Eagle

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.

Eagle
Bald eagle
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Aves
Order:
Accipitriformes
Family:
Accipitridae
Golden eagle

Description

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 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 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 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):[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.[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
1Steller's sea eagleHaliaeetus pelagicus6.7 kilograms (15 lb)
2Philippine eaglePithecophaga jefferyi6.35 kg (14.0 lb)
3Harpy eagleHarpia harpyja5.95 kg (13.1 lb)
4White-tailed eagleHaliaeetus albicilla4.8 kg (11 lb)[12]
5Martial eaglePolemaetus bellicosus4.6 kg (10 lb)[12]
Rank Common name Scientific name Total length
1Philippine eaglePithecophaga jefferyi100 cm (3 ft 3 in)[13]
2Harpy eagleHarpia harpyja98.5 cm (3 ft 3 in)
3Wedge-tailed eagleAquila audax95.5 cm (3 ft 2 in)
4Steller's sea eagleHaliaeetus pelagicus95 cm (3 ft 1 in)
5Crowned eagleStephanoaetus coronatus87.5 cm (2 ft 10 in)
Rank Common name Scientific name Median wingspan
1White-tailed eagleHaliaeetus albicilla218.5 cm (7 ft 2 in)
2Steller's sea eagleHaliaeetus pelagicus212.5 cm (7 ft 0 in)
3Wedge-tailed eagleAquila audax210 cm (6 ft 11 in)[14][15]
4Golden eagleAquila chrysaetos207 cm (6 ft 9 in)
5Martial eaglePolemaetus bellicosus206.5 cm (6 ft 9 in)

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

Eurasia: Golden eagle,[16] White-tailed eagle.

Groups

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: Haliaeetus, Ichthyophaga.

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 Neophron–Gypaetus–Eutriorchis (Egyptian vulture, bearded 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: Aquila, Hieraaetus; Spizaetus, Oroaetus, Spizastur; Nisaetus;[20] Ictinaetus, Lophoaetus; Polemaetus; 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: Circaetus, Spilornis, Dryotriorchis, Terathopius.[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 harpyja, harpy eagle ― Central and South America.
    • Morphnus guianensis, crested eagle ― Central and South America.
    • Harpyopsis novaeguineae, Papuan eagle ― New Guinea.
  • Philippine eagle
  • 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
Martial eagle in Namibia.
Philippine eagle, Pithecophaga jefferyi in Southern Philippines.
Wedge-tailed eagle in Australia.
Eastern imperial eagle – in Israel

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.[19]

  • Bonelli's eagle and the African hawk-eagle have been moved from Hieraaetus to Aquila.
  • Either the greater spotted eagle and lesser spotted eagle should move from Aquila to join the long-crested eagle in Lophaetus, or, perhaps better, all three of these species should move to Ictinaetus with the black eagle.
  • The steppe eagle and tawny eagle, once thought to be conspecific, are not even each other's nearest relatives.

