Acoustic ranging in Poison Frogs – Allobates femoralis uses signal cues beyond intensity to assess caller distance (#535)
Acoustic ranging – to properly asses the distance of a sound source, like a competing male – is especially important for animals that live in highly territorial systems. In this context, it is often used to maintain individual spacing in order to avoid costly physical conflicts between neighbouring individuals. At the same time accurate ranging allows territory holders to make reliable decisions when to engage other callers that might be competing for space and mates. To assess intensity independent ranging in frogs, we performed playbacks with the Neotropical poison frog Allobates femoralis. Males of this species are known for their stable, long-term territories, which they announce by prolonged advertisement calling. We simultaneously recorded advertisement calls across 0.75, 1.5, 3, 6, 12, and 24 m in Neotropical rainforest, the natural habitat of the study species, to obtain naturally degraded and reverberated signals. These signals were normalised and broadcast at equal intensity from an equal distance to territorial males. Males showed significantly differential responses to signals recorded from different distances, with close, less degraded, and less reverberated recordings eliciting much stronger responses than far ones. The threshold for aggressive phonotaxis corresponded with previously measured territory sizes in the study population. This clearly shows that also frogs can perceive and evaluate signal characteristics beyond intensity to assess the distance of a sound source and to maintain inter-individual distances.