Dynamical interactions in a green treefrog chorus.

Abstract

In southeast Texas male green treefrogs (Hyla cinerea) assemble in dense choruses and call for several hours every night to attract females. The call is a short “quank” lasting about a 100 ms, with a variable call interval of about 400 ms. Individuals call from dense vegetation surrounding the breeding area, occupying positions that range in elevation from water level to several meters above the ground. The high call-rate and duty cycle combined with their three-dimensional spatial distribution present challenging problems for signalers and receivers and for human observers. It is qualitatively apparent that within a large natural chorus, individuals dynamically adjust their calling to avoid overlap with other callers. However, the dynamical interactions and calling strategies have not been quantified. Here, a 15-microphone array was deployed within the breeding site in the vicinity of one group of callers, and the locations and call patterns of individuals were extracted by acoustic beamforming. The results show that an individual pays attention to only a few of the neighboring males and times his calls to avoid call collision. When a collision occurs one of the individuals will delay the subsequent call by approximately half a call interval to avoid further collision.