Vocal Phenology of Forest Tinamous Along a Latitudinal Gradient: Effects of Daylength and Precipitation

The phenology of bird vocalizations is increasingly employed to understand avian reproduction and territoriality, among other ecological aspects. Although precipitation is ostensibly the major driver of seasonality at the equator, subtle photoperiodic signals are discernible in daylength, with a typical variation of 20 to 25 min over the entire year. However, in hyper-diverse areas, such as the tropics, environmental cues for phenological patterns are relatively small compared to temperate regions, requiring long-term data to identify patterns of vocal seasonality. One such source of data comes from the increasing numbers of bird visual and aural records generated by citizen science initiatives, easily accessible through online platforms such as eBird. First, we validated the use of eBird citizen science data for vocal phenology research, demonstrating strong concordance with independent audio recordings. Then, we assessed the vocal phenology of forest tinamous using a large eBird dataset. This work tested the hypotheses that the vocal phenology of tropical forest tinamous is influenced by changes in daylength and precipitation. To test the effect of changes in daylength and precipitation, we grouped records of forest tinamous in five regions with similar precipitation regimes over four latitudinal bands. After filtering, we obtained a total of 44,071 records of 16 forest tinamou species between January 2000 and December 2022. We found that vocal phenology in tropical forest tinamous can be predicted by changes in precipitation but is primarily influenced by changes in daylength. There appears to be a clear difference in singing patterns between the broad regions defined by precipitation regimes. In wetter regions, the effect of precipitation was stronger. Forest tinamous vocalize mainly when precipitation is low, especially in humid regions with similar climatic regimes. They also tend to sing more when days become either longer or shorter, with the lowest vocal activity at 12 h of daylength. Questions such as these, concerning tropical phenology, have been elucidated through the contribution of citizen science to this burgeoning field.