Eagle is the common name for certain large predatory birds of prey within the family of the Accipitridae. While on a genetic level, only the subfamily Aquilinae comprises "true eagles", many other species are commonly referred to as eagles, such as the bald eagle, and the term generally carries no taxonomic weight. Most of the 68 species of eagles are from Eurasia and Africa. Outside this area, just 14 species can be found—two in North America, nine in Central and South America, and three in Australia.
Eagles are not a natural group but denote essentially any kind of bird of prey large enough to hunt sizeable (about 50 cm long or more overall) vertebrates.
Etymology The word "eagle" is borrowed into English from Old French aigle, ultimately from Latin aquila. It is cognate with terms such as French aigle, Portuguese águia and Spanish águila. Historically, the native English term for eagle was "ern" (), derived from Proto-Germanic *arnuz, and thus cognate with other synonymous words in Germanic languages such as German Aar, Dutch arend, Swedish örn and Gothic 𐌰𐍂𐌰 (). The term "ern" or "erne" is still used in Modern English in reference to some larger species of eagle, in particular the fish eagles. While some ornithologists may favor this term as a way to distinguish fish eagles from true eagles, all species of fish eagle (such as the bald eagle and white-tailed eagle) are still commonly referred to as "eagles".
Description Eagles are large, powerfully-built birds of prey, with heavy heads and beaks. Even the smallest eagles, such as the booted eagle (Hieraaetus pennatus), 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 their aerodynamic feathers. Most eagles are larger than any other raptors, apart from some vultures. The smallest species of eagle is the Great Nicobar serpent eagle (Spilornis klossi), at and . 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 wedge-tailed eagle has a visual acuity twice that of a typical human. This acuity enables eagles to spot potential prey from a very long distance. This keen eyesight is primarily attributed to their extremely large pupils which ensure minimal diffraction (scattering) of the incoming light. Like most diurnal raptors, eagles have little ability to see ultraviolet light. The female of all known species of eagles is larger than the male.
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 parents take no action to stop the killing. It is said that eagles fly above clouds but this is not true. Eagles fly during storms and glide from the wind's pressure. This saves the bird's energy. 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 Icthyophaga 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 Circaetus, Terathopius, 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 forests. 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 on 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.
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 mule deer fawn. 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 and a martial eagle even killed a duiker, 7–8 times heavier than the preying eagle. Authors on birds David Allen Sibley, Pete 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):
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. Eagles in the genus Aquila, found almost exclusively in open country, are noted for their ability to soar, and have relatively long wings for their size.
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 WorldFerguson-Lees, et al. in which only measurements that could be personally verified by the authors were listed.
Rank Common name Scientific name Body mass 1 Steller's sea eagle Haliaeetus pelagicus (Average Weight) 2 Harpy eagle Harpia harpyja (Average Weight) 3 Philippine eagle Pithecophaga jefferyi (Average Weight) 4 White-tailed eagle Haliaeetus albicilla (Average Weight) 5 Martial eagle Polemaetus bellicosus (Average Weight)
Rank Common name Scientific name Total length 1 Philippine eagle Pithecophaga jefferyi 2 Harpy eagle Harpia harpyja 3 Wedge-tailed eagle Aquila audax 4 Steller's sea eagle Haliaeetus pelagicus 5 Crowned eagle Stephanoaetus coronatus
Rank Common name Scientific name Median wingspan 1 White-tailed eagle Haliaeetus albicilla 2 Steller's sea eagle Haliaeetus pelagicus 3 Wedge-tailed eagle Aquila audax 4 Golden eagle Aquila chrysaetos 5 Martial eagle Polemaetus bellicosus
Habitat The eagles are generally distributed in all types of habitats and nearly all parts of the world. The birds can be found in northern tundra to tropical rainforests and deserts. In North America, bald eagles and golden eagles are very common.
Distribution Australasian Australia: wedge-tailed eagle (range extends into southern New Guinea), white-bellied sea-eagle (range extends into Asia), little eagle. New Guinea: Papuan eagle, white-bellied sea-eagle, pygmy eagle. Nearctic (USA and Canada): golden eagle (also found in Palearctic), bald eagle. Neotropical (Central and South America): Spizaetus (four species), solitary eagles (two spp.), harpy eagle, crested eagle, black-chested buzzard-eagle. Palearctic (Europe, Northern Africa, Asia without South Asia and Southeast Asia) Eurasia: Golden eagle, White-tailed eagle. Subsaharan Africa: African fish eagle, Martial Eagle, Crowned eagle, Verreaux's eagle, Tawny eagle, Long-crested eagle
Groups Eagles are often informally divided into four groups. from
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 proposed separating the eagle groups into their own subfamilies of Accipitridae.
Fish eagles Fish eagles (or sea eagles) take fish as a large part of their diets, either fresh or as carrion.
Some authors include Gypohierax angolensis, the "vulturine fish eagle" (also called the palm-nut vulture) in this group. However, genetic analyses indicate it is related to a grouping of Neophron–Gypaetus–Eutriorchis (Egyptian vulture, bearded vulture (lammergeier), and Madagascar serpent eagle).
The fish eagles have a close genetic relationship with Haliastur and Milvus; the whole group is only distantly related to the Buteo group.
Fish eagles exist in every continent throughout the world, except for South America.
Although fish eagles can be found in many different places around the world, they have been classified as "Near Threatened". Reasons such as overfishing, pollution, habitat destruction, and the use of pesticides have contributed to the species' rapid population drop.
Booted eagles
Booted eagles or "true eagles" have feathered tarsi (lower legs).
Tribe Aquililae or proposed subfamily Aquilinae. Genera: Aquila, Hieraaetus; Spizaetus, Oroaetus, Spizastur; Nisaetus; Ictinaetus, Lophoaetus; Polemaetus; and Stephanoaetus.
See comments under eagle species for changes to the composition of these genera.
Snake eagles Most snake or serpent eagles, as the name suggests, primarily prey on snakes.
Subfamily Circaetinae. Genera: Circaetus, Spilornis, Dryotriorchis, Terathopius. Eutriorchis (subfamily Gypaetinae or Circaetinae).
Despite filling the niche of a snake eagle, genetic studies suggest that the Madagascar serpent eagle (Eutriorchis) is not related to them.
Over several decades, a great deal of research has been done on the Snake-eagle's diet, which is mainly made up of reptiles, especially snakes. When it comes to catching snakes, it is generally accepted that the bird exhibits generalist feeding behavior, which means it does not hunt down specific types of snakes but rather feeds on them depending on their availability in the wild.
Harpy eagles Harpy eagles or "giant forest eagles" 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, 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 harpyja, harpy eagle ― Central and South America. Morphnus guianensis, crested eagle ― Central and South America. Harpyopsis novaeguineae, Papuan eagle ― New Guinea. Philippine eagle Pithecophaga jefferyi, Philippine eagle ― Philippines. Solitary eagles Chaco eagle or crowned solitary eagle, Buteogallus (formerly Harpyhaliaetus) coronatus ― South America. Solitary eagle or montane solitary eagle, Buteogallus (formerly Harpyhaliaetus) solitarius ― South America.
Species
Major new research into eagle taxonomy suggests that the important genera Aquila and Hieraaetus are not composed of nearest relatives, and it is likely that a reclassification of these genera will soon take place, with some species being moved to Lophaetus or Ictinaetus. Bonelli's eagle and the African hawk-eagle have been moved from Hieraaetus to Aquila.