Meeting Abstract
Low amplitude acoustic signals are often produced during social interactions at close range. In the song sparrow, ‘soft songs’ are a reliable threat signal produced during male-male aggressive interactions. A prominent explanation for low amplitude signals is the eavesdropping avoidance hypothesis (EAH), which posits that quiet signals reduce the costs associated with attracting eavesdroppers such as competitors or predators. If true, then other acoustic traits of quiet signals besides low amplitude should be adapted to decrease transmission. We tested this prediction in a field experiment by comparing the transmission properties of song sparrow ‘broadcast’ songs (normal amplitude), low amplitude ‘crystallized’ soft songs and low amplitude ‘warbled’ soft songs. We recorded all songs played at both broadcast amplitude (85 dB SPL) and low amplitude (65 dB SPL). In general, the three songs categories did not differ in transmission properties when played at the same amplitude, with the exception that at broadcast amplitude, both types of soft song had larger tail-to-signal ratios (poorer transmission) than broadcast song. However, warbled soft songs had a significantly greater signal-to-noise ratio (better transmission) compared to crystallized soft songs or broadcast songs, especially when all songs were played at low amplitude. Also, both types of soft song had lower blur ratio (better transmission) at low amplitude. In general, we find little support for the idea that soft songs are adapted to limit transmission range, and in fact, some results suggest the opposite.
