Bird songs on the shelf: assessing vocal activity and output using data hidden in sound archives

Abstract

Understanding how often do animals emit communication signals is of critical importance to address a variety of research questions in behavioral ecology and sexual selection. However, information on vocal output, a central component of investment in signaling, is lacking for most species employing acoustic communication. Because this lack of information is partly due to logistical and methodological difficulties in monitoring animal signaling over time, developing new approaches to quantify vocal output is of special importance. We asked whether the number of recordings of avian vocalizations in sound archives and the times when such recordings were obtained reflect estimates of vocal output and temporal patterns of vocal activity obtained through systematic monitoring of wild bird populations in tropical forest sites. Based on a sample of 43 montane forest species, we found significant relationships between the number of recordings of species detected through continuous monitoring over several months and the number of recordings archived in sound collections, especially when accounting for the area of distribution of each species. In addition, daily activity patterns based on data collected through continuous monitoring over several days did not differ from those based on recordings archived in sound collections in 12 of 15 species of lowland forest birds. Annual patterns in vocal activity of two species estimated based on recordings in collections closely resembled previously published patterns. We conclude that recordings in sound collections contain valuable yet previously unappreciated information about the vocal output and temporal patterns in vocal activity of birds. This opens the possibility of using sound collections to assess vocal output and to consider it as a variable of interest in studies on the ecology and evolution of birds and other animals that use acoustic signals for communication. We encourage field workers to keep the ears wide open, and the recorders wide ready to record.