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 (except Antarctica) 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.
Many well-known birds of prey such as buzzard, eagles, harriers, hawks, kites, and Old World vultures are included in this group. The osprey is usually placed in a separate family (Pandionidae), as is the secretary bird (Sagittariidae); the New World vultures are also usually now regarded as a separate family (Cathartidae) or order. Karyotype data indicate the accipitrids analysed are indeed a distinct monophyletic group.
Systematics and phylogeny In the past the accipitrids have been variously divided into some five to ten subfamilies. Most share a very similar morphology, but many of these groups contain taxa that are more aberrant. These were placed in their respective position more for lack of better evidence than anything else. The phylogenetic layout of the accipitrids was historically a matter of dispute. Molecular studies have removed the phylogenetic uncertainty for most of the species.
The accipitrids are recognizable by a peculiar rearrangement of their chromosomes. Apart from this, morphology and mtDNA cytochrome b sequence data give a confusing picture of these birds' inter-relationships. The hawks, kites, eagles and Old World vultures as presently assigned in all likelihood do not form monophyletic groups.
The genus level cladogram of the Accipiridae shown below is based on a densely sampled molecular phylogenetic study of the Accipitridae by Therese Catanach and collaborators that was published in 2024. The number of species in each genus is based on the list maintained by Frank Gill, Pamela C. Rasmussen and David Donsker on behalf of the International Ornithological Committee (IOC).
Taxonomy The family contains 255 species that are divided in 12 subfamilies and 75 genera.
Fossil record
As with most other birds of prey, the fossil record of this group is fairly complete from the latter Eocene onwards (c.35 mya), with modern genera being well documented since the Early Oligocene, or around 30 mya. Milvoides (Late Eocene of England) Aquilavus (Late Eocene/Early Oligocene – Early Miocene of France) Palaeocircus (Late Eocene/Early Oligocene of France) Aviraptor (Early Oligocene of Poland) Palaeastur (Agate Fossil Beds, Early Miocene of Sioux County, US) Pengana (Early Miocene of Riversleigh, Australia) Promilio (Agate Fossil Beds Early Miocene of Sioux County, US) Proictinia (Early – Late Miocene/Early Pliocene of C and SE US) Neophrontops (Early/Middle Miocene – Late Pleistocene) – formerly in Neophron Mioaegypius (Xiacaowan Middle Miocene of Sihong, China) Mioaetus (Miocene of Germany) Apatosagittarius (Late Miocene of Nebraska, US) Gansugyps (Liushu Late Miocene of China) Palaeoborus (Miocene) Qiluornis (Miocene of Shandong, China) Garganoaetus (Early Pliocene of Gargano Peninsula, Italy) Dynatoaetus (Pliocene – Pleistocene of South Australia, Australia) Amplibuteo (Late Pliocene of Peru – Late Pleistocene of southern North America and Cuba) – may belong to extant genus Harpyhaliaetus Neogyps Palaeohierax – includes "Aquila" gervaisii
Accipitrids are known since Early Eocene times, or about from 50 mya onwards, but these early remains are too fragmentary and/or basal to properly assign a place in the phylogeny. Likewise, molecular methods are of limited value in determining evolutionary relationships of and within the accipitrids. The group may have originated on either side of the Atlantic, which during that time was only 60–80% its present width. As evidenced by fossils like Pengana, some 25 mya, accipitrids in all likelihood rapidly acquired a global distribution, initially probably extending even to Antarctica.
Accipitridae gen. et sp. indet. (Huerfano Early Eocene of Huerfano County, US) Accipitridae gen. et sp. indet. (Borgloon Early Oligocene of Hoogbutsel, Belgium) Accipitridae gen. et sp. indet. (Bathans Early/Middle Miocene of Otago, New Zealand) Accipitridae gen. et sp. indet. MPEF-PV-2523 (Puerto Madryn Late Miocene of Estancia La Pastosa, Argentina) "Aquila" danana (Snake Creek Late Miocene/Early Pliocene of Loup Fork, US) – formerly also Geranoaetus or Buteo Accipitridae gen. et sp. indet. (Early/Middle Pliocene of Kern County, US) – Parabuteo? Accipitridae gen. et sp. indet. (Late Pliocene/Early Pleistocene of Ibiza, Mediterranean) – Buteo? Accipitridae gen. et sp. indet. (Egypt)
Specimen AMNH FR 2941, a left coracoid from the Late Eocene Irdin Manha Formation of Chimney Butte (Inner Mongolia), was initially assessed as a basal mid-sized buteonine; it is today considered to be more likely to belong in the Gruiformes genus Eogrus. The Early Oligocene genus Cruschedula was formerly thought to belong to Spheniscidae, however reexamination of the holotype in 1943 resulted in the genus being placed in Accipitridae. Further examination in 1980 resulted in placement as Aves incertae sedis.
