Birds of prey, also known as raptors, hunt and feed on other animals. The term "raptor" is derived from the Latin word rapere (meaning to seize or take by force). These birds are characterized by keen vision that allows them to detect prey during flight and powerful talons and beaks.
Many species of birds may be considered partly or exclusively predatory. However, in ornithology, the term "bird of prey" applies only to birds of the families listed below. Taken literally, the term "bird of prey" has a wide meaning that includes many birds that hunt and feed on animals and also birds that eat very small insects. In ornithology, the definition for "bird of prey" has a narrower meaning: birds that have very good eyesight for finding food, strong feet for holding food, and a strong curved beak for tearing flesh. Most birds of prey also have strong curved talons for catching or killing prey. An example of this difference in definition, the narrower definition excludes storks and gulls, which can eat quite large fish, partly because these birds catch and kill prey entirely with their beaks, and similarly bird-eating skuas, fish-eating penguins, and vertebrate-eating kookaburras are excluded. Birds of prey generally prey on vertebrates, which are usually quite large relative to the size of the bird. Most also eat carrion, at least occasionally, and vultures and condors eat carrion as their main food source. Many raptor species are considered apex predators.
The order Accipitriformes is inferred to have originated ~44 million years ago when it split from the common ancestor of the secretarybird (Sagittarius serpentarius) and the rest of the accipitrid species. The phylogeny of Accipitriformes is complex and difficult to unravel. Widespread paraphylies were observed in many phylogenetic studies. Unfortunately more recent and detailed studies are shown similar results. 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).
The diurnal birds of prey are formally classified into five families of two orders.
These families were traditionally grouped together in a single order Falconiformes, however are now split into two orders: Falconiformes and Accipitriformes. The Cathartidae are sometimes placed separately in an enlarged stork family (Ciconiiformes), and may be raised to an order of their own (Cathartiiformes).
The secretary bird and/or osprey are sometimes listed as subfamilies of Acciptridae: Sagittariinae and Pandioninae respectively.
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 Turnton.
Louis Pierre Veillot 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.
Thus Veillot'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), Veillot 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).
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.
Variations in shape and size
Eagles tend to be large birds with long, broad wings and massive feet. Booted eagles have legs and feet feathered to the toes and build very large stick nests.
Ospreys, a single species found worldwide that specializes in catching fish and builds large stick nests.
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 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).
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.
Falcons are medium-size birds of prey with long pointy wings. Unlike most other raptors, they belong to the Falconidae, rather than the Accipitridae. Many are particularly swift flyers. 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 the Buteos or the vulturine birds, or both.
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.
Migratory behaviour evolved multiple times within accipitrid raptors. The earliest event has occurred nearly 14-12 million years ago. This result seems to be one of the oldest dates published so far in the case of birds of prey. For example a previous reconstruction of migratory behaviour in one Buteo clade with a result of the origin of migration around 5 million years ago was also supported by that study.
Other interesting fact that migratory species of raptors had a southern origin because it seems that all of the major lineages within Accipitridae had an origin to one of the biogeographic realms of the Southern Hemisphere. The appearance of migratory behaviour was occurred in the tropics parallel with the range expansion of migratory species to temperate habitats. Similar results of southern origin in other taxonomic groups can be found in the literature.
It can be said that 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, but its relevance needs further investigations. The evolution of migration in animals seems to be a complex and difficult field with many unanswered questions.
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.
Olsen, Jerry 2014, Australian High Country Raptors, CSIRO Publishing, Melbourne, ISBN 9780643109162.