Family Accipitridae

  • Subfamily Buteoninae – hawks (buzzards), true eagles and seaeagles
    • Genus Geranoaetus
      • Black-chested buzzard-eagle, Geranoaetus melanoleucus
    • Genus Harpyhaliaetus
      • Chaco eagle, Harpyhaliaetus coronatus
      • Solitary eagle, H. solitarius
    • Genus Morphnus
      • Crested eagle, Morphnus guianensis
    • Genus Harpia
      • Harpy eagle, Harpia harpyja
    • Genus Pithecophaga
    • Genus Harpyopsis
      • Papuan eagle, Harpyopsis novaeguineae
    • Genus Spizaetus
      • Black hawk-eagle, S. tyrannus
      • Ornate hawk-eagle, S. ornatus
      • Black-and-white hawk-eagle, S. melanoleucus – formerly Spizastur
      • Black-and-chestnut eagle, S. isidori – formerly Oroaetus
    • Genus Nisaetus – previously included in Spizaetus
      • Changeable hawk-eagle, N. cirrhatus
        • Flores hawk-eagle N. floris – earlier a subspecies, S. c. floris
      • Sulawesi hawk-eagle, N. lanceolatus
      • Mountain hawk-eagle, N. nipalensis
        • Legge's hawk-eagle, Nisaetus kelaarti – previously a race of S. nipalensis
      • Blyth's hawk-eagle, N. alboniger
      • Javan hawk-eagle, N. bartelsi
      • (Northern) Philippine hawk-eagle, N. philippensis
        • Pinsker's hawk-eagle (Southern Philippine hawk-eagle), Nisaetus pinskeri – earlier S. philippensis pinskeri
      • Wallace's hawk-eagle, N. nanus
    • Genus Lophaetus
      • Long-crested eagle, Lophaetus occipitalis – possibly belongs in Ictinaetus
    • Genus Stephanoaetus
      • Crowned eagle, Stephanoaetus coronatus
      • Malagasy crowned eagle, Stephanoaetus mahery (extinct)
    • Genus Polemaetus
      • Martial eagle, Polemaetus bellicosus
    • Genus Hieraaetus
      • Ayres's hawk-eagle, H. ayresii
      • Little eagle, H. morphnoides
      • Pygmy eagle, H. weiskei – previously subspecies H. m. weiskei
      • Booted eagle, H. pennatus
    • Genus Harpagornis (extinct)
      • Haast's eagle, †Harpagornis moorei – possibly belongs in either Hieraaetus or Aquila[22]
    • Genus Lophotriorchis
      • Rufous-bellied eagle, L. kienerii
        A steppe eagle in Lahore Zoo, Pakistan
    • Genus Aquila
      • Bonelli's eagle, Aquila fasciata – formerly Hieraaetus fasciatus
      • African hawk-eagle, A. spilogaster – formerly in Hieraaetus
      • Cassin's hawk-eagle, A. africana – formerly in Hieraaetus or Spizaetus genera
      • Golden eagle, A. chrysaetos
      • Eastern imperial eagle, A. heliaca
      • Spanish imperial eagle A. adalberti
      • Steppe eagle, A. nipalensis
      • Tawny eagle, A. rapax
      • Greater spotted eagle, A. clanga – to be moved to Lophaetus or Ictinaetus
      • Lesser spotted eagle, A. pomarina – to be moved to Lophaetus or Ictinaetus
      • Indian spotted eagle, A. hastata – to be moved to Lophaetus or Ictinaetus
      • Verreaux's eagle, A. verreauxii
      • Gurney's eagle, A. gurneyi
      • Wahlberg's eagle, A. wahlbergi – to be moved to Hieraaetus
      • Wedge-tailed eagle, A. audax
    • Genus Ictinaetus
      • Black eagle, Ictinaetus malayensis
    • Genus Haliaeetus
      • White-tailed eagle, Haliaeetus albicilla
      • Bald eagle, H. leucocephalus
      • Steller's sea eagle, H. pelagicus
      • African fish eagle, H. vocifer
      • White-bellied sea eagle, H. leucogaster
      • Sanford's sea eagle, H. sanfordi
      • Madagascar fish eagle, H. vociferoides
      • Pallas' sea eagle, H. leucoryphus
    • Genus Ichthyophaga
      • Lesser fish eagle, Ichthyophaga humilis
      • Grey-headed fish eagle, I. ichthyaetus
Short-toed snake eagle in flight
  • Subfamily Circaetinae: snake-eagles
    • Genus Terathopius
      • Bateleur, Terathopius ecaudatus
    • Genus Circaetus
      • Short-toed snake eagle, Circaetus gallicus
      • Black-chested snake eagle, C. pectoralis
      • Brown snake eagle, C. cinereus
      • Fasciated snake eagle, C. fasciolatus
      • Western banded snake eagle, C. cinerascens
    • Genus Dryotriorchis
      • Congo serpent eagle, D. spectabilis
    • Genus Spilornis
      • Crested serpent eagle, Spilornis cheela
        • Central Nicobar serpent eagle, S. minimus (subspecies or species)
      • Great Nicobar serpent eagle, S. klossi
      • Mountain serpent eagle, S. kinabaluensis
      • Sulawesi serpent eagle, S. rufipectus
      • Philippine serpent eagle, S. holospilus
      • Andaman serpent eagle, S. elgini
    • Genus Eutriorchis
      • Madagascar serpent eagle, Eutriorchis astur

In culture
Eagles, a Chinese Ming period painting. Located at the National Palace Museum

Etymology

The modern English term for the bird is derived from Latin: aquila by way of French: aigle. The origin of aquila is unknown, but it is believed to possibly derive from either aquilus (meaning dark-colored, swarthy, or blackish) as a reference to the plumage of eagles or from aquilo (meaning north wind).

