The Aquilinae are a subfamily of of the family Accipitridae. The general common name used for members of this subfamily is " booted eagle", although this is also the Booted eagle of a member of the subfamily,[Lerner, H., Christidis, L., Gamauf, A., Griffiths, C., Haring, E., Huddleston, C. J., Kabra, S., Kocum, A., Krosby, M., Kvaloy, K., Mindell, D., Rasmussen, P., Rov, N., Wadleigh, R., Michael Wink & Gjershaug, J. O. (2017). Phylogeny and new taxonomy of the Booted Eagles (Accipitriformes: Aquilinae). Zootaxa 4216 (4), 301-320.] or " true eagle", though this term can more narrowly be applied to the genus Aquila. At one point, this subfamily was considered inclusive with the Buteoninae (commonly known as buzzards or buteonine hawks) based probably on some shared morphological characteristics.[Amadon, D. (1982). The genera of booted eagles: Aquila and relatives. Journal of the Yamashina Institute for Ornithology, 14(2-3), 108-121.] However, research on the DNA of the booted eagles has shown that they are a Monophyly that probably have had millions of years of separation from other extant forms of accipitrid.[Lerner, H. R., Klaver, M. C., & Mindell, D. P. (2008). Molecular phylogenetics of the Buteonine birds of prey (Accipitridae). The Auk, 125(2), 304-315.][Lerner, H. R., & Mindell, D. P. (2005). Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA. Molecular Phylogenetics and Evolution, 37(2), 327-346.]
Description
The Aquilinae consists of medium-sized to very large species. Modern species range in mass from the recently recognized pygmy eagle ( Hieraaetus weiskei) of Papua New Guinea, which weighs about , to the martial eagle ( Polemaetus bellicosus) and golden eagle ( Aquila chrysaetos), which both weigh about on average.[del Hoyo, J., Collar, N. & Marks, J.S. (2017). Pygmy Eagle (Hieraaetus weiskei). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona.][Mendelsohn, J.M., Kemp, A.C., Biggs, H.C., Biggs, R., & Brown, C.J. (1989). Wing areas, wing loadings and wing spans of 66 species of African raptors. Ostrich, 60(1), 35-42.] The record sizes for wild booted eagles are for a golden eagle in body mass and for a wedge-tailed eagle in wingspan.[Worthy, T. & Holdaway, R., The Lost World of the Moa: Prehistoric Life of New Zealand. Indiana University Press (2003), ][Ferguson-Lees & Christie, Raptors of the World. Houghton Mifflin Company (2001), .] Many species within the subfamily are colored for camouflage with varying patterns of brown, black, yellowish or white being commonplace, darker colors being favored by forest dwelling varieties and brown to straw coloring common to open country species. A few more brightly colored species (in adult plumage), with striking patterns of chestnut in about four, none more striking than the ornate hawk-eagle ( Spizaetus ornatus).[ Roughly half of booted eagle species have a strikingly different looking juvenile plumage, which can in some species be nearly all white, but even where the differences are subtle between adults and immatures, usually some physical differences are noticeable such as white wing patches in traditional Aquila species, to visually distinguish young from adults.][ Many species have a notable head-crest, such as Nisaetus and most Spizaetus, with the feature being most extreme in the long-crested eagle ( Lophaetus occipitalis).][ Like most accipitrids, they have large powerful hooked for tearing flesh from their prey, strong legs and powerful talons. Compared to other large raptors, the feet and talons of booted eagle species are often particularly large and powerful relative to their size. The most extreme example seems to be the crowned eagle, which has a hallux-claw (or rear talon) of around about the same sized hallux-claw as the Philippine eagle ( Pithecophaga jefferyi) (not part of the Aquilinae), which weighs on average nearly twice as much.][Prout-Jones, D. V., & Kemp, A. G. (1997). Moult, plumage sequence and maintenance behaviour of a captive male and female crowned eagle, Stephanoaetus coronatus (Aves: Accipitridae). Annals of the Transvaal Museum, 36(Part 19).]
