual wing length S. coronatus is scarcely larger than the Japanese Hawk-eagle, S. nipalensis orientalis. The African Long-crested Eagle is another aberrant member of the genus Spizaetus if one chooses to place it there. In most recent works it occupies a monotypic genus Lophaetus (not Lophoaetus as misspelled in Brown & Amadon 1968) described by Kaup as long ago as 1847. The species name occipitalis refers to the very long crest. This is a buteonine Spizaetus with uncharacteristically short tail and long legs. Its food is almost entirely rodents which is pounces upon in grass, hence the long tarsi. It prefers mixed woodland and glades. Its black coloration and the similarity of young and adult are also unusual in Spizaetus but rivaled by S. tyrannus and the black phase of S. cirrhatus limnaeetus. Its proportions and coloration recall some of the smaller species of Aquila such as A. pomarina and I note that Brooke et al. (1972) believed these two species to be related. But the crest of occipitalis is entirely wrong for Aquila and the late L. H. Brown assured me that its true affinities lie with Spizaetus. Dr. Stresemann was obviously of the same opinion, for as noted above he actually placed Lophaetus in Spizaetus, despite his Genera of Booted Eagles 119 reluctance to merge genera. The Black and Chestnut Eagle, "Oroaetus" isidori, is a large, robustly built, and heavily taloned species of the forested slopes of the Andes . Its closest relative may well be the Ornate Hawk-eagle, Spizaetus ornatus, of the tropical at the foot of the mountains, which has some chestnut in its plumage. The immature plumage of the two is so similar as to cause that of isidori to be described as a different species, Spizaetus "devillei" and recognized as such even in Peters Check -List of Birds of the World (1931). I (1950) later published a photograph showing the transitional stages to the very different adult plumage. Isidori and ornatus have similar occipital crests. A close comparison of isidori and ornatus at any stage will show the former to be a larger, stockier more heavily taloned species. Ridgway (1920) in describing Oroaetus also called attention to its unusually broad tail feathers; the relatively short almost square tail and long wings, the better developed "flags" (lengthened feathers) on the thighs and the unusual coloration. Lehmann (1959) who learned most of what little is known of its habits, found isidori to range widely above the rugged slopes and valleys of its montane habitat: probably this is why it has evolved relatively long wings and short tail. It often stoops on its prey-squirrels and other arboreal mammals-in the treetops rather than dropping from a perch to pounce on them on the ground like a typical Spizaetus but catches domestic fowl and doubtless other prey on the ground. Thus it has diverged in the direction of Hieraaetus in habits and its proportions reflect this, but its true affinities seem to lie with Spizaetus, and I think it best to place it back in that genus. Problem taxa. Spizaetus(cirrhatus) limnaeetus as already noted, differs from nominate S. cirrhatus of India by having a dark phase and by lacking a crest. Limnaeetus and nominate cirrhatus may meet somewhere in the eastern foothills of the , but if so no one, to my knowledge, has studied them in that area. It may be noted that S. cirrhatus andamanensis, of the islands after which it is named, is intermediate between nominate cirrhatus and limnaeetus in that its crest is short; nontheless, limnaeetus may eventually be shown to be a full species. Stresemann (1924) briefly described an eagle from the island of Java as Spizaetus nipalensis bartelsi. It has also been listed as Spizaetus nanus bartelsi. Through the kindness of Dr. G. F. Mees I have recently been able to examine the fine series of bartelsi, including the type specimen, housed in the Leiden Museum. Bartelsi is similar in coloration of immature and of adult to both nipalenis and nanus; in size and proportions it is, of course, more like nipalensis than the diminutive nanus. If bartelsi lived adjacent to nipalensis there would be no hestiation in calling it a subspecies of that form, but the very different S. alboniger, with its sharply black and white adult plumage, occurs in the intervening area, from southern south over Sumatra and Borneo. The range of alboniger is almost exactly that of S. nanus. Thus in this area and nowhere else we have three more or less typical species of the genus Spizaetus: alboniger, nanus, and limnaeetus. May it not be, then, that the distinctive adult plumage of alboniger has evolved as a species recognition mark? The loss of a crest in limnaeetus might be viewed in the same light, but why the black color phase of this, the "Changeable" Hawk -eagle should add anything but confusion to species recognition is 120 D. Amadon more difficult to see. Viewed thus, Spizaetus bartelsi may be considered one of a chain of species representing S. nipalensis on various islands. The other members of this superspecies are alboniger, lanceolatus (Sulawesi), and philippensis (Philippine Islands). If this is correct the fact that bartelsi is most like nipalensis in color and pattern has no particular significance. This interpretation may be an oversimplification; it does not suggest how nanus evolved. In passing, it may be noted that S. nipalensis orientalis of Japan has almost lost the crest (as for that matter has lanceolatus); this isolated form may also be on the way to species status. It may be noted that all of the Asiatic species of Spizaetus are quite similar and typical (except for loss of crest in some of them, and black phase of S. cirrhatus limnaeetus); that two of the three neotropical species ornatus and tyrannus fit the same mold, but the third, isidori is aberrant, while all three of the African species are to some degree atypical, coronatus and occipitalis more so than africanus, but at the same time very unlike each other. Species. 1-africanus, 2-cirrhatus, 3-nipalensis, 4-alboniger, 5-bartelsi, 6-lanceolatus, 7 philippensis, 8-nanus, 9-coronatus, 10-ornatus, 11-tyrannus, 12-isidori.

