The whistling ducks or tree ducks are a subfamily, Dendrocygninae of the duck, goose and swan family of birds, Anatidae. Whistling ducks are found in the tropics and subtropics. As their name implies, they have distinctive whistling calls. The whistling ducks have long legs and necks, and are very gregarious, flying to and from night-time roosts in large flocks. Both sexes have the same plumage, and all have a hunched appearance and black underwings in flight.