Life histories and range
Booted eagles are varying in their habitats and habits, being found on every continent inhabited by accipitrids, which includes all continents with the exception of Antarctica. They may inhabit nearly all of the world's terrestrial habitats, with the majority of species being largely forest dwelling, but several preferring all kinds of open habitat from steppe to prairie to tundra as well as most rocky or mountainous areas. By far the widest ranging species of booted eagle is the golden eagle, which is distributed in most of North America (where it is the only species of the subfamily north of Mexico) and much of Eurasia including a majority of Europe, often along most mountainous terrains therein but also other land-based habitats with typically remote semi-open or hilly hunting grounds accessible.[Haring, E., Kvaløy, K., Gjershaug, J. O., Røv, N., & Gamauf, A. (2007). Convergent evolution and paraphyly of the hawk-eagles of the genus Spizaetus (Aves, Accipitridae)–phylogenetic analyses based on mitochondrial markers. Journal of Zoological Systematics and Evolutionary Research, 45(4), 353-365.] The peak diversity for Aquilinae are in Africa, where nearly half of extant species are known to dwell at least seasonally, exploiting a diversity of different hunting styles, habitats, nesting habits and general body forms.[ All booted eagle species are opportunistic predators which prey mostly on small , often subsisting on a wide range of , , and as they become locally available or abundant (carrion is also rarely ignored). Species favoring more open habitats tend to hunt most often on the wing, using distance or hugging contours of the ground to surprise prey. Forest dwelling species are more likely to be perch-hunters, watching for prey activity from a high tree perch, but every kind of booted eagle can vary their hunting techniques when necessary.][ In cases where they become specialists, booted eagles tend to be mammal hunters, such as the considerable dependence of Spanish imperial eagle ( Aquila adalberti) on European rabbit, of breeding steppe eagle ( Aquila nipalensis) on Spermophilus or Verreaux's eagle ( Aquila verreauxii) on .][González, L. M. (1996). Action plan for the Spanish imperial eagle (Aquila adalberti). Globally Threatened Birds in Europe: Action Plans (Council of Europe and BirdLife International Strasbourg 1996), 175-189.][Birazana, O., & Damdin, S. (2012). BREEDING ECOLOGY OF THE STEPPE EAGLE (Aquila nipalensis) IN MONGOLIA Gombobaatar Sundev, Reuven Yosef1. Ornis Mongolica, 13.][Dewhurst, C. E., & van Someren, C. (1988). Observation on the breeding ecology of Ayres' hawk eagle Hieraaetus ayresii at Karen, Nairobi, Kenya. Gabar., 3(2), 85-93.] Most booted eagle species have relatively large feet and talons and can semi-regularly go after prey as large or larger than themselves, even smaller species can occasionally dispatch prey of up to two to three times their own weight.[Calaby, J. H. (1951). Notes on the little eagle; with particular reference to rabbit predation. Emu - Austral Ornithology, 51(1), 33-56.][Smeenk, C. (1974). Comparative-ecological studies of some East African birds of prey. Ardea 62 (1-2) : 1-97.] Rare attacks on large prey, such as , adult or medium-sized Carnivora or other much larger animals, usually involve the larger species of booted eagle, whereas such attacks are exceptionally rare to non-existent in eagles of other lineages. At least four large booted eagles have been known to dispatch prey weighing or more.[Steyn, P. (1983). Birds of prey of southern Africa: Their identification and life histories. Croom Helm, Beckenham (UK). 1983.][Olsen, P. (2005). The Wedge-tailed Eagle. CSIRO Publishing (Australian Natural History Series), .][Nybakk, K., Kjelvik, O. & Kvam, T. 1999. Golden Eagle predation on semidomestic reindeer. Wildlife Society Bulletin, 27 (4): 1038-1042.][Phillips, R.L., Cummings, J.L., Notah, G. & Mullis, C. 1996. Golden eagle predation on domestic calves. Wildlife Society Bulletin, 24: 468-470.]
Booted eagles, like almost all raptorial birds, are strongly territorial and tend to maintain expansive home ranges against conspecifics.[Janes, S. W. (1985). Habitat selection in raptorial birds. Habitat selection in birds. Academic Press, New York, 159-188.] Given their need for ample hunting ranges, the territory of most booted eagles tend to be extremely large, with several dozen square kilometers being common.[Bosch, R., Real, J., Tinto, A., Zozaya, E. L., & Castell, C. (2010). Home-ranges and patterns of spatial use in territorial Bonelli's Eagles Aquila fasciata. Ibis, 152(1), 105-117.][Bergo, G. (1987). Territorial behaviour of Golden Eagles in western Norway. British Birds, 80, 361-376.] Territories are usually maintained with display flights but vocal displays are known in some of the denser forest dwelling varieties.[Brown, L., & Amadon, D. (1968). Eagles, hawks and falcons of the world (Vol. 2, p. 445). London: Country Life Books.] Nests of Aquilinae tend to be typically large as in most , with ample surface space needed, whether located in trees, rocky formations or on the ground.[ As is typical in many raptorial birds, pair bonds are strong between males and females and in many booted eagle species, they may mate for life. Primarily females incubate the egg and brood the young, while males usually have the responsibility of food capture.][ Clutch sizes are usually small in booted eagles, rarely more than 3 eggs are laid, and most parents will manage to produce only one to two fledglings depending on species. In most booted eagles, beyond threats from the outside world, most eggs are laid and hatched at intervals, thus one sibling is usually considerably bigger and often Siblicide its younger siblings.][Simmons, R. (1988). Offspring quality and the evolution of cainism. Ibis 130 (3): 339–357.] While brood size and fledgling rates are typically low, booted eagles may have even lower productivity due to the long dependence period of the young relying on their parents for food and protection, and some species may only nest every other year.[Brown, L. 1976. Eagles of the World. David and Charles, .]
