The young plumage described above is the Buteo bairdi, Hoy, of authors. The melanistic plumage is B. insignatus, Cassin.
The young birds of this species are as variable as the adults; thus, No. 53,210, ♂, has the fine ochraceous of the lower parts entirely free from spots, except across the breast; on the upper parts the ochraceous spotting is so extended as to almost prevail, while another, from the same nest, has the black beneath exceeding the ochraceous, the tibiæ being thickly spotted, and the lower tail-coverts barred. Both these specimens belong to a brood of four, which were hardly able to fly, and were shot, with their parents, the male of which is the one described, while the female (No. 53,206) is a very dark example of insignatus, Cassin.
The type of bairdi, and another Wisconsin specimen, are in the collection of the Philadelphia Academy. In plumage, they are unlike any others I have seen, though there is as little resemblance between these two as between any I have compared. Dr. Hoy’s type (Racine, Wisc., January, 1854) differs from others, in exceedingly pale colors; the cream-color beneath is scarcely spotted, there being only a few triangular spots and shaft-lines of black on the sides; the lining of the wing is entirely immaculate. Above, the black is unusually continuous; the under surface of the primaries is unusually white. Wing, 15.00; tail, 8.00.
The other specimen (Menonomee Marsh, Milwaukee, Wisc., spring of 1851) is just the opposite extreme in plumage, being unusually dark, for a young bird. Beneath, the black spots are so large as to nearly cover the whole surface, while the continuity of the black of the upper part is almost unbroken. The head above, and nape, and broad “mustache” stripe from angle of mouth down to the jugulum, with nearly the whole pectoral area, unbroken black, leaving the gular region and side of the head pale, but thickly streaked. Wing, 15.00; tail, 8.80; tarsus, 2.35; middle toe, 1.50. These specimens may be said to form about the extremes of the young plumage. An Iowa skin (No. 59,052; Ricksecker) is like the average of far-western examples.
The melanistic condition bears to the normal plumage of swainsoni precisely the same relation that the black calurus, Cassin, does to the usual style of the western variety of borealis (borealis var. calurus = montanus, Cassin); the variable series, connecting these two extremes, and designated by the name borealis var. calurus, which covers the whole, finds an exact parallel in the present species.
A specimen from the Platte (5,576, ♂, August; W. S. Wood) is entirely dark rufous-brown beneath (excepting the lower tail-coverts), with the shafts of the feathers black.
This species is entirely distinct specifically from the B. vulgaris of Europe. The latter has four, instead of only three, outer primaries deeply emarginated, and is very dissimilar in every stage of plumage.
Var. oxypterus, Cassin.
SHARP-WINGED HAWK.
(Normal young plumage.)
Buteo oxypterus, Cass. P. A. N. S. VII, 1855, 282.—Ib. Birds N. Am. 1858, 30.—Strickl. Orn. Syn. I, 1855, 28.—Coues, P. A. N. S. 1866, 9.—Gray, Hand List, I, 8.—Cooper, Birds Cal. 1870, 480. Buteo albicaudatus, “Vieill.,” Sclater, P. Z. S. 1869, 634, No. 22.