Old English used the term earn, related to Scandinavia's ørn/örn. It is similar to other Indo-European terms for "bird" or "eagle", including Greek: ὄρνις (ornís), Russian: орёл (orël), and Welsh: eryr.

The sculpture of eagle at the top of the fountain at Plac Orła Białego in Szczecin, Poland

In Britain before 1678, eagle referred specifically to the golden eagle, with the other native species, the white-tailed eagle, being known as erne. The modern name "golden eagle" for aquila chrysaetos was introduced by the naturalist John Ray.

Religion and folklore
Representation of an eagle at Rio Carnival, 2014
Garuda, the Vahana of Lord Vishnu, depicted with an eagle's beak and wings

In ancient Sumerian mythology, the mythical king Etana was said to have been carried into heaven by an eagle.[23] Classical writers such as Lucan and Pliny the Elder claimed that the eagle was able to look directly at the sun, and that they forced their fledglings to do the same. Those that blinked would be cast from the nest. This belief persisted until the Medieval era.[24]

The eagle is the patron animal of the ancient Greek god Zeus. In particular, Zeus was said to have taken the form of an eagle in order to abduct Ganymede, and there are numerous artistic depictions of the eagle Zeus bearing Ganymede aloft, from Classical times up to the present (see illustrations in the Ganymede (mythology) page.)[25]

Psalm 103 (in Greek, Latin, and English) mentions renewing one's youth "as the eagle" (although the Hebrew word נשר apparently means vulture). Augustine of Hippo gives a curious explanation of this in his commentary on the Psalms.[26]

The eagle is a common form in the Anglican tradition, often used to support the Bible because of the symbolism of spreading the gospel over the world. Additional symbolic meanings for "eagle" include the pronouncements to the Israelites in Exodus 19:4; Psalms 103:5 and Isaiah 40:31. The United States eagle feather law stipulates that only individuals of certifiable Native American ancestry enrolled in a federally recognized tribe are legally authorized to obtain eagle feathers for religious or spiritual reasons.[27] In Canada, the poaching of eagle feathers for the booming U.S. market has sometimes resulted in the arrests of First Nations person for the crime.[28]

The Moche people of ancient Peru worshiped the eagle and often depicted eagles in their art.[29]

Heraldry
Coat of Arms of Austria

Eagles are an exceptionally common symbol in heraldry, being considered the "King of Birds" in contrast to the lion, the "King of Beasts". Whereas the lion (e.g. England) usually represents a kingdom, the eagle is symbolic for an empire. They are particularly popular in Germanic countries such as Austria, due to their association with the Holy Roman Empire. The eagle of the Holy Roman Empire was two-headed, supposedly representing the two divisions, East and West, of the old Roman Empire. This motif, derived from the Byzantine (Eastern Roman) Empire was also adopted by the Russian Empire and is still featured in the Flag of Albania. The Roman eagle was preceded by the eagle of Ptolemaic Egypt and the Achaemenid Empire.

Heraldic eagles are most often found displayed, i.e. with their wings and legs extended. They can also occur close, i.e. with their wings folded, or rising, i.e. about to take flight. The heads, wings, and legs of eagles can also be found independently.

Notes
  1. "There are four major groups of eagles: fish eagles, booted eagles, snake eagles and giant forest eagles."[17]

