Acoustic and temporal birdsong measurements

In tropical birds, survival is dependent on the ability to effectively
communicate with others against a background of high ambient noise. The
Acoustic Niche Hypothesis proposes that the deterrent selective force of
signal masking has caused animals sharing a habitat to partition their
calling behaviour amongst the acoustic bandwidths available, so as to
minimise interference between one another. Whether and why species share
the so-called ‘acoustic space’ remains a gap in our understanding of
animal ecosystems. The aim of this study was to investigate differences
between the acoustic structure of avian communities in two spatially
distinct habitats in the montane tropical forests of the Caparaó National
Park in south-eastern Brazil, and to test whether the distribution of
birdsong at each conformed to the ANH. Birdsong from nine hours of passive
acoustic recordings at each study site were analysed using principal
component analyses. The results contradicted the ANH, revealing strikingly
similar patterns of synchronised vocal behaviour. No correlation was
evident between the acoustic and temporal partitioning behaviour of
songbirds. This study provides a novel comparative analysis of the
acoustic dynamics in two separate and diverse avian communities and
support for theories of synchronized vocal behaviour in such groups.