Birds of prey or predatory birds, also known as (although not the same as) raptors, are hypercarnivorousbirdspecies that actively hunt and feed on other vertebrates (mainly mammals, reptiles and other smaller birds). In addition to speed and strength, these predators have keen eyesight for detecting prey from a distance or during flight, strong feet with sharp talons for grasping or killing prey, and powerful, curved beaks for tearing off flesh.[2][3][4] Although predatory birds primarily hunt live prey, many species (such as fish eagles, vultures and condors) also scavenge and eat carrion.[2]
The term raptor is derived from the Latin word rapio, meaning "to seize or take by force".[8] The common names for various birds of prey are based on structure, but many of the traditional names do not reflect the evolutionary relationships between the groups.[citation needed]
Variations in shape and size
Eagles tend to be large, powerful birds with long, broad wings and massive feet. Booted eagles have legs and feet feathered to the toes and build very large stick nests.
Falcons and kestrels are medium-size birds of prey with long pointed wings, and many are particularly swift flyers. They belong to the family Falconidae, only distantly related to the Accipitriformes below. Caracaras are a distinct subgroup of the Falconidae unique to the New World, and most common in the Neotropics – their broad wings, naked faces and appetites of a generalist suggest some level of convergence with either Buteo or the vulturine birds, or both.
True hawks are medium-sized birds of prey that usually belong to the genus Accipiter (see below). They are mainly woodland birds that hunt by sudden dashes from a concealed perch. They usually have long tails for tight steering.
Buzzards are medium-large raptors with robust bodies and broad wings, or, alternatively, any bird of the genus Buteo (also commonly known as "hawks" in North America, while "buzzard" is colloquially used for vultures).
Harriers are large, slender hawk-like birds with long tails and long thin legs. Most use a combination of keen eyesight and hearing to hunt small vertebrates, gliding on their long broad wings and circling low over grasslands and marshes.
Kites have long wings and relatively weak legs. They spend much of their time soaring. They will take live vertebrate prey, but mostly feed on insects or even carrion.
The osprey, a single species found worldwide that specializes in catching fish and builds large stick nests.
Owls are variable-sized, typically night-specialized hunting birds. They fly almost silently due to their special feather structure that reduces turbulence. They have particularly acute hearing and nocturnal eyesight.
The secretarybird is a single species with a large body and long, stilted legs endemic to the open grasslands of Sub-Saharan Africa.
Many of these English language group names originally referred to particular species encountered in Britain. As English-speaking people travelled further, the familiar names were applied to new birds with similar characteristics. Names that have generalised this way include: kite (Milvus milvus), sparrowhawk or sparhawk (Accipiter nisus), goshawk (Accipiter gentilis), kestrel (Falco tinninculus), hobby (Falco subbuteo), harrier (simplified from "hen-harrier", Circus cyaneus), buzzard (Buteo buteo).
Some names have not generalised, and refer to single species (or groups of closely related (sub)species), such as the merlin (Falco columbarius).
Systematics
Historical classifications
The taxonomy of Carl Linnaeus grouped birds (class Aves) into orders, genera, and species, with no formal ranks between genus and order. He placed all birds of prey into a single order, Accipitres, subdividing this into four genera: Vultur (vultures), Falco (eagles, hawks, falcons, etc.), Strix (owls), and Lanius (shrikes). This approach was followed by subsequent authors such as Gmelin, Latham and Turton.
Louis Pierre Vieillot used additional ranks: order, tribe, family, genus, species. Birds of prey (order Accipitres) were divided into diurnal and nocturnal tribes; the owls remained monogeneric (family Ægolii, genus Strix), whilst the diurnal raptors were divided into three families: Vulturini, Gypaëti, and Accipitrini.[9] Thus Vieillot's families were similar to the Linnaean genera, with the difference that shrikes were no longer included amongst the birds of prey. In addition to the original Vultur and Falco (now reduced in scope), Vieillot adopted four genera from Savigny: Phene, Haliæetus, Pandion, and Elanus. He also introduced five new genera of vultures (Gypagus, Catharista, Daptrius, Ibycter, Polyborus)[note 1] and eleven new genera of accipitrines (Aquila, Circaëtus, Circus, Buteo, Milvus, Ictinia, Physeta, Harpia, Spizaëtus, Asturina, Sparvius).
