Genus CIRCUS Lacépède, 1799.
Bill moderate or weak, somewhat compressed; margin of upper mandible slightly sinuate but not toothed; wing very long and pointed, first primary short, about equal to sixth; secondaries much shorter than primaries; tail long, slightly graduated or nearly square; tarsus long and slender, feathered at the base and overhung for about half its length by the long thigh-feathers; front of tarsus with transverse plates, sides and most of the hinder aspect with hexagonal scales; toes long, nails long and much curved; behind ear-coverts and sometimes across the throat a “ruff” of short, rather stiff feathers, most conspicuous in the young of melanoleucos and not very evident in the other species.
The harriers or marsh hawks are noticeable among birds of prey for their slender form, long slender legs, and slow flight. Adult birds can be easily identified but the immature specimens present considerable difficulty.
Species.
(Adult.)
- a1. Upper parts black; tail silvery gray; lower breast, abdomen, and crissum white.
- a2. Upper parts dark brown; tail bluish ash. æruginosus (p. [215])
(Immature.)
- a1. Facial ruff complete across the throat; smaller, tarsus about 70 mm.; wing, 340 mm. melanoleucos (p. [214])
- a2. Facial ruff incomplete; tarsus about 90 mm.; wing, 400 mm.