Loss of Function in Territorial Song: Comparison of Island and Mainland Populations of the Singing Honeyeater (Meliphaga virescens)

Abstract

I studied vocal recognition in populations of Singing Honeyeaters (Meliphaga virescens) on Rottnest Island and the adjacent mainland of Western Australia through song-playback experiments. Morphological evidence suggested the island population had differentiated. I addressed the question of whether there was divergence in the vocal signaling system, I found significant loss of function of the territorial advertising song by comparing responses of the Rottnest subjects and those of subjects from the mainland Nedlands population. The low level of response by Rottnest birds to songs from the mainland was similar to the response by Rottnest birds to songs of the co-occurring Golden Whistler (Pachycephala pectoralis). On the mainland, Nedlands birds responded to the songs of another mainland population, located the same distance away as Rottnest Island, at an elevated level similar to their response to songs of their own Nedlands population. I conclude that there are population-specific vocal features in the songs of Rottnest Singing Honeyeaters that result from isolation. The isolation caused by the water barrier between Rottnest Island and the mainland is greater than isolation by distance through continuous populations on the mainland. I speculate that vocal recognition was probably lost as a result of an early colonization of Rottnest and the subsequent establishment of a new vocal tradition in the island birds.