This species presents a very close resemblance to the E. melanopterus of Europe, and the most evident specific difference can only be detected by raising the wing, the under side of which is quite different in the two, there being in the European bird no trace whatever of the black patch so conspicuous in the American species. The primaries, also, on both webs are lighter ash, while the ash of the upper parts in general is darker than in leucurus and invades more the head above, the forehead merely approaching white. The tail is more deeply emarginated, and the proportions of the primaries are quite different, the second being much longer than the third, and the first nearly as long as the second, far exceeding the third, instead of being about equal to the fourth. In the melanopterus, too, the black borders the eye all round, extending back in a short streak from the posterior angle, instead of being restricted to the anterior region and upper eyelid, as in leucurus.
A specimen of “E. axillaris” from Australia (13,844, T. R. Peale) appears, except upon close examination, to be absolutely identical in all the minutiæ of coloration, and in the wing-formula, with E. leucurus; and differs only very slightly in the measurements of bill and feet, having these proportionally larger, as will be seen from the table. Another (32,577, H. Mactier Warfield) has the upper parts so pale as to be nearly white.
A young specimen of E. axillaris differs from that of E. leucurus as follows: the occiput, nape, and dorsal region are stained or overlaid by dull ashy-rufous, instead of dark brownish-ashy; more blackish on the head. No other differences are appreciable.
A very characteristic distinction between leucurus and axillaris is seen in the coloration of the inner webs of the secondaries: in the former, they are abruptly lighter than the outer webs, often pure white, in very striking contrast to the deep ash of the outer surface; in the latter, both webs are of about the same shade of ash, which is much paler than in the other race. Occasional specimens of leucurus occur, however, in which there is little difference in tint between the two webs.
LIST OF SPECIMENS EXAMINED.
National Museum, 10; Philadelphia Academy, 2; New York Museum, 2; Boston Society, 4; Cambridge Museum, 2; Cab. G. N. Lawrence, 2; Coll. R. Ridgway, 2. Total, 24.
| Sex. | Wing. | Tail. | Culmen. | Tarsus. | Middle Toe. | Specimens. |
|---|---|---|---|---|---|---|
| ♂ | 11.80–12.50 | 7.30–7.60 | .66–.80 | 1.30–1.50 | 1.00–1.15 | 8 |
| ♀ | 11.60–12.65 | 7.20–7.80 | .70–.72 | 1.25–1.40 | 1.10–1.20 | 8 |
Habits. The Black-shouldered Hawk is a southern, western, and South American species. On the Pacific it is found to occupy a much more northern range of locality than in the eastern States, where it is not found above South Carolina and Southern Illinois. Specimens have been taken near San Francisco in midwinter.
Several individuals of this species, precisely identical with others from the United States, were taken by Lieutenant Gilliss, in the astronomical expedition to Chile. Its range in South America does not appear to be confined, as was supposed, to the western coast, as specimens are recorded by Von Pelzeln as having been obtained by Natterer in Brazil, at Ytarare, Irisanga, and San Joaquin, on the Rio Branco, in August, February, and January. These were taken on the heights. They are also found in the countries of Mexico and Central America.