Calling tactics in Crinia georgiana (Anura: Myobatrachidae): alternation and variation in call duration

Male Crinia georgiana actively alternate with artificial stimulus pulses at rates of stimulation encountered in natural choruses. Males also increase the duration of their calls by adding notes in response to increased frequency of acoustic stimulation. We interpret this result to be an adaptation that allows males to maintain broadcasting periods (interference free) at least as long as those ofcompetitors. Alternation is facilitated by a 0.4-s post-stimulus lag period. Evoked calls are not initiated during the lag period which, together with the 0.3-s stimulus pulse, approximates the duration of a three-note call; such calls predominate in natural choruses. Evoked calls that were likely to overlap a following stimulus pulse were terminated, minimizing interference and demonstrating the importance of effective signal transmission.