Distinguishing Characteristics

Medium-sized raptor. Overall length and mass of live adults: males 360–390 mm, 360–440 g; females 370–395 mm, 350–570 g (REB). Sexes strikingly dimorphic in plumage, less so in size; females in general slightly larger than males (Friedmann 1950). Bill relatively narrow in width and depth, strongly down-curved, culmen concave throughout, and tip coming to sharp point. Cere broad and straight across top of upper mandible and angled rearward laterally. Nostrils near anterior edge of cere; small, horizontal, and elliptical. Lores and rictal area almost bare with small black bristles; all more pronounced in adults. Ten primaries; P7 and P8 are longest. P7–10 (outermost 4) have inner webs sinuated. Wings long, broad, and paddle-like in shape with a slight crook at wrist; in flight held bowed downward or cupped. Wingspread from specimens 104–112 cm (Clark and Wheeler 1987, W. S. Clark pers. comm.). Wing-tips extend 2–4 cm beyond tail when perched, a feature not apparent in most museum skins. Upper part of tarsus feathered; lower, unfeathered portion small in diameter for a raptor. Toes long and slender with long, slender, curved claws which are quite acute. Middle claw pectinate along proximal side. Tail square-cornered and slightly emarginate across tip. Rectrices total 12.

In Definitive Basic plumage, adult male slate colored with head darker, remiges slaty black, tail black with basal third white, and tail-coverts white. Narrow terminal band of rectrices off-white to gray. Adult female in same plumage dark brown dorsally and white to buffy ventrally with varying amounts of dark brown streaking on breast and belly. Fine white streaking on forehead and often on crown, and white chin and throat. Most adult females have white superciliary and cheek and dark brown eye-line. Latter features may be lacking in older females as head and neck are slaty brown and similar to male except for white chin and throat. Tail similar to male. Predefinitive plumages similar to adult female except for more cinnamon-buff or tan tones on underparts. Definitive Basic plumage color and pattern are consistent throughout species’ range (Friedmann 1950, Amadon 1975, Beissinger 1988). No albinistic, leucistic, or melanistic specimens known. Can be confused with Northern Harrier (Circus cyaneus), but latter has white uppertail-coverts, longer and narrower tail, longer and narrower wings held in pronounced dihedral, and generally flies in more direct line rather than in slower, buoyant, floppy manner of Snail Kite.