Song variation among Chatham Island Warblers on two islands of the Chatham Island archipelago

Biogeography plays an important role in the evolution of song structure in passerine birds. On two islands of the Chatham Island archipelago, songs of Chatham Island Warblers (Gerygone albofrontata) differed in both form and amount of variation among individuals. On Chatham Island (899 km2) song structure varied little whereas on Mangere Island (1.13 km2) structure varied considerably, but with none of the songs being the same as the song on Chatham Island. Increased song variability on the smaller island is not attributable to reduced avian species richness as has been suggested for other species in comparable settings.