The Réunion harrier is the only raptor currently breeding on Réunion Island and has the smallest population of any bird species there. The male Réunion harrier has a predominantly black head and dark back, contrasting with light grey primaries and secondaries, and a white rump, belly and underwings. Female Réunion harriers are larger than males and have dark brown plumage with a barred tail. Immature Réunion harriers are similar in appearance to the female birds, while chicks are pale grey. This species has relatively short, rounded wings, which are thought to be an adaptation to hunting in dense vegetation, and a long middle toe which is typical of a bird-hunting specialist. The Réunion harrier can be heard making a grating kiay-kioo near the breeding site, and the male calls with a kai pi-pi-pi-pi-pi during display flights.