Temporal change of the song of a local population of the Grey Warbler (Gerygone igata): has its song changed over time?

The songs of bird species can vary from place to place and such variation may reflect ecological heterogeneity within the habitat. However, there is little understanding of how this process occurs over time within the same population. Here, change in song over time in a local population of the New Zealand Grey Warbler (Gerygone igata) was investigated. Spectral and temporal aspects of the song were compared in the same population at an interval of 7 years (2002 and 2009). There was a significant shift in the song syllables to a higher frequency but no difference in the temporal structure of the song. The frequency difference in song suggests that interspecific interactions may have led to song-frequency displacement, which in turn may be caused by the reintroduction of other native species to the study area.