References

Amadon, D. 1953. Remarks on the Asiatic Hawk-eagles of the genus Spizaetus. 95: 492-500. Amadon, D. 1950. What is Spizaetus devillei Dubois? Auk 67: 235-236. Amadon, D. 1964. Taxonomic notes on birds of prey. Amer. Mus. Novitates 2166: 24 pp. Amadon, D. 1982. A review of the sub-buteonine hawks. Amer. Mus. Novitates, 2741: 20 pp. Amadon, D. & Eckelberry, D. R. 1955. Observations on Mexican birds. Condor 57: 65-80. Brodkorb, P. 1964. Catalogue of Fossil Birds, pt. 2. Bull. Florida State Mus. 8: 195-335. Brooke, R. K. 1974. On the material evidence of Hieraetus pennatus in southern Africa. Bull. British Orn. Cl. 94: 151-158. Brooke, R. K. 1981. Early records of two small Hieraaetus eagles (Aves: Accipitridae) in the Cape Province of South Africa. Ann. Cape Prov. Mus. 13: 133-137. Brooke, R. K., Grobler, J. H., Irwin, M. P. S. & Steyn, P. 1972. A study of the migratory eagles Aquila nipalensis and A. pomarina (Aves: Accipitridae) in southern Africa, with comparative notes on other large raptors. Occ. Papers Nat. Mus. Rhodesia B5: 61-114. Brooke, R. K. & Vernon, C. J. 1981. Early names and records of two small Hieraaetus eagles (Aves: Accipitridae) in the Cape Province of South Africa. Ann. Cape Prov. Mus. (nat. hist.) 13: 133-137. Brown, L. H. & Amadon, D. 1968. Eagles, Hawks, and Falcons of the World. McGraw-Hill, New York; Hamlyn, England. Cupper, J. & Cupper, L. 1981. Hawks in Focus. Jacklin, Mildura, Australia. Dement'ev, G. P. & Gladkov, N. A. (eds.). 1966. Birds of the Soviet Union, I. Smithsonian, Washington (trans. of 1951 Russian work.) Glutz von Blotzheim, U. N., Bauer, K. M. & Bezzel, E. (eds.). 1971. Handbuch Vogel Mitteleuropas, 4. Akademische Verlag, Frankfurt. Hartert, E. 1903-1923. Vogel palearctischen Fauna. Friedlander, Berlin. Howard, H. 1948. An ancestral raises a question in . Auk 64: 287-291. Jollie, M. P. 1957. Comments on Aquila gurneyi. Nova Guinea 8: 179-181. Lehman, F. C. 1959. Nuevas observaciones sobre Oroaetus isidori (Des Murs). Novedades Colombianas,1: 168-195. Peters, J. L. 1931. Check-List of Birds of the World. I. Harvard, Cambridge. Genera of Booted Eagles 121

Rand, A. L. & Gilliard, E. T. 1967. Handbook of New Guinea Birds. Weidenfeld and Nicholson, London. Roberts, A. 1936. Some unpublished field notes made by Dr. (Sir) Andrew Smith. Ann. Transvaal Mus. 18: 271-323. Stresemann, E. 1924. Uber Hieraaetus ayresii and Spizaetus africanus. Novit. Zool. 31: 214-216. Stresemann, E. & Amadon, D. 1979. Falconiformes, in, Check-List Birds of the World. I. (rev. ed.). Mayr, E. & Cottrell, G. W. eds.). Cambridge: Harvard Univ. Suschkin, P. 1899. Beitrage zur Classification der Tagraubvogeln. Zool. Anzeiger: 1-18. Suschkin, P. 1905. Vergleichende Osteologie der Accipitres. Mem. Soc. Nat. Moscou: 1-247. Voous, K. H. & Wijsman, H. J. W. 1964. Notes on African Hawk-eagles. Biol. Jaar.: Dodonaea, Ghent, 32: 151-163.