On comparing several specimens, male and female, of this Sharp-shinned Hawk, with others of the European Sparrow Hawk, the proportions are found to be similar, as are the colours of the upper parts; but the American birds, especially the males, are much smaller; and the transverse bands on the lower parts of the Sharp-shinned Hawk are redder and broader than those of the Sparrow Hawk. The number of dark bands on the tail is the same in both, namely four on the middle feathers, and six on the lateral. The tail is not always precisely even, being in both European and American birds often slightly rounded, the lateral feather being sometimes a quarter of an inch shorter than the longest.
A species most intimately allied to the Sharp-shinned Hawk presents the same form and colours, but differs somewhat in its proportions, and is much larger. The bill is much higher at the base, its upper outline slopes from the commencement, and the festoon on its edge is less prominent. The tarsi and toes are proportionally stronger, the edge on the former not nearly so prominent. The first quill is a little longer than the first secondary, the fifth quill (not the fourth) is longest; and the tail is rounded, the lateral feather in a female being eight-twelfths of an inch shorter than the longest. The dimensions of a female of this species, shot by myself in South Carolina, are as follows:—
Length to end of tail 16 1/2 inches; wing from flexure 10; tail 7 10/12; bill along the ridge 1; tarsus 2 7/12; hind toe 10/12, its claw 1; middle toe 1 8/12, its claw 7 1/2/12.
It is very probable that this is the Accipiter Mexicanus of Mr Swainson, whose brief account of a female of that species, in the Fauna Boreali-Americana, agrees sufficiently with it. There are, however, some errors in his critical observations, at p. 44. Thus, he states that Wilson’s figure of the Slate-coloured Hawk, Accipiter Pennsylvanicus, is perfectly characteristic, in having the tail quite even at the end; but that Temminck’s Autour a bec sinueux is doubtful, the tail being represented as distinctly rounded. Now, in fact, the tail of our Sharp-shinned Hawk is when perfect a little rounded, but often when worn quite even or square. Both the figures in Plate CCCLXXIV represent it as a little rounded, and such it is in five specimens out of eight, four of these being females, and one a male; while the three specimens in which the tail may be said to be quite even are males. Again, he states that “the anterior scales on the tarsus of A. Pennsylvanicus are entire, being apparently formed externally of one entire piece; whereas in Mexicanus, the transverse divisions are distinctly visible.” The latter part of the sentence is certainly correct, in so far as may be judged from a single very fine specimen; but the scales are equally distinct in all the younger individuals of the A. Pennsylvanicus, although in one, an old male, the distinctions between the greater number are obliterated, so that they resemble a single plate. There is nothing very remarkable in this, however, for the like happens to other Hawks; it having been long ago remarked with regard to the Sparrow Hawk of Europe, Accipiter Nisus, that “in some individuals, the anterior oblique scutella, as well as the hexagonal scales of the sides, are so indistinct, that all traces of them disappear when the parts become dry.”
Accipiter Nisus, A. velox, and A. Mexicanus, which are most closely allied, insomuch that it is extremely difficult to distinguish them from each other, may be characterized as follows:—
A. Mexicanus is largest; has the fifth quill longest, the first primary much longer than the last, the tail distinctly rounded, the tarsi stouter, and with fifteen scales; the upper parts deep slate-blue; the lower banded with light red and white.
A. velox is smallest, has the fourth quill longest, the first primary much shorter than the last, the tail even, the tarsi extremely slender, with fifteen scales; the colours exactly as in Mexicanus.
A. Nisus is intermediate in size, never so small as velox, but sometimes as large as Mexicanus, with the fourth quill longest, the first and last primary about equal, the tail very slightly rounded or even, the tarsi very slender, with eighteen scales, the upper parts deep slate-blue, the lower narrowly banded with light red in the male, and dusky in the female.
This species was described by Wilson under the name of Sharp-shinned Hawk, Falco velox, and figured in Pl. XLV, a young female only being represented, although a description is given of a young male also. He afterwards figured an adult male (Pl. XLVI), and described it under the name of Slate-coloured Hawk, Falco Pennsylvanicus, considering it as a distinct species. It appears, however, that it had previously been described under several names. Thus Falco fuscus of Miller and Gmelin, and the American Brown Hawk of Latham, seem to be the same bird in the young state. Falco dubius of Gmelin and Latham, the Dubious Falcon of the latter and of Pennant are also synonymous. The Dusky Falcon of Pennant and Latham, Falco obscurus of the latter and of Gmelin, may also belong to the same species. If we consider priority of name as of paramount importance, then, in so far as can be shewn, the species ought to be named the “American Brown Hawk, Falco fuscus;” or, according to the newer nomenclature, Astur or Accipiter fuscus. The names of “Sharp-shinned,” “Slate-coloured,” and “velox” are not more distinctive; and Pennsylvanicus is out of the question, having been applied to another species.