IT is a fact well known that among the mammals there are certain groups the so-called carnivores — which are especially adapted for preying upon their fellows. Among the birds there are also groups the members of which are fitted in one way or another for an equally rapacious existence, inasmuch as they obtain their entire subsistence from animal life, most of which they pursue and capture alive. The most prominent of these rapacious groups of birds was formerly, and indeed may still conveniently be called, the Raptores, or Birds of Prey. It was divided into two parts, the Diurnal Birds of Prey, or those which mainly seek their food by daylight, as Eagles and Hawks, and the Nocturnal Birds of Prey, typified by the Owls, which secure most of their prey by night. This implied a more or less close relationship between the Eagles, Hawks, and allied forms, and the Owls; but investigation in recent years has settled pretty conclusively that, beyond the similarity of their adaptation for rapacious life, there is little or no real relation-ship between them. The Owls could not possibly have been derived from existing Diurnal Birds of Prey, nor even from a common ancestor, but appear to find their closest relatives among the Roller-like birds, where they are accordingly placed. Their affinities and interrelationships will be fully considered under that group.
Among the Falcon-like birds the adaptation to a raptorial mode of life has so profoundly modified the skeleton that much of the evidence concerning the origin of the group has been defaced or obscured. According to Beddard, and this is confirmed by Pycraft, both eminent anatomists, it appears that the evidence points to the derivation of this group from the Stork-like birds, not, of course, directly from the modern representatives, but at a point low down on the gruine stem, even before the characters common to the diverging branches of Storks and Cranes began to undergo transformation. It is not necessary to go further into this matter at present, but it may be stated that much remains to be done in the way of investigating the skeletal and other characters within this and neighboring groups before the final word can be said.
The Falcon-like birds are so characteristic in appearance and in general so well known, that they are hardly ever mistaken, even by the most careless observer. Typically they are birds of robust size, with powerful wings which enable them to pursue and capture other birds or swift-moving animals of various kinds. They mostly have short but very stout bills with a strongly arched tip and sharp cutting edges, thus being admirably adapted for tearing flesh, skin, or even breaking bones. They have mostly rather short, stout legs, although, as will be shown later, there are certain notable exceptions to this. The feet are also strong and provided, in most cases, with long, much curved, and very sharp claws. In those which feed on dead animal matter, however, the claws are often blunt and weak as compared with those which capture their own prey. Another distinguishing feature is the cere, which is a peculiar membrane sheathing the base of the upper mandible. The nostrils open in or through the edge of the cere, which may be either soft or horny. There are only two other important groups of birds possessing the hooked bill and the cere: namely, the Owls and the Parrots. From the former they differ in the close, harsher plumage, non-reversible fourth toe (except Pandioninae), and diurnal habits, and from the latter in the structure of the feet. Technically the Falcon-like birds have many osteological features in common with the two preceding orders, but they may always be separated from them by the raptorial feet, which are never webbed.
The present order (Falconiformes) is divided, according to Pycraft, into three suborders : the Cathartae, which embraces the American Vultures, the Gypogerani, which includes only the Secretary-Bird of Africa, and the Accipitres, under which is included all remaining forms of Falcons, Eagles, Hawks, Buzzards, Old World Vultures, etc. The latter is further subdivided into two families, the Falconidce, with two subfamilies, and the Buteonidce, embracing thirteen subfamilies. The characters on which each is founded are presented under the several headings.