Timing is everything: 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 partition
acoustic space and minimize overlap with other calling individuals through
selection on signal structure and/or the sender’s ability to adjust the
timing of signals. Alternately, under the acoustic clustering hypothesis,
there is potential benefit to convergence and synchronization of the
structural or temporal characteristics of signals in the avian community,
and organisms produce signals that overlap more than would be expected by
chance. Interactive communication networks may also occur, where species
living together are more likely to have songs with convergent spectral and
or temporal characteristics. In this study, we examine the fine-scale use
of acoustic space in montane tropical wet forest bird communities in Costa
Rica and Hawai‘i. At multiple recording stations in each community, we
identified the species associated with each recorded signal, measured
observed signal overlap, and used null models to generate random
distributions of expected signal overlap. We then
compared observed vs. expected signal overlap to test predictions
of the acoustic niche and acoustic clustering
hypotheses. We found a high degree of overlap in the signal
characteristics (frequency range) of species in both Costa Rica and
Hawai‘i, however, as predicted under ANH, species significantly reduced
observed overlap relative to the random distribution through temporal
partitioning. There was little support for acoustic clustering or
the prediction of the network hypothesis that species segregate across the
landscape based on the frequency range of their
vocalizations. These findings constitute strong support that
there is competition for acoustic space in these signaling communities,
and this has resulted primarily in temporal partitioning of the
soundscape.