Falconimorphae is a deprecated superorder within Raptores, formerly composed of the orders Falconiformes and Strigiformes. The clade was invalidated after 2012. Falconiformes is now placed in Eufalconimorphae, while Strigiformes is placed in Afroaves.[10]
The order Accipitriformes is believed to have originated 44million years ago when it split from the common ancestor of the secretarybird (Sagittarius serpentarius) and the accipitrid species.[11] The phylogeny of Accipitriformes is complex and difficult to unravel. Widespread paraphylies were observed in many phylogenetic studies.[12][13][14][15][16] More recent and detailed studies show similar results.[17] However, according to the findings of a 2014 study, the sister relationship between larger clades of Accipitriformes was well supported (e.g. relationship of Harpagus kites to buzzards and sea eagles and these latter two with Accipiter hawks are sister taxa of the clade containing Aquilinae and Harpiinae).[11]
The diurnal birds of prey are formally classified into six families of two different orders (Accipitriformes and Falconiformes).
Cathartidae: New World vultures, including condors
These families were traditionally grouped together in a single order Falconiformes but are now split into two orders, the Falconiformes and Accipitriformes. The Cathartidae are sometimes placed in a separate order Cathartiformes. Formerly, they were sometimes placed in the order Ciconiiformes.
The secretary bird and/or osprey are sometimes listed as subfamilies of Acciptridae: Sagittariinae and Pandioninae, respectively.
Below is a simplified phylogeny of Telluraves which is the clade where the birds of prey belong to along with passerines and several near-passerine lineages.[18][10][19] The orders in bold text are birds of prey orders; this is to show the paraphyly of the group as well as their relationships to other birds.
A recent phylogenomic study from Wu et al. (2024) has found an alternative phylogeny for the placement of the birds of prey. Their analysis has found support in a clade consisting of the Strigiformes and Accipitriformes in new clade Hieraves. Hieraves was also recovered to be the sister clade to Australaves (which it includes the Cariamiformes and Falconiformes along with Psittacopasserae). Below is their phylogeny from the study.[20]
Cariamiformes is an order of telluravian birds consisting of the living seriemas and extinct terror birds. Jarvis et al. 2014 suggested including them in the category of birds of prey,[21] and McClure et al. 2019 considered seriemas to be birds of prey.[1]The Peregrine Fund also considers seriemas to be birds of prey.[22] Like most birds of prey, seriemas and terror birds prey on vertebrates.
However, seriemas were not traditionally considered birds of prey. There were traditionally classified in the order Gruiformes. And they are still not considered birds of prey in general parlance. Their bodies are also shaped completely differently from birds of prey. They have long legs and long necks. While secretarybirds also have long legs, they otherwise resemble raptors. Seriemas do not. Their beak is hooked, but too long.
Migration
Migratory behaviour evolved multiple times within accipitrid raptors.
The earliest event occurred nearly 14 to 12million years ago. This result seems to be one of the oldest dates published so far in the case of birds of prey.[11] For example, a previous reconstruction of migratory behaviour in one Buteo clade[16] with a result of the origin of migration around 5million years ago was also supported by that study.
Migratory species of raptors may have had a southern origin because it seems that all of the major lineages within Accipitridae had an origin in one of the biogeographic realms of the Southern Hemisphere. The appearance of migratory behaviour occurred in the tropics parallel with the range expansion of migratory species to temperate habitats.[11] Similar results of southern origin in other taxonomic groups can be found in the literature.[23][24][25]
Distribution and biogeographic history highly determine the origin of migration in birds of prey. Based on some comparative analyses, diet breadth also has an effect on the evolution of migratory behaviour in this group,[11] but its relevance needs further investigation. The evolution of migration in animals seems to be a complex and difficult topic with many unanswered questions.
A recent study discovered new connections between migration and the ecology, life history of raptors. A brief overview from abstract of the published paper shows that "clutch size and hunting strategies have been proved to be the most important variables in shaping distribution areas, and also the geographic dissimilarities may mask important relationships between life history traits and migratory behaviours. The West Palearctic-Afrotropical and the North-South American migratory systems are fundamentally different from the East Palearctic-Indomalayan system, owing to the presence versus absence of ecological barriers."[26] Maximum entropy modelling can help in answering the question: why species winters at one location while the others are elsewhere. Temperature and precipitation related factors differ in the limitation of species distributions. "This suggests that the migratory behaviours differ among the three main migratory routes for these species"[26] which may have important conservational consequences in the protection of migratory raptors.
