SHARP-SHINNED HAWK. Accipiter velox (Wilson)

Field characters.—In size, between Robin and Pigeon; spread wings rounded in outline; tail narrow and nearly square-ended. (See pl. 44f). Upper surface dark bluish gray in adults, brown in immatures; under surface mixed reddish brown and white, cross-barred in adults streaked in immatures; tail barred with blackish brown above and grayish white below. Flight rapid and direct; not often seen to circle, and never to poise on beating wings. Rarely utters any kind of notes.

Occurrence.—Fairly common on west flank of the Sierras. Recorded in summer in Transition and Canadian zones, in winter only below the level of heavy snow. Frequents woods and bottom-land thickets.

Against the broad-winged soaring hawks and the sharp-winged falcons the bird lover in the Sierras holds no brief, for these birds prey chiefly on rodents and insects and only on rare occasions attack song birds. But against the long-tailed, round-winged 'bullet hawks' he must make complaint, for these species are the unremitting enemies of other birds. Of the three species of bullet hawks in the Yosemite region, the Sharp-shinned Hawk is the smallest in size and probably the most important single enemy of the smaller song birds.

By reason of its relatively short, rounded wings and long tail this hawk is able to pursue small birds into such retreats as dense trees and bushes. It is thus often to be seen dashing into or through a thicket in pursuit of some one songster it has marked down, while consternation reigns among all the feathered creatures in the vicinity.

The nature of the Sharp-shin's depredations may best be illustrated by citing a few actual instances which came under our own observation. On December 30, 1914, a hawk of this species was seen in a grove of golden oaks on the north side of Yosemite Valley, flying in and out among the branches, and causing evident panic in a scattering flock of Western Bluebirds which had gathered there to feed on the mistletoe berries. A few days later, at Snelling, a male Sharp-shin was collected which was found to weigh 117 grams. The distended gullet and contents alone weighed 15.4 grams. Upon being opened the gullet was found to be crammed with the remains of a Linnet, including both wings (which had been plucked by the hawk before being eaten), the neck, one foot, and several other parts. A Linnet weighs about 23 grams; since the hawk had eaten nearly two-thirds of the bird, it is to be seen that it had consumed at one meal a quantity of material equal to more than one-seventh of its own body weight.

The most interesting incident concerning this hawk was recorded on December 26, 1914, near an occupied dwelling on the floor of Yosemite Valley. The observer was first attracted by a noise which sounded like that made by a weasel when caught in a trap. Upon seeking the source, he discovered a female Sharp-shinned Hawk struggling with a Blue-fronted Jay, a bird of nearly two-thirds its own bulk. The hawk was shot and killed, but even then its grip on the throat of the jay was not relaxed. Only when approached closely did the jay, apparently little injured, free himself from the talons of his fallen enemy and fly away.

The Sharp-shinned Hawk may be best distinguished from its larger and otherwise almost identical relative, the Cooper Hawk, by its nearly square-ended tail. (See pl. 44). The tail of the latter species always appears more or less rounded even when but slightly spread. The Goshawk, the other bullet hawk of the region, is a giant compared with either of the other two species. As compared with the Sparrow Hawk, the male Sharp-shin is of about the same size, but shows more rounded wings, no black streaks on cheeks, and bright reddish markings are totally lacking.

Females of the Sharp-shin are about one-fourth longer and almost twice the bulk of the males of the same species. There are decided differences in coloration between the immature and the adult birds. The immatures have brown backs with narrow reddish brown feather marginings and their breasts are streaked, while the adults have dark bluish gray backs without lighter feather margins and their breasts have a cross-barred pattern of markings. There is also a difference in the color of the iris, that of the young birds being yellow, that of the adults, chrome orange.

The legs of the Sharp-shinned Hawk are very long and slender, and bare of feathers almost to the top of the tarsus, while the claws are slender and very sharp. These are all adaptations of use in grasping the feathered prey.