The Accipitridae genus of raptors contains many diverse different species of birds, some appear unrelated, but the all do have similar evolutionary ancestry.
Apart from some of the obvious groups of birds in the genus, further splitting the birds into similar groups has caused problems. Many of the birds have characteristics of different groups, however the birds are grouped. One common grouping of the birds has 6 different groups
- True Hawks
birds of the Accipiter family, including the only two British accipiters, the goshawk & sparrowhawk. These birds have short, rounded wings & a long manoeuvrable rounded tail. The tail in particular gives these birds good turning & breaking ability, making them very agile in flight, highly suited to chasing their prey through dense woodland.
- Buzzards & buzzard-like birds
this includes birds of the Buteo family (e.g. the common buzzard) & other birds sharing similar characteristics (e.g. Harris Hawk). The main characteristics of this group of birds are broad wings, longer than those of accipiters, with pronounced primaries that look like fingers in flight & a broad, rounded tail. Those two features enable the birds to search for prey by soaring on thermals, the spread primary feathers allow for very slow flight, preventing stalling. They are more suited to catching their prey in open or very lightly wooded areas, and they are much less manoeuvrable than the accipiters. In America, buzzards are often referred to as hawks, while the term buzzard is used for the New World Vultures.
this includes birds from 6 different families, True Eagles, Fish (or Sea) Eagles, Booted Eagles, Hawk Eagles, Snake Eagles & Specialist Eagles. Eagles are generally much larger than buzzards and are powerfully built, regardless of size. Similar to buzzards, they have broad rounded wings & a broad rounded tail, but they have larger feet & a much heavier beak. In flight, they are much more ponderous than buzzards & rely more on surprise to catch their prey, rather than pursuit. Many, especially the booted eagles, have fully feathered legs, all the way down to the feet, this is rarer in the fish & snake eagles.
birds of the Milvus, Elanus & Pernus families, including the Red Kite & the Honey Buzzard. Kites are very lightly built, with long narrow wings and a long narrow, often forked tail. In flight, the wings give a great deal of lift, coupled with the low body weight they have a very low wing loading, making them very buoyant in the air, consequently they are very graceful fliers. They tend to have a small, sometimes partly bare, face & small beak. They eat a large amount of carrion.
this group consists of the 13 species of the Circus family. The birds are characterised by their slender build, long tail, long legs & particularly, a facial disc, similar to an owls. Beneath the feathers of the head, they have very large ear openings, giving a highly developed sense of sound. This is not an adaptation for low-light hunting, like owls, it is for detecting their prey in long grass or rushes.
- Old World Vultures
this group consists of the 15 species of the Aegypiinae family. Whilst having some characteristics in common with New World Vultures, they have evolved from the same ancestors as the other birds in this group, unlike the New World Vultures. They have long bald necks & bald heads & large heavy beaks, similar to the New World Vultures, but their large feet are more eagle like & suited to gripping. They have a less developed sense of smell & rely more on sight to find their food, both directly & by observation of other vultures heading down towards the carcass. occasionally, they will take help live prey. In size they range from large to very large. They are found throughout the Old World, i.e. Europe, Africa & Asia.
It should be noted that the characteristics of the birds in each of the groups are only very general, in all groups there will be birds that do not possess all (or even any) of the the general characteristics of that group.
Brown & Amadon, the authors of one of the authoritative books on diurnal raptors (Eagles, Hawks & Falcons Of The World) divide the birds slightly differently, into eight groups :
- Elaninae (white-tailed kites)
- Perninae (swallow-tailed kites)
- Milvinae (True kites)
- Accipitrinae (True hawks)
- Buteoninae (True buzzards, hawks & majority of eagles)
- Aegypiinae (Old World Vultures)
- Circinae (harriers)
- Circaetinae (serpent eagles)
There is often confusion as to what is a hawk & what is an eagle, in fact it is really just a matter of the name of the bird. There is no distinct taxonomic categorisation of hawks & eagles, as can be seen from the two different sets of groupings above. In general, it could be said that the difference between the two is a matter of size, the larger birds being eagles & the smaller hawks, but even so, there is still an overlap in sizes, some of the smaller eagles are smaller than some of the larger hawks (e.g. the Red-Tailed Hawk is much larger than the smallest eagle - the Australian Little Eagle (Hieraaetus morphnoides), which often weighs around 1lb). One definition is that an eagle is any member of the accipitridae that is not a true hawk, buzzard, kite, harrier or vulture (possibly adding the proviso that it must also be relatively large).
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