Systematics and biogeography

Abstract Of the approximately nine thousand to ten thousand extant birds, some 40% constitute the evolutionarily more primitive, and typically larger bodied, non-passerines and 60% the typically smaller, and evolutionarily more advanced, passerines or ‘perching’ birds. Bowerbirds are medium sized members of the passerines, which have characters of their legs, feet, palate, syrinx, and sperm that together define them as such but none of which is unique to them (but see below). Passerines are subdivided into a more primitive group, the Tyranni or suboscines (having a mesomyodian syrinx worked by a pair of intrinsic syringeal muscles or none), and a more advanced group, known as the Passeri or oscines, with an acromyodian syrinx worked by three or four pairs of intrinsic syringeal muscles (Raikow 1982; Schodde and Mason 1999). This dichotomy of the passerines is thus based in large part upon the physical construction of the avian syrinx, which accounts for the more advanced oscines being known as the ‘songbirds’. Contemporary consensus is that the bowerbirds represent a basal, or primitive, group within the oscine passerines.