The diurnal Birds of Prey, if only Indian genera are taken into consideration, form a very natural and well-marked group, about which the only doubt that can arise is whether the Osprey is entitled to higher rank than that of forming a distinct family. The difficult questions as to the relationship of the American Vultures or Condors (Cathartidae) and of the African Secretary Bird (Serpentarius) do not concern us, and the Owls have now by general consent been placed in a distinct order.
In the Accipitres the bill is strong, the upper mandible considerably longer than the lower, with the culmen much curved, so that the end is hooked and the tip perpendicular; the basal portion is covered with a membrane or cere, in which the nostrils are pierced. The feet are strong and furnished with powerful claws. A hallux is always present, and there is a tufted oil-gland. The spinal feather-tract is well-defined on the neck. There are always 11 primaries. The flexor longus hallucis leads to the hallux and the flexor perforans digitorum to the other three digits, but the two tendons are united by a fibrous vinculum. The ambiens muscle and the femoro-caudal are present, the accessory femoro-caudal, semitendinosus, and accessory semitendinosus are absent. The posterior border of the sternum is not notched, but there is sometimes a foramen on each side within the border. There are no basipterygoid processes, and the palate is desmognathous. Both carotids are present, and there are caeca of the intestine. The nest is generally of sticks, and is placed on a tree or on rocks. The young are hatched helpless and covered with down; they remain in the nest for a considerable time. The female throughout the order is almost always larger than the male.
Accipitrine birds may be thus divided into three families :—
a. No aftershaft to contour-feathers; outer toe reversible ………………………Pandionidae, p. 313.
b. An aftershaft present; outer toe not or very slightly reversible.
a1. Crown of head naked or covered with down ………………………Vulturidae, p. 315.
b1. Crown of head feathered ………………………Falconidae, p. 327.