A rain forest dusk chorus: cacophony or sounds of silence?
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A rain forest dusk chorus consists of a large number of individuals of acoustically communicating species signaling at the same time. How different species achieve effective intra-specific communication in this complex and noisy acoustic environment is not well understood. In this study we examined acoustic masking interference in an assemblage of rain forest crickets and katydids. We used signal structures and spacing of signalers to estimate temporal, spectral and active space overlap between species. We then examined these overlaps for evidence of strategies of masking avoidance in the assemblage: we asked whether species whose signals have high temporal or spectral overlap avoid calling together. Whereas we found evidence that species with high temporal overlap may avoid calling together, there was no relation between spectral overlap and calling activity. There was also no correlation between the spectral and temporal overlaps of the signals of different species. In addition, we found little evidence that species calling in the understorey actively use spacing to minimize acoustic overlap. Increasing call intensity and tuning receivers however emerged as powerful strategies to minimize acoustic overlap. Effective acoustic overlaps were on average close to zero for most individuals in natural, multispecies choruses, even in the absence of behavioral avoidance mechanisms such as inhibition of calling or active spacing. Thus, call temporal structure, intensity and frequency together provide sufficient parameter space for several species to call together yet communicate effectively with little interference in the apparent cacophony of a rain forest dusk chorus.
KeywordsKatydids Acoustic interference Western Ghats Acoustic communication network Paleotropical cricket assemblage
We thank the Ministry of Environment and Forests, Government of India for funding and the Karnataka State Forest Department for permits. RD is supported by CSIR, India. Many thanks to Vivek Nityananda, Natasha Mhatre and Chandra Sekhar Seelamantula for help with computer codes, Hastagiri Prakash for suggestions on the algorithm for simulation for pairwise ASO and to Sudhakar Gowda and Hanumanthan Raghuram for help with fieldwork. We thank two anonymous referees and the Associate Editor for suggestions that greatly improved the manuscript. Author contributions: MJ carried out the work on ASO, SD on ETO, JB on EAO in natural choruses, RD statistical analyses and figures, RB designed the study, RB and MJ wrote the manuscript. Data and codes are available from the authors. This article is dedicated to Otto von Helversen.
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