Timing Is Everything: Acoustic Niche Partitioning in Two Tropical Wet Forest Bird Communities

Abstract

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.

When birds sing at the same pitch, they avoid singing at the same time

“…For instance, in one tropical community, birds which sang in the same frequency band as cicadas were shown to sing less often during cicada choruses (Hart et al 2015), and in another tropical community, birds which sang in crowded frequency bands avoided temporal overlap with other birds within their own frequency band (Planqu e & Slabbekoorn 2008). Other studies have found similar evidence that supports the idea that temporal avoidance tends to be stronger with greater frequency overlap (Malavasi & Farina 2013, Hart et al 2021.…”

The circadian calling activity of a lebinthine cricket with high-frequency calls is unaffected by cicada choruses in the day

“…This result validates the idea that recording eneopterine crickets in isolation under artificial laboratory conditions can still offer meaningful information about their natural circadian rhythms. This also suggests that the observed pattern is predominantly influenced by the individual’s intrinsic biological clock ( Fergus & Shaw, 2013 ) and abiotic environmental cues such as light ( Clink et al, 2021 ; Feng & Bass, 2016 ), rather than social cues from conspecifics ( Favreau et al, 2009 ; Fuchikawa et al, 2016 ) or the presence of other acoustically signalling species ( Hart et al, 2021 ).…”

“…Acoustic signalling for mate attraction and territory defence is common across animals, and signals often follow predictable circadian rhythms that reflect the ecology of each species ( Schmidt & Balakrishnan, 2015 ; Rivas, da Bauzer & Meireles-Filho, 2016 ). Many factors can influence the circadian rhythm of acoustic signalling, such as changes in light and temperature ( Clink et al, 2021 ; Feng & Bass, 2016 ), endogenous time-keeping mechanisms ( Fergus & Shaw, 2013 ), social cues from conspecifics ( Favreau et al, 2009 ; Fuchikawa et al, 2016 ), the presence of other acoustically signalling species ( Hart et al, 2021 ), or a combination of these factors. When co-occurring species have similar circadian rhythms, the Acoustic Niche Hypothesis (ANH) predicts that selection will favour differences in signalling behaviour to help reduce errors in recognition and avoid acoustic interference ( Krause, 1993 ; Farina, 2014 ).…”

“…When co-occurring species have similar circadian rhythms, the Acoustic Niche Hypothesis (ANH) predicts that selection will favour differences in signalling behaviour to help reduce errors in recognition and avoid acoustic interference ( Krause, 1993 ; Farina, 2014 ). These differences may include producing sounds at different frequencies ( Krishnan, 2019 ; Allen-Ankins & Schwarzkopf, 2022 ) or avoiding temporal overlap on short time scales ( Hart et al, 2021 ). Community-wide partitioning of acoustic space in time and frequency suggests long-term adaptation to local acoustic environment ( Farina, 2014 ).…”

“…Tropical forests, due to their high biodiversity, tend to have more severe competition for acoustic niche-space than temperate habitats ( Hart et al, 2021 ). In many Southeast Asian forests, the choruses of crickets and cicadas are among the most ubiquitous and conspicuous sounds.…”