The ou is a heavy-bodied Hawaiian honeycreeper endemic to the islands of Hawaii and Kauai. It is approximately 15.5 to 17.5 centimeters (7 inches) in total length. The upper parts are dark olive-green, and the under parts are a lighter olive-green grading to whitish on the undertail coverts. The wings and tail are a darker brownish olive. Ou are sexually dichromatic, males having a bright yellow head that contrasts sharply with the back and breast, and females having an olive-green head similar in color to the back. Juveniles are similar to the female in color but somewhat darker. In both sexes the bill is pale pink to straw-colored, with a hooked, parrot-like upper mandible. The legs are pinkish (Munro 1960, Berger 1981, Pratt et al. 1987). Males are slightly larger than females.