WHY STOP CALLING - A STUDY OF UNISON BOUT SINGING IN A NEOTROPICAL TREEFROG

Chorusing males of the Neotropical treefrog, Hyla microcephala, call in distinct bouts punctuated by periods of silence, known as unison bout singing. Previous studies of the calling energetics of frogs do not support the idea that males periodically stop calling because of high muscle lactate levels. Three additional hypotheses of why calling periodically ceases were tested. A two-stimulus female choice experiment failed to support the hypothesis that females prefer males that call cyclically. Playback experiments with males in the field rejected the hypothesis that males stop calling because of high ambient noise. Rather, data indirectly supported the hypothesis that males cease calling to save energy. Male H. microcephala adjust the timing of notes in their multi-note calls when interrupted by notes of other males. The flexibility of note timing was tested by interrupting males with call-triggered computer-generated advertisement calls of 20-1000 ms. The vocal behaviour of the frogs reduced acoustic interference significantly for most stimulus durations and probably allows males to minimize note overlap with their closest neighbours in the chorus while continuing to call when chorus noise levels are high. © 1991 The Association for the Study of Animal Behaviour.