Basal joint of toes without transverse scutellæ; tarsus about equal to middle toe.
Coloration of the sexes in adult plumage very different in tints; in the young alike, the young ♂ resembling the adult ♀. Size small … Æsalon.
Basal joint of toes with transverse scutellæ; tarsus longer than middle toe.
Coloration of the sexes very different, in pattern and tints, at all ages; old and young alike. Scutellæ of the toes and tarsus interrupted at the digito-tarsal joint; tarsus much longer than middle toe. Bill small, the cere on top less than one fourth the culmen. Size small … Tinnunculus.
Coloration of the sexes alike at all ages; old and young slightly different in pattern and tints. Scutellæ of tarsus and toes uninterrupted from “knees” to claws; tarsus but little longer than middle toe. Bill large, the cere on top about one third the culmen. Size medium; form very slender … Rhynchofalco.
Subgenus HIEROFALCO, Cuvier.
- Hierofalco, Cuvier, 1817. (Type, Falco gyrfalco, Linn.)
- Jerafalco, Boie, 1822; Kaup, 1851. (Same type.)
- Gennaia, Kaup, 1847. (Type, Falco jugger, Gray.)
Species and Races.
1. F. gyrfalco. Wing, 13.00–17.00; tail, 8.50–11.50; culmen, .85–1.05; tarsus, 2.10–3.00; middle toe, 1.80–2.25.[45] Ground-color varying from entirely pure white to wholly dusky, but generally bluish (in adult) or grayish-brown (in young) above, and white beneath. Adult. All the markings transverse.[46] No lighter nuchal band. Young. Markings of the lower surface longitudinal, the upper parts without transverse bars (except on the tail[47]).
a. Lower parts with white predominating, or wholly white.