Passerines are birds of the order Passeriformes. These birds known as perching birds are divided into three orders: Passeri, Tyranni, and Acanthisitti. The Passeri contains the oscines, which are collectively known as song birds. Tyranni contains the suboscines, which are thought to be more primitive species than the Passeri. The vocalizations of these birds will sound more mechanical. The Acanthisitti is believed to be an ancient third group containing only the New Zealand wrens. Combined these three groups include over 6000 bird species.