Eagle

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Eagle is the common name for many large birds of prey of the family Accipitridae. Eagles belong to several groups of genera, not all of which are closely related. Most of the 60 species of eagle are from Eurasia and Africa.[1]Outside this area, just 14 species can be found—2 in North America, 9 in Central and South America, and 3 in Australia.

Eagles are large, powerfully built birds of prey, with heavy heads and beaks. Even the smallest eagles, such as the booted eagle (Aquila pennata), which is comparable in size to a common buzzard (Buteo buteo) or red-tailed hawk(B. jamaicensis), have relatively longer and more evenly broad wings, and more direct, faster flight – despite the reduced size of aerodynamic feathers. Most eagles are larger than any other raptors apart from some vultures. The smallest species of eagle is the South Nicobar serpent eagle (Spilornis klossi), at 450 g (0.99 lb) and 40 cm (16 in). The largest species are discussed below. Like all birds of prey, eagles have very large, hooked beaks for ripping flesh from their prey, strong, muscular legs, and powerful talons. The beak is typically heavier than that of most other birds of prey. Eagles’ eyes are extremely powerful. It is estimated that the martial eagle, whose eye is more than twice as long as a human eye, has a visual acuity 3.0 to 3.6 times that of humans. This acuity enables eagles to spot potential prey from a very long distance.[2] This keen eyesight is primarily attributed to their extremely large pupils which ensure minimal diffraction (scattering) of the incoming light. The female of all known species of eagles is larger than the male.[3][4]

Eagles normally build their nests, called eyries, in tall trees or on high cliffs. Many species lay two eggs, but the older, larger chick frequently kills its younger sibling once it has hatched. The dominant chick tends to be a female, as they are bigger than the male. The parents take no action to stop the killing.[5][6]

Due to the size and power of many eagle species, they are ranked at the top of the food chain as apex predators in the avian world. The type of prey varies by genus. The Haliaeetus and Ichthyophaga eagles prefer to capture fish, though the species in the former often capture various animals, especially other water birds, and are powerful kleptoparasites of other birds. The snake and serpent eagles of the genera CircaetusTerathopius, and Spilornis predominantly prey on the great diversity of snakes found in the tropics of Africa and Asia. The eagles of the genus Aquila are often the top birds of prey in open habitats, taking almost any medium-sized vertebrate they can catch. Where Aquila eagles are absent, other eagles, such as the buteonine black-chested buzzard-eagle of South America, may assume the position of top raptorial predator in open areas. Many other eagles, including the species-rich genus Spizaetus, live predominantly in woodlands and forest. These eagles often target various arboreal or ground-dwelling mammals and birds, which are often unsuspectingly ambushed in such dense, knotty environments. Hunting techniques differ among the species and genera, with some individual eagles having engaged in quite varied techniques based their environment and prey at any given time. Most eagles grab prey without landing and take flight with it, so the prey can be carried to a perch and torn apart.[7]

The bald eagle is noted for having flown with the heaviest load verified to be carried by any flying bird, since one eagle flew with a 6.8 kg (15 lb) mule deer fawn.[8] However, a few eagles may target prey considerably heavier than themselves; such prey is too heavy to fly with, thus it is either eaten at the site of the kill or taken in pieces back to a perch or nest. Golden and crowned eagles have killed ungulates weighing up to 30 kg (66 lb) and a martial eagle even killed a 37 kg (82 lb) duiker, 7–8 times heavier than the preying eagle.[7][9]Authors on birds David Allen SibleyPete Dunne, and Clay Sutton described the behavioral difference between hunting eagles and other birds of prey thus (in this case the bald and golden eagles as compared to other North American raptors):[10]

They have at least one singular characteristic. It has been observed that most birds of prey look back over their shoulders before striking prey (or shortly thereafter); predation is after all a two-edged sword. All hawks seem to have this habit, from the smallest kestrel to the largest Ferruginous – but not the Eagles.

Among the eagles are some of the largest birds of prey: only the condors and some of the Old World vultures are markedly larger. It is regularly debated which should be considered the largest species of eagle. They could be measured variously in total length, body mass, or wingspan. Different lifestyle needs among various eagles result in variable measurements from species to species. For example, many forest-dwelling eagles, including the very large harpy eagle, have relatively short wingspans, a feature necessary for being able to maneuver in quick, short bursts through densely forested habitats.[7] Eagles in the genus Aquila, though found almost strictly in open country, are superlative soarers, and have relatively long wings for their size.

Eagles are often informally divided into four groups.[note 1][18]

The snake eagles are placed in the subfamily Circaetinae. The fish eagles, booted eagles, and harpy eagles have traditionally been placed in the subfamily Buteoninae together with the buzzard-hawks (buteonine hawks) and harriers. Some authors may treat these groups as tribes of the Buteoninae; Lerner & Mindell[19] proposed separating the eagle groups into their own subfamilies of Accipitridae.