Birds of prey (raptors) are known to display patterns of sexual dimorphism. It is commonly believed that the dimorphisms found in raptors occur due to sexual selection or environmental factors. In general, hypotheses in favor of ecological factors being the cause for sexual dimorphism in raptors are rejected. This is because the ecological model is less parsimonious, meaning that its explanation is more complex than that of the sexual selection model. Additionally, ecological models are much harder to test because a great deal of data is required.[27]
Dimorphisms can also be the product of intrasexual selection between males and females. It appears that both sexes of the species play a role in the sexual dimorphism within raptors; females tend to compete with other females to find good places to nest and attract males, and males competing with other males for adequate hunting ground so they appear as the most healthy mate.[28] It has also been proposed that sexual dimorphism is merely the product of disruptive selection, and is merely a stepping stone in the process of speciation, especially if the traits that define gender are independent across a species. Sexual dimorphism can be viewed as something that can accelerate the rate of speciation.[29]
In non-predatory birds, males are typically larger than females. However, in birds of prey, the opposite is the case. For instance, the kestrel is a type of falcon in which males are the primary providers, and the females are responsible for nurturing the young. In this species, the smaller the kestrels are, the less food is needed and thus, they can survive in environments that are harsher. This is particularly true in the male kestrels. It has become more energetically favorable for male kestrels to remain smaller than their female counterparts because smaller males have an agility advantage when it comes to defending the nest and hunting. Larger females are favored because they can incubate larger numbers of offspring, while also being able to brood a larger clutch size.[30]
Olfaction
It is a long-standing belief that birds lack any sense of smell, but it has become clear that many birds do have functional olfactory systems. Despite this, most raptors are still considered to primarily rely on vision, with raptor vision being extensively studied. A 2020 review of the existing literature combining anatomical, genetic, and behavioural studies showed that, in general, raptors have functional olfactory systems that they are likely to use in a range of different contexts.[31]
Persecution
Birds of prey have been historically persecuted both directly and indirectly. In the Danish Faroe Islands, there were rewards Naebbetold (by royal decree from 1741) given in return for the bills of birds of prey shown by hunters. In Britain, kites and buzzards were seen as destroyers of game and killed, for instance in 1684–5 alone as many as 100 kites were killed. Rewards for their killing were also in force in the Netherlands from 1756. From 1705 to 1800, it has been estimated that 624087 birds of prey were killed in a part of Germany that included Hannover, Luneburg, Lauenburg and Bremen with 14125 claws deposited just in 1796–97.[32] Many species also develop lead poisoning after accidental consumption of lead shot when feeding on animals that had been shot by hunters.[33] Lead pellets from direct shooting that the birds have escaped from also cause reduced fitness and premature deaths.[34]
Attacks on humans
Some evidence supports the contention that the African crowned eagle occasionally views human children as prey, with a witness account of one attack (in which the victim, a seven-year-old boy, survived and the eagle was killed),[35] and the discovery of part of a human child skull in a nest. This would make it the only living bird known to prey on humans, although other birds such as ostriches and cassowaries have killed humans in self-defense and a lammergeier might have killed Aeschylus by accident.[36] Many stories of Brazilian indigenous peoples speak about children mauled by Uiruuetê, the Harpy Eagle in Tupi language.[citation needed] Various large raptors like golden eagles are reported attacking human beings,[37] but its unclear if they intend to eat them or if they have ever been successful in killing one.
Some fossil evidence indicates large birds of prey occasionally preyed on prehistoric hominids. The Taung Child, an early human found in Africa, is believed to have been killed by an eagle-like bird similar to the crowned eagle. The Haast's eagle may have preyed on early humans in New Zealand, and this conclusion would be consistent with Maori folklore. Leptoptilos robustus[38] might have preyed on both Homo floresiensis and anatomically modern humans, and the Malagasy crowned eagle, teratorns, Woodward's eagle and Caracara major[39] are similar in size to the Haast's eagle, implying that they similarly could pose a threat to a human being.
