The present study investigated the effects of island isolation on songs of three species of Australian songbirds. The characteristics of songs recorded from mainland locations were compared with those recorded on Rottnest Island off the coast of Western Australia. In all three species, the characteristics of the island song patterns differed from those on the mainland. Each species exhibited a different kind of divergence on the island, including (1) differences in the structure of individual notes and syllables constituting songs; (2) differences in temporal patterns of song delivery; and (3) differences in the order of notes within songs. In two species, the island songs were less complex than mainland songs and this may be the consequence of a founder effect. In the third species, island songs were more elaborate and diverse, and this may be the consequence of sexual selection, although other explanations are plausible. For several of these populations, quantitative comparisons were made between samples collected 6-7 years apart. In two species, new recordings made in 2004 were compared with those made in 1998 and, in one species, recordings made in 1991 were compared with those made in 1998. For the nine comparisons available, similarity scores across years did not change significantly; thus, there was no evidence of systematic divergence with time.

Cultural innovations are commonly noted in animals, but times of development of novel traits are usually unknown. We report here a novel song type arising in a bird population on an offshore island of Western Australia where the time of colonization of the island by the Western Gerygone Gerygone fusca is known. On the mainland, a single song type is widespread. On Rottnest Island, many individuals sing a different type of song and a number possess a repertoire of two song types: the standard song shared with the mainland and the novel song type not found on the neighbouring mainland. The novel song type found on Rottnest is so different in its syntactical structure that one could easily mistake it for that of a new species. The characteristic song of mainland birds is irregular in the frequencies at which the notes within a song are delivered. The novel song on Rottnest has a highly structured syntax with notes delivered at a strict and repeated sequence of frequencies resulting in a rhythmic musical sound. The species is known to have colonized Rottnest in about 1955. The new song type apparently developed rapidly by cultural evolution in the last 50 years.

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