The spatio-temporal analysis of male-male vocal interactions in chorusing frogs

Abstract

In some chorusing frog species, such as the green treefrog (Hyla cinerea), males can rapidly adjust call-timing with reference to neighbors and avoid acoustic interference while maintaining call-rate. The rules underlying vocal interactions are largely unknown, presumably being species-specific and governed by acoustic and physiological factors. Here, we use a microphone-array technique that can simultaneously localize callers and selectively extract the calls of each frog. This allows us to analyze vocal interactions between individual callers at high spatial and temporal resolutions. We show that green treefrogs can synchronize with one another and prefer to time their calls antiphonally that are on average exactly at one-third and two-thirds of the inter-call intervals of a focal neighbor. When antiphonal calling is not possible, call collision is tolerated even though a continuum of phase positions are available. The communication system in green treefrogs is thus “discrete” with callers capable of rapidly switching between the discrete phase-slots (0, 1/3, and 2/3) in response to changes in a neighbor’s phase. Further, call collision increases and phase-locking decreases, with increasing inter-caller spacing. We conclude that the vocal communication system in green treefrogs is capable of robust maintenance of inter-caller timing so as to maintain chorus synchrony.