General status
Due to their large territories and low productivity, most booted eagle species are sparsely distributed and not infrequently uncommon-to-rare even in regional strongholds where ample habitat remains. Booted eagle species tend to be highly sensitive to human activities, mainly habitat alteration or destruction, human disturbance, collision with man made objects (especially non-insulated electrical pylons and wind turbines), accidental or intentional killing of staple prey species and various forms of persecution by humans. Due mainly to these factors, seven species of booted eagle are currently classified as Vulnerable to extinction by the IUCN. Four little-known forest dwelling species are classified in more severe status as Endangered: the Philippine hawk-eagle ( Nisaetus philippensis), Pinsker's hawk-eagle ( Nisaetus pinskeri), Javan hawk-eagle ( Nisaetus bartelsi) and the black-and-chestnut eagle ( Spizaetus isidori). A very different eagle, the steppe eagle, is also considered Endangered despite having been considered one of the most numerous of all eagles after a disastrous, ongoing decline mostly due to from dangerous powerlines, poisonings and increasing wildfire around nests, these killing them off en masse while breeding and migrating. An even more drastic classification of Critically Endangered was given to the Flores hawk-eagle ( N. floris). In all five endangered hawk-eagles, near epidemic levels of forest habitat degradation, primarily direct deforestation, has been determined as the primary cause of their declines.[Collaerts, P., Collaerts, E., Verbelen, P., & Trainor, C. R. (2011). Discovery of the Critically Endangered Flores Hawk Eagle Nisaetus floris on Alor island, Indonesia. BirdingASIA 19 (2013): 48–51.][Tingay, R. E., & Katzner, T. E. (Eds.). (2010). The eagle watchers: Observing and conserving raptors around the world. Cornell University Press.][Meyburg, B. U. (1986). Threatened and near-threatened diurnal birds of prey of the world. Birds of Prey Bull, 3(1), 12.]
Systematics
The cladogram of the Aquilinae shown below is based on a molecular phylogenetic study of the Accipitridae by Therese Catanach and collaborators that was published in 2024.
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N. kelaarti- Legge's hawk-eagle
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N. nanus- Wallace's hawk-eagle
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N. nipalensis- Mountain hawk-eagle
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N. alboniger- Blyth's hawk-eagle
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N. bartelsi- Javan hawk-eagle
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N. lanceolatus- Sulawesi hawk-eagle
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N. pinskeri- Pinsker's hawk-eagle
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N. philippensis- Philippine hawk-eagle
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N. cirrhatus- Changeable hawk-eagle
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N. floris- Flores hawk-eagle
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| | Spizaetus |
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S. tyrannus- Black hawk-eagle
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S. melanoleucus- Black-and-white hawk-eagle
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S. ornatus- Ornate hawk-eagle
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S. isidori- Black-and-chestnut eagle
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L. kienerii- Rufous-bellied eagle
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L. occipitalis- Long-crested eagle
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C. hastata- Indian spotted eagle
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C. pomarina- Lesser spotted eagle
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C. clanga- Greater spotted eagle
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| | Hieraaetus | |
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A. nipalensis- Steppe eagle
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A. rapax- Tawny eagle
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A. adalberti- Spanish imperial eagle
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A. heliaca- Eastern imperial eagle
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A. chrysaetos- Golden eagle
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A. africana- Cassin's hawk-eagle
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A. audax- Wedge-tailed eagle
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A. gurneyi- Gurney's eagle
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A. verreauxii- Verreaux's eagle
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A. fasciata- Bonelli's eagle
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A. spilogaster- African hawk-eagle
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