Fish eagles

Sea eagles or fish eagles take fish as a large part of their diets, either fresh or as carrion.

Proposed subfamily Haliaeetinae. Genera: HaliaeetusIchthyophaga.

Some authors include Gypohierax angolensis, the “vulturine fish eagle” (also called the palm-nut vulture) in this group.[18] However, genetic analyses indicate it is related to a grouping of NeophronGypaetusEutriorchis (Egyptian vulturebearded vulture (lammergeier), and Madagascan serpent eagle).[20]

The fish eagles have a close genetic relationship with Haliastur and Milvus; the whole group is only distantly related to the Buteo group.[20]

Booted eagles

Booted eagles or “true eagles”[18][21] have feathered tarsi (lower legs).

Tribe Aquililae or proposed subfamily Aquilinae. Genera: AquilaHieraaetusSpizaetusOroaetusSpizasturNisaetus;[20] IctinaetusLophoaetusPolemaetus; and Stephanoaetus.[18][21]

See comments under eagle species for changes to the composition of these genera.

Snake eagles

Snake or serpent eagles are, as the name suggests, adapted to hunting reptiles.

  • Subfamily Circaetinae. Genera: CircaetusSpilornisDryotriorchisTerathopius.[18]
  • Eutriorchis (subfamily Gypaetinae or Circaetinae).

Despite filling the niche of a snake eagle, genetic studies suggest that the Madagascan serpent eagle Eutriorchis is not related.[20]

Harpy eagles

Harpy eagles[18] or “giant forest eagles”[17] are large eagles that inhabit tropical forests. The group contains two to six species, depending on the author. Although these birds occupy similar niches, and have traditionally been grouped together, they are not all related: the solitary eagles are related to the black-hawks, and the Philippine eagle to the snake eagles.

  • Harpy eagles (proposed subfamily Harpiinae)
    • Harpia harpyjaharpy eagle ― Central and South America.
    • Morphnus guianensiscrested eagle ― Central and South America.
    • Harpyopsis novaeguineaePapuan eagle ― New Guinea.
  • Philippine eagle
  • Solitary eagles
    • Chaco eagle or crowned solitary eagle, Buteogallus (formerly Harpyhaliaetuscoronatus ― South America.
    • Solitary eagle or montane solitary eagle, Buteogallus (formerly Harpyhaliaetussolitarius ― South America.
    • Among the eagles are some of the largest birds of prey: only the condors and some of the Old World vultures are markedly larger. It is regularly debated which should be considered the largest species of eagle. They could be measured variously in total length, body mass, or wingspan. Different lifestyle needs among various eagles result in variable measurements from species to species. For example, many forest-dwelling eagles, including the very large harpy eagle, have relatively short wingspans, a feature necessary for being able to maneuver in quick, short bursts through densely forested habitats.[7] Eagles in the genus Aquila, though found almost strictly in open country, are superlative soarers, and have relatively long wings for their size.[7]

      These lists of the top five eagles are based on weight, length, and wingspan, respectively. Unless otherwise noted by reference, the figures listed are the median reported for each measurement in the guide Raptors of the World[11] in which only measurements that could be personally verified by the authors were listed.[7]

      Rank Common name Scientific name Body mass
      1 Steller’s sea eagle Haliaeetus pelagicus 6.7 kilograms (15 lb)
      2 Philippine eagle Pithecophaga jefferyi 6.35 kg (14.0 lb)
      3 Harpy eagle Harpia harpyja 5.95 kg (13.1 lb)
      4 White-tailed eagle Haliaeetus albicilla 4.8 kg (11 lb)[12]
      5 Martial eagle Polemaetus bellicosus 4.6 kg (10 lb)[12]
      Rank Common name Scientific name Total length
      1 Philippine eagle Pithecophaga jefferyi 100 cm (3 ft 3 in)[13]
      2 Harpy eagle Harpia harpyja 98.5 cm (3 ft 3 in)
      3 Wedge-tailed eagle Aquila audax 95.5 cm (3 ft 2 in)
      4 Steller’s sea eagle Haliaeetus pelagicus 95 cm (3 ft 1 in)
      5 Crowned eagle Stephanoaetus coronatus 87.5 cm (2 ft 10 in)
      Rank Common name Scientific name Median wingspan
      1 Philippine eagle Pithecophaga jefferyi 220 cm (7 ft 3 in)
      2 White-tailed eagle Haliaeetus albicilla 218.5 cm (7 ft 2 in)
      3 Steller’s sea eagle Haliaeetus pelagicus 212.5 cm (7 ft 0 in)
      4 Wedge-tailed eagle Aquila audax 210 cm (6 ft 11 in)[14][15]
      5 Golden eagle Aquila chrysaetos 207 cm (6 ft 9 in)
      6 Martial eagle Polemaetus bellicosus 206.5 cm (6 ft 9 in)