Vision
Birds of prey have incredible vision and rely heavily on it for a number of tasks.[40] They utilize their high visual acuity to obtain food, navigate their surroundings, distinguish and flee from predators, mating, nest construction, and much more. They accomplish these tasks with a large eye in relation to their skull, which allows for a larger image to be projected onto the retina.[40] The visual acuity of some large raptors such as eagles and Old World vultures are the highest known among vertebrates; the wedge-tailed eagle has twice the visual acuity of a typical human and six times that of the common ostrich, the vertebrate with the largest eyes.[41]
There are two regions in the retina, called the deep and shallow fovea, that are specialized for acute vision.[42] These regions contain the highest density of photoreceptors, and provide the highest points of visual acuity. The deep fovea points forward at an approximate 45° angle, while the shallow fovea points approximately 15° to the right or left of the head axis.[42] Several raptor species repeatedly cock their heads into three distinct positions while observing an object. First, is straight ahead with their head pointed towards the object. Second and third are sideways to the right or left of the object, with their head axis positioned approximately 40° adjacent to the object. This movement is believed to be associated with lining up the incoming image to fall on the deep fovea. Raptors will choose which head position to use depending on the distance to the object. At distances as close as 8m, they used primarily binocular vision. At distances greater than 21m, they spent more time using monocular vision. At distances greater than 40m, they spent 80% or more time using their monocular vision. This suggests that raptors tilt their head to rely on the highly acute deep fovea.[42]
Like all birds, raptors possess tetrachromacy, however, due to their emphasis on visual acuity, many diurnal birds of prey have little ability to see ultraviolet light as this produces chromatic aberration which decreases the clarity of vision.[43]
↑ Vieillot included the caracaras (Daptrius, Ibycter, and Polyborus) in Vulturini, though it is now known that they are related to falcons.
Related Research Articles
Falcons are birds of prey in the genus Falco, which includes about 40 species. Some small species of falcons with long, narrow wings are called hobbies, and some that hover while hunting are called kestrels. Falcons are widely distributed on all continents of the world except Antarctica, though closely related raptors did occur there in the Eocene.
A harrier is a member of the genus Circus in the a bird of prey family Accipitridae. Harriers characteristically hunt by flying low over open ground, feeding on small mammals, reptiles, or birds. The young of the species are sometimes referred to as ring-tail harriers. They are distinctive with long wings, a long narrow tail, the slow and low flight over grasslands and skull peculiarities. The harriers are thought to have diversified with the expansion of grasslands and the emergence of C4 grasses about 6 to 8 million years ago during the Late Miocene and Pliocene.
The Accipitridae is one of the four families within the order Accipitriformes, and is a family of small to large birds of prey with strongly hooked bills and variable morphology based on diet. They feed on a range of prey items from insects to medium-sized mammals, with a number feeding on carrion and a few feeding on fruit. The Accipitridae have a cosmopolitan distribution, being found on all the world's continents and a number of oceanic island groups. Some species are migratory. The family contains 256 species which are divided into 12 subfamilies and 75 genera.
Cathartidae, known commonly as New World vultures or condors, are a family of birds of prey consisting of seven extant species in five genera. It includes five extant vultures and two extant condors found in the Americas. They are known as "New World" vultures to distinguish them from Old World vultures, with which the Cathartidae does not form a single clade despite the two being similar in appearance and behavior as a result of convergent evolution.
The turkey vulture is the most widespread of the New World vultures. One of three species in the genus Cathartes of the family Cathartidae, the turkey vulture ranges from southern Canada to the southernmost tip of South America. It inhabits a variety of open and semi-open areas, including subtropical forests, shrublands, pastures, and deserts.
The Accipitriformes are an order of birds that includes most of the diurnal birds of prey, including hawks, eagles, vultures, and kites, but not falcons.
Accipiter is a genus of birds of prey in the family Accipitridae. Most species are called sparrowhawks, but there are many sparrowhawks in other genera too, such as Tachyspiza.
The Buteoninae are a subfamily of birds of prey which consists of medium to large, broad-winged species.
Circaetinae is a subfamily of the family Accipitridae which contains a group of medium to large broad-winged birds of prey. The group is sometimes treated as tribe Circaetini. These birds mainly specialise in feeding on snakes and other reptiles, which is the reason most are referred to as "snake-eagles" or "serpent-eagles". The exceptions are the bateleur, a more generalised hunter, and the Philippine eagle, which preys on mammals and birds.
