The long-winged hawk is known by the following characteristics:--The second primary feather in the wing, reckoning from the outside, is the longest, or at least equal in length to any other, as in the merlin, which has the second and third feathers very nearly or quite of the same length. The upper mandible has on each of its sides, about a third part of the distance from the point to the cere, a projection somewhat resembling a very blunt tooth. The eye is dark brown. The wing is long enough in the outer joint to come down, when closed, considerably more than half-way between the end of the tail coverts and the end of the tail itself, and in some cases, as in the hobby, as far as the tail, or even farther. In the short-winged hawks the wing is comparatively short in the outer joint, and, when expanded, presents a rounded appearance at the end, the fourth primary being the longest, and the first very short. That emargination, or narrowing in, of the feather near its end, which is observable in the first two primaries of the long-winged hawk, is still more pronounced in the short-winged, and is conspicuous in the third and fourth primaries also. The tail is long, and large when expanded. The iris is of some shade of yellow, light or dark. The upper mandible curves in a smooth line, without any projecting tooth. [Illustration: WING of LONG-WINGED HAWK WING of SHORT-WINGED HAWK WING of EAGLE SHAPE OF WINGS] In the eagles the tail is shorter and stouter. The outer joint of the wing is shorter than in the falcons, the wing deriving its power from the feathers near the body rather than from the outer ones. The beak is longer in shape than that of the other two sorts, and the legs are proportionately stouter. The size of the smallest eagle is very much greater than that of the largest falcon or hawk. The differences which exist in the shape of the wing between the three classes will perhaps be best appreciated by a glance at the accompanying illustration, in which a characteristic wing of each kind is figured.