| Aquilinae | |
|---|---|
%2c_at_Ndumo_Nature_Reserve%2c_KwaZulu-Natal%2c_South_Africa_(28842574882).jpg) | |
| Crowned eagle (Stephanoaetus coronatus) inSouth Africa. | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Accipitriformes |
| Family: | Accipitridae |
| Subfamily: | Aquilinae |
| Genera | |
About 10, see article | |
TheAquilinae are a subfamily ofeagles of the familyAccipitridae. The general common name used for members of this subfamily is "booted eagle", although this is also thecommon name of a member of the subfamily.[1] At one point, this subfamily was considered inclusive with theButeoninae (commonly known as buzzards or buteonine hawks) based probably on some shared morphological characteristics.[2] However, research on theDNA of the booted eagles has shown that they are amonophyletic group that probably have had millions of years of separation from other extant forms of accipitrid.[1][3][4]
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The Aquilinae consists of medium-sized to very largespecies. Modern species range in mass from the recently recognizedpygmy eagle (Hieraaetus weiskei) ofPapua New Guinea, which weighs about 500 g (1.1 lb), to themartial eagle (Polemaetus bellicosus) andgolden eagle (Aquila chrysaetos), which both weigh about 4.2 kg (9.3 lb) on average.[5][6] In wingspan, extant Aquilinae range from the pygmy eagle, with a median of 1.18 m (3 ft 10 in), to thewedge-tailed eagle (Aquila audax) and martial eagles, which average about 2.15 m (7 ft 1 in) and 2.12 m (6 ft 11 in) in wingspan, respectively. Total length can vary from 38 to 106 cm (15 to 42 in), in the pygmy and wedge-tailed eagles, respectively.[5][7][8][9] The record sizes for wild booted eagles are 7.7 kg (17 lb) for a golden eagle in body mass and 2.84 m (9 ft 4 in) for a wedge-tailed eagle in wingspan.[8][10] Dwarfing these species, the booted eagle speciesHaast's eagle (Hieraaetus moorei) ofNew Zealand, was probably the most massive species ever known in the entire accipitrid family, with females averaging an estimated 10 to 14 kg (22 to 31 lb) and perhaps weighing up to 17 kg (37 lb) and measuring up to about 140 cm (55 in) long, while males weighed an estimated 9 to 12 kg (20 to 26 lb). The Haast's eagle went extinct by the 16th century when human colonizers killed off their primary prey, themoas.[11][12] Beyond their typically large size, Aquilinae species have few outward shared characteristics as they are a fairly diverse subfamily. Nonetheless, every species shares the feature of their legs being covered in feathers. Only two buteonine hawks share this feature beyond the Aquilinae, in a presumed case ofconvergent evolution.[1][13] 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 theornate hawk-eagle (Spizaetus ornatus).[13] 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 traditionalAquila species, to visually distinguish young from adults.[13] Many species have a notable head-crest, such asNisaetus and mostSpizaetus, with the feature being most extreme in thelong-crested eagle (Lophaetus occipitalis).[13] Like most accipitrids, they have large powerful hookedbeaks for tearing flesh from their prey, strong legs and powerfultalons. 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 thecrowned eagle, which has a hallux-claw (or rear talon) of around 56 mm (2.2 in) about the same sized hallux-claw as thePhilippine eagle (Pithecophaga jefferyi) (not part of the Aquilinae), which weighs on average nearly twice as much.[14][15] The booted eagles also have extremely keen eyesight to enable them to spot potentialprey from a distance.[16]
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Booted eagles are varying in their habitats and habits, being found on every continent inhabited by accipitrids, which includes all continents with the exception ofAntarctica. 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 fromsteppe toprairie totundra as well as most rocky or mountainous areas. By far the widest ranging species of booted eagle is thegolden eagle, which is distributed in most ofNorth America (where it is the only species of the subfamily north ofMexico) and much ofEurasia including a majority ofEurope, often along most mountainous terrains therein but also other land-based habitats with typically remote semi-open or hilly hunting grounds accessible.[17] So-called "hawk-eagles" are forest dwelling booted eagle types largely represented bySpizaetus (in theneotropics) andNisaetus (inAsia). Despite many similar features in the two main hawk-eagle genera, they apparently evolved separately for some time and are not closely related.[18] The peak diversity for Aquilinae are inAfrica, 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.[1][13] All booted eagle species are opportunistic predators which prey mostly on smallvertebrates, often subsisting on a wide range ofmammals,birds,reptiles andamphibians 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.[13][17] In cases where they become specialists, booted eagles tend to be mammal hunters, such as the considerable dependence ofSpanish imperial eagle (Aquila adalberti) onrabbits, of breedingsteppe eagle (Aquila nipalensis) onsousliks orVerreaux's eagle (Aquila verreauxii) onhyraxes.[19][20][21] Exceptions include theAyres's hawk-eagle (Hieraaetus ayresii) and, to a lesser extent, therufous-bellied eagle (Lophotriorchis kienerii), both of which are smallish, swift-flying bird-hunting specialists who dive (falcon-like) on woodland birds while theblack eagle (Ictinaetus malaiensis) feeds largely on the contents of birds' nests andsquirreldreys (the only hawk or owl specialized to do so).[13][22] 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.[13][23][24] Rare attacks on large prey, such asungulates, adultmonkeys or medium-sizedcarnivores 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 30 kg (66 lb) or more.[25][26][27][28]
Booted eagles, like almost all raptorial birds, are strongly territorial and tend to maintain expansive home ranges against conspecifics.[29] 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.[30][31] Territories are usually maintained with display flights but vocal displays are known in some of the denser forest dwelling varieties.[13][32] Nests of Aquilinae tend to be typically large as in mosteagles, with ample surface space needed, whether located in trees, rocky formations or on the ground.[13][32] 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.[13][32] 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 oftenkills its younger siblings.[33] 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.[34]
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 asVulnerable to extinction by theIUCN. Four little-known forest dwelling species are classified in more severe status asEndangered: thePhilippine hawk-eagle (Nisaetus philippensis),Pinsker's hawk-eagle (Nisaetus pinskeri),Javan hawk-eagle (Nisaetus bartelsi) and theblack-and-chestnut eagle (Spizaetus isidori). A very different eagle, thesteppe eagle, is also considered Endangered despite having been considered one of the most numerous of all eagles after a disastrous, ongoing decline mostly due toelectrocutions from dangerous powerlines, poisonings and increasingsteppe fires around nests, these killing them off en masse while breeding and migrating. An even more drastic classification ofCritically Endangered was given to theFlores hawk-eagle (N. floris). In all five endangered hawk-eagles, near epidemic levels offorest habitat degradation, primarily directdeforestation, has been determined as the primary cause of their declines.[35][36][37]
Thecladogram of the Aquilinae shown below is based on amolecular phylogenetic study of the Accipitridae by Therese Catanach and collaborators that was published in 2024.[38]
| Aquilinae |
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