Morphology
The Accipitridae are a diverse family with a great deal of variation in size and shape. They range in size from the tiny pearl kite (Gampsonyx swainsonii) and little sparrowhawk (Accipiter minullus), both of which are 23 cm (9 in) in length and weigh about 85 g (3 oz), to the cinereous vulture (Aegypius monachus), which measures up to 120 cm (47 in) and weighs up to 14 kg (31 lbs). Wingspan can vary from in the little sparrowhawk to more than in the cinereous and Himalayan vultures (Gyps himalayensis). In these extreme species, wing chord length can range from and culmen length from . Until the 14th century, even these huge vultures were surpassed by the extinct Haast's eagle (Hieraaetus moorei) of New Zealand, which is estimated to have measured up to 140 cm (55 in) and to have weighed in the largest females.Worthy, T. & Holdaway, R., The Lost World of the Moa: Prehistoric Life of New Zealand. Indiana University Press (2003), In terms of body mass, the Accipitridae are the most diverse family of birds and may also be in terms of some aspects of linear size diversity, although lag behind the true parrots and pheasant family in length diversity. Most accipitrids exhibit sexual dimorphism in size, although, unusually for birds, it is the females that are larger than the males. This sexual difference in size is most pronounced in active species that hunt birds, such as the Accipiter hawks, in which the size difference averages 25–50%. In a majority of species, such as generalist hunters and rodent-, reptile-, fish-, and insect-hunting specialists, the dimorphism is less, usually between a 5% to 30% size difference. In the carrion-eating Old World vultures and snail eating kites, the difference is largely non-existent, though sometimes the female may average slightly heavier.
The beaks of accipitrids are strong and hooked (sometimes very hooked, as in the hook-billed kite or snail kite). In some species, there is a notch or 'tooth' in the upper mandible. In all accipitrids, the base of the upper mandible is covered by a fleshy membrane called the cere, which is usually yellow in colour. The tarsi of different species vary by diet; those of bird-hunting species, such as sparrowhawks, are long and thin, whilst species that hunt large mammals have much thicker, stronger tarsi, and the tarsi of the snake-eagles have thick scales to protect from bites.
The plumage of the Accipitridae can be striking, but rarely utilises bright colours; most birds use combinations of white, grey, buff, brown and black. Overall they tend to be paler below, which helps them seem less conspicuous when seen from below. There is seldom sexual dimorphism in plumage, when it occurs the males are brighter or the females resemble juveniles. In many species juveniles have a distinctly different plumage. Some accipitrids mimic the plumage patterns of other hawks and eagles. Resembling a less dangerous species may fool prey; resembling a more dangerous species may reduce mobbing by other birds. Several species of accipitrid have crests used in signalling, and even species without crests can raise the feathers of the crown when alarmed or excited. In contrast most of the Old World vultures possess bare heads without feathers; this is thought to prevent soiling on the feathers and aid in thermoregulation.
The senses of the Accipitridae are adapted to hunting (or scavenging), and in particular their vision is exceptional, with some large accipitrids such as the wedge-tailed eagle and Old World vultures having over twice the visual acuity of a typical human. Large eyes with two foveae provide binocular vision and a "hawk eye" for movement and distance judging. In addition the Accipitridae have the largest pectens of any birds. The eyes are tube shaped and cannot move much in their sockets. In addition to excellent vision many species have excellent hearing, but unlike in owls sight is generally the principal sense used for hunting. Hearing may be used to locate prey hidden in vegetation, but sight is still used to catch the prey. Although they rely primarily on vision, Accipitridae do have functioning olfactory systems, which they make use of in a variety of contexts.
Diet and behavior
Accipitrids are predominantly predators and most species actively hunt for their prey. Prey is usually captured and killed in the powerful talons of the raptor and then carried off to be torn apart with a hooked bill for eating or feeding to nestlings. A majority of accipitrids are opportunistic predators that will take any prey that they can kill. However, most have a preference for a certain type of prey, which in harriers and the numerous buteonine hawks (including more than 30 species in the genus Buteo) tends towards small mammals such as rodents.
Among the raptors that mainly favor small mammals, harriers generally hunt by hovering over openings until they detect their prey and descend upon them. Due to the specificity of their hunting style, prey preferences, and habitat preferences, usually only one harrier species tends to be found per region.
Buteonine hawks usually watch for prey from a perch but most species will also readily hunt on the wing, including from a high soar. Many buteonines are amongst the most generalized feeders, often feeding on any active small animal they find, and will generally eat whatever diurnal rodent or lagomorph is most locally common. Some buteonines, however, are more specialized, such as certain species in the genus Buteogallus, which have evolved to specialize in feeding on crabs. Larger Buteogallus, namely the solitary eagles, and Geranoaetus are much larger than other buteonines and seem to have become avian apex predators of specific habitat niches—for example, savanna, cloud forest and páramo in South America—and are thus honorary "eagles".Amadon, D. (1949). "Notes on Harpyhaliaetus." The Auk 53-56.
In Accipiter hawks (the most species-rich accipitrid genus with nearly 50 extant species), prey is mainly other birds. Accipiters are in general forest- and thicket-dwelling species. Accipiter hawks usually ambush birds in dense vegetation, a dangerous hunting method that requires great agility. Many smaller tropical species of Accipiter eat nearly equal portions of insects and reptiles and amphibians as they do of birds while some of the larger species have become more generalized and may feed extensively on rodents and lagomorphs, as well as other various non-avian animals.