Acoustic signals play fundamental roles in anuran communication by facilitating social interactions, and for many species, successful reproduction depends on long-range propagation and perception of advertisement calls. Several anurans have been shown to exploit habitat features, such as tree holes for their resonance effects, to improve mating call transmission. In an urban environment, such habitat features might also include man-made structures that animals learn to use for acoustic communication. In Taiwan, male Mientien tree frogs Kurixalus idiootocus frequently perch and call in roadside concrete drainages, suggesting that they are using these anthropogenic structures to assist call transmission. The authors of a paper recently published in Journal of Zoology tested this assumption by a combination of field and indoor experiments. Wen-Hao Tan et al. conducted a field survey of whether male Mientien frogs preferred calling inside the storm drains than outside them, and a playback experiment in the field to verify whether the propagation of calls emitted inside drains is enhanced. They also constructed a replica of a concrete drain in the lab to study whether male frogs selected perches inside the drains that facilitated better call transmission.
The field survey indicated that male Mientien tree frogs preferred calling inside rather than outside drains, and the playback experiment showed that calls emitted from inside drains were enhanced in both amplitude and note duration. The lab experiment showed that males preferred a particular type of call perch, although there was no difference in sound properties between random locations inside the drain model and the preferred perch location. Although it still needs to be verified whether the enhanced call transmission of male Mientien frogs calling inside the storm drains also means that they have better mating success, with these ‘urban canyons’, this study shows a novel effect of anthropogenic structures on bioacoustics.