The snail kite is an accipiter of dark grey plumage and medium size. Females and juveniles are generally browner in color. It is the only species in its genus and is easily recognized by its orange ceres and legs. Also, the snail kite has a distinct sharply hooked black bill that is useful in handling apple snails. Wings are large and have a barred gray pattern below, while the tail ends in a square shape with white underside. The rump is also white and the eyes of both male and female adults are red.
The only species that resembles the Snail Kite in its range is the Slender-billed Kite (Helicolestes hamatus) because it is morphologically similar and also shares an obligate snail-eating behavior. They differ in that the Slender-billed Kite exhibits an entirely dark and shorter tail. At closer distances, H. hamatus may be identified for its yellow eyes while R. sociabilis has maroon eyes. Black Hawk species, like the Common Black Hawk (Buteogallus anthracinus), exhibit similar coloration, but have larger wings and shorter tails, and prefer habitats different from those the Snail Kite inhabits. Northern Harriers (Circus cyaneus) can resemble female and immature Snail Kites, but fly with wings at a dihedral, are more brown in coloration, and exhibit an owl-like facial disk. Other species do not exhibit as much black in the plumage and do not share the Snail Kites habitat and behavior (Ridgely et al., 1989).
The Snail Kite is a medium sized raptor that is distinctive for its sharply hooked and slender bill and red to orange ceres and legs in the adult male, while the legs and feet of females and juveniles range from an orange to a yellow color (Sykes et al., 1995). Plumage is mostly grey and males have a darker coloration while females are browner above. The basal first half of the square-tipped tail underparts are white, as are the tail coverts and the rump. The underparts of the wings have a light gray and darker gray barred pattern (Ridgley et al., 1989). Juveniles differ from females only in that they are streaked brown more heavily in the cream chest (Ridgley et al., 1989) and eye color in both adult sexes is red while in juveniles the eyes are brown (Clark et al., 1987).
Some Snail Kites exhibit stepwise wing molt as they lose individual flight feathers that are replaced before the adjacent one is dropped. Little is published on the molt patterns of Snail Kites, but it seems that they typically follow similar patterns to other large, long-winged raptor species. The females start to molt inner primaries at the beginning of the breeding season, and males after the first chicks hatch (Howell, 2010).
Iris: in both female and male adults it is red, for juveniles the color is brown (Clark et al., 1987)
Bill: color is black and shape is decurved and very slender, thought of as specialized for eating apple snail prey (Ridgley et al., 1989).
Tarsi and toes: raptorial feet are orange to red in males or orange to yellow in females and juveniles (Sykes et al., 1995).
Relative to other Snail Kite subspecies, R. s. sociabilis specimens have large wings and medium sized bills. In Honduras, wing chord measurements vary from 325-350 to 350-360 mm and exposed culmen measurements from 24-26.5 to 28.1-29.9 mm. However, R. s. major is bigger, for it has wing chord measurements of 365-382 mm and the chord of culmen measures 29.5-33 mm. R. s. plumbeus is also a relatively large race, although the bill is measured to be about the same size as those of R. s. sociabilis, smaller than those of R. s. major (Freidmann, 1933; Monroe, 1968; Amadon, 1975). Full body length is 36-39.5 cm and the wingspan is 109-116 cm (Sykes et al., 1995).