Song variation and habitat structure in the Golden Bowerbird

Abstract

Variation is a commonly reported feature of the signals of many animal species. One hypothesis that seeks to explain this variation, the Acoustic Adaptation Hypothesis, suggests that selection should shape the structure of long-distance signals to maximise their transmission through different habitats. One prediction of this hypothesis is that signals will be designed such that within local habitats, local dialects will experience less degradation during transmission than will foreign dialects. We tested this prediction as part of a study of geographical variation in the song of the Golden Bowerbird (Prionodura newtoniana). Our aim was to evaluate the significance of local habitat structure in selection for divergent song in this species. We played both local and foreign dialects at four locations and re-recorded the song at 2 m and 50 m distance from the speaker. Song degraded differentially at the four locations, indicating the existence of different acoustic environments. However, songs that exhibited the least degradation did not originate from the locations that induced the greatest degradation. Most significantly, in local habitats, local dialects suffered similar levels of degradation to foreign dialects. These results suggest that local habitat structure has relatively little effect on the design of acoustic signal in the Golden Bowerbird at the individual level. While efficiency of transmission may influence signal design on evolutionary time-frames, conflicting social and ecological pressures probably act to reduce its importance in ecological time-frames.