The Accipitrinae are the subfamily of the Accipitridae often known as the "true" hawks. The subfamily contains 73 species that are divided into 11 genera. It includes the genus Accipiter which formerly included many more species. The large genus was found to be non-monophyletic and was split into several new or resurrected genera. The birds in this subfamily are primarily woodland birds that hunt by sudden dashes from a concealed perch, with long tails, broad wings and high visual acuity facilitating this lifestyle.
The raptor subfamily Perninae includes a number of medium-sized broad-winged species. These are birds of warmer climates, although the Pernis species have a more extensive range.
Milvus is a genus of medium-sized birds of prey. The genus was erected by the French naturalist Bernard Germain de Lacépède in 1799 with the red kite as the type species. The name is the Latin word for the red kite.
Aquila is the genus of true eagles. The genus name is Latin for "eagle", possibly derived from aquilus, "dark in colour". It is often united with the sea eagles, buteos, and other more heavyset Accipitridae, but more recently they appear to be less distinct from the slenderer accipitrine hawks than previously believed. Eagles are not a natural group but denote essentially any bird of prey large enough to hunt sizeable vertebrate prey.
The white-eyed buzzard is a medium-sized hawk, distinct from the true buzzards in the genus Buteo, found in South Asia. Adults have a rufous tail, a distinctive white iris, and a white throat bearing a dark mesial stripe bordered. The head is brown and the median coverts of the upper wing are pale. They lack the typical carpal patches on the underside of the wings seen in true buzzards, but the entire wing lining appears dark in contrast to the flight feathers. They sit upright on perches for prolonged periods and soar on thermals in search of insect and small vertebrate prey. They are vociferous in the breeding season, and several birds may be heard calling as they soar together.
The genus Hieraaetus, sometimes known as small eagles or hawk-eagles, denotes a group of smallish eagles usually placed in the accipitrid subfamilies Buteoninae or Aquilinae.
Buteogallus is a genus of birds of prey in the family Accipitridae. All members of this genus are essentially neotropical, but the distribution of a single species extends slightly into the extreme southwestern United States. Many of the species are fond of large crustaceans and even patrol long stretches of shore or riverbank on foot where such prey abounds, but some have a rather different lifestyle. Unlike many other genera of raptor, some members are referred to as "hawks", and others as "eagles".
The order Falconiformes is represented by the extant family Falconidae and a handful of enigmatic Paleogene species. Traditionally, the other bird of prey families Cathartidae, Sagittariidae (secretarybird), Pandionidae (ospreys), Accipitridae (hawks) were classified in Falconiformes. A variety of comparative genome analyses published since 2008, however, found that falcons are part of a clade of birds called Australaves, which also includes seriemas, parrots and passerines. Within Australaves falcons are more closely related to the parrot-passerine clade than they are to the seriemas. The hawks, vultures and owls are placed in the clade Afroaves.
Cariamiformes is an order of primarily flightless birds that has existed for over 50 million years. The group includes the family Cariamidae (seriemas) and the extinct families such as Phorusrhacidae, Bathornithidae, Idiornithidae and Ameghinornithidae. Extant members (seriemas) are only known from South America, but fossils of many extinct taxa are also found in other continents including Europe and North America. Though traditionally considered a suborder within Gruiformes, both morphological and genetic studies show that it belongs to a separate group of birds, Australaves, whose other living members are Falconidae, Psittaciformes and Passeriformes.
The Harpiinae is a bird of prey subfamily which consists of large broad-winged species native to tropical forests. There are 4 genera in the subfamily, all monotypic.
Telluraves is a recently defined clade of birds defined by their arboreality. Based on most recent genetic studies, the clade unites a variety of bird groups, including the australavians as well as the afroavians. This grouping was defined in the PhyloCode by George Sangster and colleagues in 2022 as "the least inclusive crown clade containing Accipiter nisus and Passer domesticus". They appear to be the sister group of the Phaethoquornithes.
↑ Mayr, Gerald (19 April 2018). "New data on the anatomy and palaeobiology of sandcoleid mousebirds (Aves, Coliiformes) from the early Eocene of Messel". Palaeobiodiversity and Palaeoenvironments. 98 (4): 639–651. Bibcode:2018PdPe...98..639M. doi:10.1007/s12549-018-0328-1. S2CID134450324.
↑ Helbig, Andreas J.; Kocum, Annett; Seibold, Ingrid; Braun, Michael J. (April 2005). "A multi-gene phylogeny of aquiline eagles (Aves: Accipitriformes) reveals extensive paraphyly at the genus level". Molecular Phylogenetics and Evolution. 35 (1): 147–164. Bibcode:2005MolPE..35..147H. doi:10.1016/j.ympev.2004.10.003. PMID15737588.
