Acoustical interference in the advertisement calls of the midwife toads (Alytes obstetricans and Alytes cisternasii)

We address the issue of whether call alternation is a mechanism for diminishing can overlap between male midwife toads who an competing acoustically. Additionally, we study the effect of call overlap on the calling behavior of males and on female preferences. In both species, naturally interacting males emitted calls that did not overlap less than expected when males called randomly. Interactive playback calls showed that males increase their calling rate when responded to by a non-overlapping call, and that they do not increase their calling rate when responded to by calls that overlap with their own calls. In phonotaxis tests, females discriminated against duets of males that overlapped their calls. Furthermore, when calling males overlapped the males' calls, females did not discriminate between the male who was leading a calling duet and the follower. We conclude, therefore, that call overlap plays an important role in communication, since overlapping calls are less attractive to females. However, timing of male calling interactions does not diminish the overlap between calls.