References
  1. del Hoyo, J.; Elliot, A. & Sargatal, J. (editors). (1994). Handbook of the Birds of the World Volume 2: New World Vultures to Guineafowl. Lynx Edicions. ISBN 84-87334-15-6
  2. Shlaer, Robert (1972). "An Eagle's Eye: Quality of the Retinal Image" (PDF). Science. 176 (4037): 920–922. Bibcode:1972Sci...176..920S. doi:10.1126/science.176.4037.920. PMID 5033635. Archived from the original (PDF) on 30 November 2012. Retrieved 16 April 2012.
  3. Leclerc, Georges; Louis, Comte de Buffon (2010). The Natural History of Birds: From the French of the Count de Buffon; Illustrated with Engravings, and a Preface, Notes, and Additions, by the Translator. Cambridge University Press. pp. 60–. ISBN 978-1-108-02298-9. Archived from the original on 29 April 2016.
  4. Grambo, Rebecca L. (2003). Eagles. Voyageur Press. ISBN 978-0-89658-363-4. Archived from the original on 30 April 2016.
  5. Grambo, Rebecca L (2003). Eagles. Voyageur Press. p. 32. ISBN 978-0-89658-363-4.
  6. Stinson, Christopher H (1979). "On the Selective Advantage of Fratricide in Raptors". Evolution. 33 (4): 1219–1225. doi:10.2307/2407480. JSTOR 2407480. PMID 28563923.
  7. Ferguson-Lees, J.; Christie, D. (2001). Raptors of the World. London: Christopher Helm. ISBN 0-7136-8026-1.
  8. "Amazing Bird Records". Trails.com. Archived from the original on 20 June 2017. Retrieved 20 July 2012.
  9. Watson, Jeff (2011). The Golden Eagle (Second ed.). ISBN 978-0-30017-019-1.
  10. Sutton, C.; Dunne, P.; Sibley, D. (1989). Hawks in Flight: The Flight Identification of North American Migrant Raptors. Boston: Houghton Mifflin Harcourt. ISBN 0-3955-1022-8.
  11. Ferguson-Lees, et al.)
  12. del Hoyo, J; Elliot, A; Sargatal, J (1996). Handbook of the Birds of the World. 3. Barcelona: Lynx Edicions. ISBN 84-87334-20-2.
  13. Gamauf, A.; Preleuthner, M. & Winkler, H. (1998). "Philippine Birds of Prey: Interrelations among habitat, morphology and behavior" (PDF). The Auk. 115 (3): 713–726. doi:10.2307/4089419. JSTOR 4089419. Archived (PDF) from the original on 23 August 2014.
  14. Morgan, A.M. "The spread and weight of the Wedge-tailed Eagle" (PDF). South Australian Ornithologist. 11: 156–157. Archived from the original (PDF) on 24 April 2013.
  15. Wood, Gerald (1983). The Guinness Book of Animal Facts and Feats. ISBN 978-0-85112-235-9.
  16. "European Raptors: Golden Eagle". www.europeanraptors.org (in German). Archived from the original on 7 May 2017. Retrieved 11 September 2017.
  17. Stalcup, Carolyn. "All About Eagles". The American Eagle Foundation. Archived from the original on 14 July 2014. Retrieved 25 May 2014.
  18. Rutledge, Hope. "Eagles of the World". American Bald Eagle Information. Archived from the original on 28 May 2014. Retrieved 11 June 2014. from Grambo, Rebecca L. (1999). Eagles. Voyageur Press, Inc.
  19. Lerner, H. R. L.; 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. doi:10.1016/j.ympev.2005.04.010. PMID 15925523.
  20. Lerner, Heather R. L.; Mindell, David P. (9 May 2006). "Accipitridae". The Tree of Life Web Project. Archived from the original on 23 December 2014.
  21. Bouglouan, Nicole. "The booted eagles throughout the world: introduction". Oiseaux-birds. Archived from the original on 17 May 2014. Retrieved 11 June 2014.
  22. Bunce, M.; et al. (2005). "Ancient DNA Provides New Insights into the Evolutionary History of New Zealand's Extinct Giant Eagle". PLoS Biol. 3 (1): e9. doi:10.1371/journal.pbio.0030009. PMC 539324. PMID 15660162.
  23. Horowitz, Wayne (1998). Mesopotamian Cosmic Geography. Winona Lake, Indiana: Eisenbrauns. pp. 43–59. ISBN 0-931464-99-4. Archived from the original on 6 December 2017.CS1 maint: ref=harv (link)
  24. Badke, David. The Medieval Bestiary Archived 22 November 2016 at the Wayback Machine
  25. Hutchinson, John (1749). Philosophical and Theological Works of the Late Truly Learned John Hutchinson. London, UK: James Hidges. p. 402. Archived from the original on 25 April 2016.
  26. Psalm 103 Archived 8 May 2015 at the Wayback Machine in Augustine's commentary.
  27. Office of Law Enforcement. "National Eagle Repository". Mountain-Prairie Region. United States Fish and Wildlife Service. Archived from the original on 10 October 2007. Retrieved 20 November 2007.
  28. Sin, Lena (30 April 2006). "Charges laid in eagle-poaching case". The Province. CanWest MediaWorks Publications Inc. Archived from the original on 31 May 2009. Retrieved 20 November 2007.
  29. Larco Herrera, Rafael and Berrin, Kathleen (1997) The Spirit of Ancient Peru Thames and Hudson, New York, ISBN 0500018022

Further reading
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