↑ Lerner, Heather R.L.; Mindell, David P. (November 2005). "Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA". Molecular Phylogenetics and Evolution. 37 (2): 327–346. Bibcode:2005MolPE..37..327L. doi:10.1016/j.ympev.2005.04.010. PMID15925523.
↑ Griffiths, Carole S.; Barrowclough, George F.; Groth, Jeff G.; Mertz, Lisa A. (September 2007). "Phylogeny, diversity, and classification of the Accipitridae based on DNA sequences of the RAG-1 exon". Journal of Avian Biology. 38 (5): 587–602. doi:10.1111/j.2007.0908-8857.03971.x.
↑ Breman, Floris C.; Jordaens, Kurt; Sonet, Gontran; Nagy, Zoltán T.; Van Houdt, Jeroen; Louette, Michel (23 September 2012). "DNA barcoding and evolutionary relationships in Accipiter Brisson, 1760 (Aves, Falconiformes: Accipitridae) with a focus on African and Eurasian representatives". Journal of Ornithology. 154 (1): 265–287. doi:10.1007/s10336-012-0892-5. S2CID17933934.
↑ Mueller, Helmut C. (1986). "The Evolution of Reversed Sexual Dimorphism in Owls: An Empirical Analysis of Possible Selective Factors". The Wilson Bulletin. 98 (3): 387–406. JSTOR4162266.
↑ Massemin, S.; Korpimäki, Erkki; Wiehn, Jürgen (21 July 2000). "Reversed sexual size dimorphism in raptors: evaluation of the hypotheses in kestrels breeding in a temporally changing environment". Oecologia. 124 (1): 26–32. Bibcode:2000Oecol.124...26M. doi:10.1007/s004420050021. PMID28308409. S2CID8498728.
↑ Sonerud, Geir A.; Steen, Ronny; Løw, Line M.; Røed, Line T.; Skar, Kristin; Selås, Vidar; Slagsvold, Tore (17 October 2012). "Size-biased allocation of prey from male to offspring via female: family conflicts, prey selection, and evolution of sexual size dimorphism in raptors". Oecologia. 172 (1): 93–107. Bibcode:2013Oecol.172...93S. doi:10.1007/s00442-012-2491-9. PMID23073637. S2CID17489247.
↑ Jones, Washington; Rinderknecht, Andrés; Migotto, Rafael; Blanco, R. Ernesto (2013). "Body Mass Estimations and Paleobiological Inferences on a New Species of Large Caracara (Aves, Falconidae) from the Late Pleistocene of Uruguay". Journal of Paleontology. 87 (1): 151–158. Bibcode:2013JPal...87..151J. doi:10.1666/12-026R.1. JSTOR23353814. S2CID83648963.
Brown, Leslie (2013). British birds of prey: a study of Britain's 24 diurnal raptors. Hammersmith, London: HarperCollins Publishers. ISBN9780007406487.
Dunne, Pete; Karlson, Kevin (2017). Birds of Prey Hawks, Eagles, Falcons, and Vultures of North America. Houghton Mifflin Harcourt. ISBN9780544018440. OCLC953709935.
Macdonald Lockhart, James (2017). Raptor: a journey through birds. Chicago: The University of Chicago Press. ISBN9780226470580. OCLC959200538.
Newman, Kenneth (1999). Kenneth Newman's birds of prey of southern Africa: rulers of the skies: an identification guide to 67 species of southern African raptors. Knysna, South Africa: Korck Pub. ISBN978-0620245364. OCLC54470834.
Olsen, Jerry 2014, Australian High Country raptors, CSIRO Publishing, Melbourne, ISBN9780643109162.
Remsen, J. V. Jr., C. D. Cadena, A. Jaramillo, M. Nores, J. F. Pacheco, M. B. Robbins, T. S. Schulenberg, F. G. Stiles, D. F. Stotz, and K. J. Zimmer. [Version 2007-04-05.] A classification of the bird species of South America. American Ornithologists' Union. Accessed 2007-04-10.
Yamazaki, Toru (2012). Field guide to Raptors of Asia. London: Asian Raptor research and Conservation Network. ISBN9786021963531. OCLC857105968.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
