Head of moderate size, broad, rather flattened above; neck very short; body very slender, remarkably attenuated behind. Legs long and very slender; tarsus rather long, extremely slender, compressed, anteriorly covered with fifteen scutella disposed in a longitudinal plate, of which the inner sharp edge projects considerably, whence the name of “Sharp-shinned” given to this species, the sides with hexagonal scales, the hind part with numerous scutella. Toes slender, the third and fourth connected at the base by a web, extending beyond the second joint of the latter, and curving forward as far as that of the former; first and second toes strongest and about equal; third extremely elongated, fourth very slender; tuberculate and papillate beneath, there being a long fleshy tubercle on the last joint of each toe, and one on the next joint of the two outer. Claws very long, arched, gradually attenuated to a fine point.
Plumage full, soft, blended, somewhat distinct on the upper parts. Wings of moderate length, reaching beyond the middle of the tail; the fourth quill longest, the fifth scarcely shorter, the third intermediate between the fifth and seventh, the second a little longer than the seventh, the first generally shorter than the outer secondary; the first five quills cut out on the outer, the first four more deeply on the inner edge. The tail is long, even, of twelve rather broad, rounded feathers.
The bill is light blue at the base, bluish-black at the end; the cere and eyelids yellowish-green; the iris bright reddish-orange; the tarsi and toes yellow; the claws black, pale bluish at the base. The general colour of the plumage on the upper parts is deep greyish-blue, or dark slate-blue, the shafts darker; the feathers on the occiput are white at the base, that colour appearing more or less as they are raised; and on each of the scapulars are two large white patches, which, however, are not seen until the feathers are raised. The outer primaries are tinged with brown; all the quills are marked on the inner web with dusky bands, between which the inner margins are white toward the base. The tail has four broad bands of blackish-brown, and is tipped with greyish-white. The cheeks are yellowish-red, and the forehead is tinged with the same colour. The throat is reddish-white; the lower parts are transversely and rather broadly barred with light red and white, there being from three to five bars or double spots of the latter colour on each feather, those on the sides with the inner web entirely red; part of abdomen and lower tail-coverts white; feathers of the legs barred like the breast; lower wing-coverts yellowish-white, barred and spotted with dusky.
Length to end of tail 11 1/4 inches; to end of wings 8 3/4; to end of claws 11 1/4; extent of wings 20 1/2; wing from flexure 6 10/12; tail 5 10/12; bill along the ridge 8/12, along the edge of lower mandible 8/12; tarsus 1 11/12; hind toe 5 3/4/12, its claw, 6/12; middle toe 1 2/12, its claw 4 1/2/12. Weight 3 1/2 oz.
Adult Female. Plate CCCLXXIV. Fig. 2.
The female, which greatly exceeds the male in size is generally greyish-brown tinged with blue on the upper parts, in very old individuals bluish-grey or dark bluish-grey, more or less tinged with brown. The bill, cere, iris, feet, and claws are as in the male, and the markings on the plumage are similar on the upper parts; the lower are generally of a lighter tint, but otherwise nearly the same.
Length to end of tail 14 inches; extent of wings 26; wing from flexure 8 2/12; tail 6 8/12; bill along the ridge 10/12; tarsus 2 1/12; hind toe 7 1/2/12, its claw 7 1/2/12; middle toe 1 11/12, its claw 6/12. Weight of an individual 7 1/2 oz., of another 8 1/4.
Young birds of either sex, when fully fledged, have the upper parts generally hair-brown, on the back darker; the feathers on the head and hind neck margined with light red; those of the rest of the upper parts also terminally edged with brownish-red; the feathers of the hind head and neck are white at the base, but to less extent, and the scapulars are also spotted with the same. The lower parts are white or yellowish-white, the throat longitudinally streaked, the rest banded with dark brown, the feathers of the sides spotted, those of the legs light reddish, obscurely marked with darker along the middle; the lower tail-coverts white. The female has the markings on the lower parts much narrower at this age.
A male bird preserved in spirits presents the following characters:—The roof of the mouth is flat, with two longitudinal ridges; the posterior aperture of the nares oblong, with a linear anterior slit, papillate on the edges. The tongue is 5 twelfths long, narrow, concave above, slightly emarginate. The œsophagus, a b c d e, is 3 inches 3 twelfths long; its diameter at the upper part 5 twelfths; it enlarges on the neck to a capacious crop, c d, 1 inch in diameter. The proventriculus, e, has a complete belt of small oblong glandules. The stomach, f g, is large, roundish, membranous, without distinct muscles, 1 inch 3 twelfths long, and 1 inch broad. The intestine, g h i l, is 14 3/4 inches long, its greatest diameter 2 twelfths. The rectum, j l, is 1 inch 9 twelfths long; its diameter at the anterior part 3 twelfths; the cœca, j, are exceedingly small, forming two scarcely observable sacs, about half a twelfth in depth. The trachea is 2 1/12 inches long, its rings unossified, 78 in number; the bronchi long and slender, of about 18 half rings. The contents of the crop and stomach were portions of two small birds.