Males and females have similar lengths at . Their weight can range from , with males weighing more than their female counterparts. Wingspans range from . The breeding male is unmistakable. Most of the body plumage is finely vermiculated grey, with the long sickle-shaped tertials, which give this species its name, hanging off its back. The large head is dark green with a white throat, and a dark green collar and bronzed crown. The vent region is patterned in yellow, black and white.