General form compact and strong; bill strong, short, with a distinct and sharp tooth in the upper mandible; wings long, pointed; tail moderate, or rather long; tarsi short, robust; toes long, claws large, curved, sharp; tarsi covered with hexagonal or circular scales. A genus of birds remarkable for their courage and very rapid flight, species of which are found in all countries.
Falco polyagrus. Cassin, Birds of California and Texas, I. p. 88. (1853.)
Form robust; wings rather long, second and third quills longest, and nearly equal; tail rather long; bill short, rather wide at base; tooth in the upper mandible prominent.
Dimensions. Female. Total length of skin, about 20 inches; wing, 14; tail, 8 inches.
Colors. Female nearly adult. Narrow frontal band, line over the eye, and entire under parts white; narrow stripe from the corner of the mouth running downwards, dark brown; some feathers on the breast, and abdomen with longitudinal stripes and spots of brown, which color forms a large and conspicuous spot on the flank. Entire upper parts brown, paler on the rump, many feathers with rufous edgings; tail above pale grayish-brown, with transverse bars of white, and narrowly tipped with white; quills dark grayish-brown, with numerous bars of white On their inner-webs; under wing-coverts dark brown; edge of the wing at the shoulder and below, white, spotted with brown. The brown of the back extending somewhat on to the breast at the wing. Bill, bluish horn color, under mandible yellow at its base. Large space around the eye, bare, with a narrow edging of brown on the first plumage by which it is encircled.
Younger female. Entire plumage above and below, brownish-black; throat white; many feathers on the under parts with edgings and circular spots of white; under wing-coverts also with circular spots of white, and the under tail-coverts with wide transverse stripes of the same.
Young male? Frontal band nearly obsolete; entire upper parts uniform pale brown, with narrow rufous stripes on the head; under parts white, with a tinge of fulvous, and nearly every feather with a narrow longitudinal stripe of blackish-brown; large spaces on the flanks, brown; tarsi and feet, lead-colored.
Hab. Oregon and California. Spec. in Nat. Mus., Washington; and Mus. Acad., Philada.
Obs. This is the only American Falcon yet discovered, which belongs to the group forming the sub-genus Gennaia, Kaup., which contains Falco laniarius, Linn., (Gould, B. of Eur., I. pl 20); Falco biarmiaus, Temm., (Pl. col., 324); Falco jugger, Gray, and several other species. It especially resembles the last, but is larger, and we are at present of opinion that the young of the two species differ in the colors of their plumage.