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 diminis hing can overlap between male midwife toads who an competing acoustically. Additionally, we study the effect of call overlap on the calling behavior o f males and on female preferences. In both species, naturally interacting m ales emitted calls that did not overlap less than expected when males calle d randomly. Interactive playback calls showed that males increase their cal ling 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 t heir own calls. In phonotaxis tests, females discriminated against duets of males that overlapped their calls. Furthermore, when calling males overlap ped 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 interaction s does not diminish the overlap between calls.