THE first order of birds to be considered is the birds of prey (Accipitres). They are all remarkable for strong and sharply-hooked bills, and most of them have sharp and powerful talons. In the Eagles and Falcons these characters are developed in the highest degree, although many modifications of their structure take place in the order—the Vultures, for instance, and other carrion-feeding birds, not having such a hooked bill as the true Falcons and Eagles, while their feet are larger and more adapted for holding their prey than for striking it down in full career, as the Falcons do. In most of the birds of prey the female is larger than the male, and is much the more powerful bird. This fact is always recognised in falconry, especially in the short-winged Hawks, such as Sparrow-Hawks or Goshawks, whose females are always preferred, as possessing the greater power for holding ground game, such as Rabbits, Hares, &c. The difference in size is not very noticeable in the Vultures, but is unmistakable in the long-legged Sparrow-Hawks, Eagles, and Falcons. The form of the breast-bone, which plays such an important part in the classification of other birds, is a character of less value in the birds of prey, as it varies to a great extent even in those species which, by their habits and general structure, are most closely allied. Another character possessed by these birds is the distinct cere, which is present in all, though much hidden by bristles in the Owls: it is a waxy covering to the base of the bill, often hard, but generally fleshy in substance.
Birds of prey are of three kinds: Hawks, Ospreys, and Owls. Under the first name is included every rapacious bird which is not an Osprey or an Owl, and, therefore, the first thing to find out is—how to tell an Owl from a Hawk. At one time it was supposed that all Owls came out by night and all Hawks by day, and so they were separated into two great divisions, which were called diurnal birds of prey[143] and nocturnal birds of prey.[144] Now, however, that the habits of birds are getting better observed, these divisions have to be abandoned as not being entirely true, for there are Owls which are quite at home in the daylight, when they hunt for their food like any other bird of prey, and at least one kind of Hawk is known, whose habit it is to feed on Bats in the evening. This is Andersson’s Pern,[145] a kind of Kite, allied to the Honey-kite of England. It is found only in the Damara Country, in South-western Africa, and in Madagascar. A far better way to distinguish Hawks from Owls is seen in the foot, as the latter have the outer toe reversible—that is to say, they can turn their outer toe backwards or forwards as they please. This is easily observed in the living birds; and any one examining a caged Owl in the Zoological Gardens will see that it sits with its toes in pairs—two in front and two behind. A Hawk cannot do this, all his toes being arranged as in a little perching bird, such as a Sparrow or a Canary, three in front and one behind. Then, again, Owls have no “after-shaft” to the feathers, a structure which most Hawks possess. The “after-shaft” is the small accessory plume, which springs from the under-side of the main feather. In some birds it is very large, in others small. It occurs on the body feathers only, and is never found in the quills or tail feathers (see p. 238). Lastly, in addition to the reversible outer toe, and the absence of an accessory plume or after-shaft, Owls may be distinguished from all other birds of prey, save one, by the proportions of their leg-bones. In the skeleton figured on p. 241 the three principal leg-bones are pointed out; and it is the length which the tarsus bears in proportion to the tibia that is here insisted on. In the Owls the tarsus is only about half the length of the tibia; this is never the case in a Hawk, in which these two bones bear different proportions the one to the other, according to the sub-family. Thus in Sparrow-Hawks and Harriers[146] the tibia and the tarsus are equal in length. In Eagles and Buzzards, Kites and true Falcons, the tibia is always much longer than the tarsus, but is never double its length, as it is in the Owls. The term “Hawk,” which has been employed throughout the foregoing sentences, is intended to apply to every bird of prey excepting the Owls, with the sole exception of the Osprey. The habits of the Osprey are noticed later on, but they may be briefly stated to be similar to those of a Sea-Eagle, its prey consisting entirely of fish, while its plumage and general appearance are also those of an Eagle, so that in many places it is popularly known as the “Fish Hawk,” or “Fishing Eagle;” but here the resemblance of the Osprey to the Eagle ends, and in its other characters it is very like an Owl. The tibia is more than double the length of the tarsus, as in the Owls; the feathers of the body have no after-shaft, as in the Owls, and the outer toe is reversible, as in the Owls. Possessing, therefore, as it does, some of the most prominent features of the Eagles, as well as some of the most striking peculiarities of the Owls, the Osprey holds an intermediate position between these two sub-orders of birds.
HEAD AND BILL OF SEA EAGLE. (After Keulemans.)
(a) bony eye-shelf; (b) cere.
The birds of prey, then, may be separated into three sub-orders:—
(a). Outer toe not reversible; tibia varying in length in proportion to the tarsus, sometimes equal to it, but never double the length of the latter; body feathers with an after-shaft or accessory plume. (American Vultures excepted.)
I. Hawks (Falcones).[147]
(b). Outer toe reversible; tibia double the length of tarsus; body feathers without an after-shaft or accessory plume; plumage compact, as in an Eagle; no facial disk.
II. Ospreys (Pandiones).[148]