Acoustic niche partitioning in two tropical wet forest bird communities

When acoustic signals sent from individuals overlap in frequency and time, acoustic interference and signal masking may occur. Under the acoustic niche hypothesis (ANH), signaling behavior has evolved to minimize overlap with other calling individuals through selection on signal structure and the senders ability to adjust the timing of signals. In this study, we examine the fine-scale use of acoustic space and the relevance of the acoustic niche hypothesis in two montane tropical wet forest bird communities (Costa Rica and Hawaii) that vary in bird species richness. We used a null model approach to test the prediction that there are differences between observed and expected signal overlap in both communities. As predicted under ANH, we found much lower overlap of acoustic signals than expected by chance. In addition, spectral and temporal overlap between different signals was far more common in Hawaii than Costa Rica. These findings constitute strong support that there is competition for acoustic space in signaling communities, and this has resulted in temporal and spectral partitioning of the soundscape.