The Seychelles Warbler Acrocephalus sechellensis is a resident, cooperative breeder in a saturated, island environment, whose song structure diners significantly from European marshland Acrocephalus species. The song is transmitted within a more restricted frequency range, that which propagates most effectively through tropical forest. The Seychelles Warbler has developed a relatively short, simple song, used for territorial defence throughout the year, which is readily elicited by playback. Yet it also has a complex repertoire of song types, and song activity peaks before and declines during breeding, suggesting a sexual function. The demands of tropical island life are thus reflected in both the structure and function of song in the Seychelles Warbler.