Tropical wrens rely more on acoustic signals than visual signals for inter- and intraspecific discrimination

Animals may use multiple signalling modalities to discriminate between conspecific versus heterospecific animals, or between individuals that represent a threat versus a mating opportunity. Multimodal signals used in intra- and interspecific discrimination can serve as redundant signals, or each modality may convey unique information. Furthermore, signals in different modalities may show different transmission properties through different habitats. In this study we investigated how two congeneric wrens, rufous-and-white wrens, Thryophilus rufalbus, and banded wrens, Thryophilus pleurostictus, use acoustic and visual signals for species discrimination in tropical forest habitats. We coupled song playback experiments with visual models to assess the importance of these signals, both in combination and in isolation. We assessed vegetation density in the territories of both species to assess whether more densely vegetated territories influence the use of visual signals. We presented both rufous-and-white wrens and banded wrens with conspecific and congeneric song treatments, model treatments and song-accompanied-by-model treatments. We found that both species responded strongly to song and song-accompanied-by-model treatments, but showed little or no response when the model was presented alone. These results suggest that wrens rely heavily on acoustic signals and very little on visual signals for discrimination. The species differed in their response to conspecific and congeneric trials, with rufous-and-white wrens showing little response to the congeneric trials but banded wrens responding strongly to both conspecific and congeneric trials. The asymmetrical response to the playback trials suggests that there may be a social dominance relationship between these two species, with rufous-and-white wrens being dominant over banded wrens. No previous studies have investigated the relative importance of acoustic and visual signals in males and females for species discrimination. Our results suggest that acoustic signals are more important than visual signals for inconspicuous animals living in dense environments. © 2016 The Association for the Study of Animal Behaviou