Accipitridae

The Accipitridae, one of the four families within the order Accipitriformes (the others being Cathartidae, Pandionidae and Sagittariidae), are a family of small to large birds 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. Many well-known birds, such as hawks, eagles, kites, harriers 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), and the New World vultures are also usually now regarded as a separate family or order. Karyotype data indicate the accipitrids analysed are indeed a distinct monophyletic group, but whether this group should be considered a family or one or several order(s) on their own is a question still to be resolved. The accipitrids have been variously divided into some five to 10 subfamilies. Most share a very similar morphology, but many of these groups contain taxa that are more aberrant. These are placed in their respective position more for lack of better evidence than anything else. It is thus not very surprising that the phylogenetic layout of the accipitrids has always been a matter of dispute. 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' interrelationships. What can be said is that the hawks, kites, eagles and Old World vultures as presently assigned in all likelihood do not form monophyletic groups: According to the molecular data, the Buteoninae are most likely poly- or paraphyletic, with the true eagles, the sea eagles, and the buteonine hawks apparently representing distinct lineages. These appear to form a group with the Milvinae, Accipitrinae and Circinae but the exact relationships between the lineages are not at all robustly resolvable with the present data. The Perninae and possibly the Elaninae are older lineages, as are the Old World vultures. The latter are fairly likely also poly- or paraphyletic, with some aberrant species like the bearded and Egyptian vultures standing apart from the naked-necked 'true' vultures. 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 39 cm (15 in) in the little sparrowhawk to more than 300 cm (120 in) in the cinereous and Himalayan vultures (Gyps himalayensis). In these extreme species, wing chord length can range from 113 to 890 mm (4.4 to 35.0 in) and culmen length from 11 to 88 mm (0.43 to 3.46 in). Until the 14th century, even these huge vultures were surpassed by the extinct Haast's eagle (Harpagornis moorei) of New Zealand, which is estimated to have measured up to 140 cm (55 in) and to have weighed 15 to 16.5 kg (33 to 36 lb) in the largest females. 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 almost non-existent. 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 grey, buff and brown. 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. They may attempt to resemble a less dangerous species to fool prey, or instead resemble a more dangerous species in order to 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.