The impact of environmental noise on song amplitude in a territorial bird

1. The impact of environmental background noise on the performance of territorial songs was examined in free-ranging nightingales (Luscinia megarhynchos Brehm). An analysis of sound pressure levels revealed that males at noisier locations sang with higher sound levels than birds in territories less affected by background sounds. 2. This is the first evidence of a noise-dependent vocal amplitude regulation in the natural environment of an animal. 3. The results yielded demonstrate that the birds tried to mitigate the impairments on their communication caused by masking noise. This behaviour may help to maintain a given transmission distance of songs, which are used in territory defence and mate attraction. At the same time, birds forced to sing with higher amplitudes have to bear the increased costs of singing. 4. This suggests that in songbirds the level of environmental noise in a territory will contribute to its quality and thus considerably affect the behavioural ecology of singing males.