Response to heterospecific calls in non‐passerine species: can two Rallidae species recognise each other based on their vocalisations?

Communication is generally assumed to be the domain of conspecific signallers and receivers that produce reliable signals and respond adaptively. However, interactions between coexisting species can be surprisingly complex, suggesting that animals not only perceive but also selectively respond to signals produced by other species. Many species respond to the vocalisations of heterospecifics, but it is usually difficult to separate actual vocal recognition from the response resulting from misidentification. We controlled this bias in a playback experiment with two sympatric Rallidae species, the water rail ( Rallus aquaticus ) and little crake ( Zapornia parva ). Both focal species produced more calls and little crake additionally approached the speaker more often in response to calls of each other than to calls of closely related but non‐sympatric spotted crakes ( Porzana porzana ) or the sympatric but non‐competing little grebes ( Tachybaptus ruficollis ). By contrast, when responding to each other's calls water rails produced fewer loud calls than during the conspecific treatment suggesting that focal birds were merely announcing their presence, whereas little crakes produced mainly alarms suggesting that they communicated with the mated partner to warn it rather than with the heterospecific intruder. We conclude that focal Rallidae species could distinguish not only their calls from those of conspecifics, but also each other's calls from those of other sympatric and phylogenetically related species.