Interspecific vocal discrimination in Neotropical wrens: responses to congeneric signals in sympatry and allopatry

When animals defend resources using territorial signals, they must distinguish between competitors and noncompetitors. Conspecific animals routinely compete for resources and regularly engage in aggressive signalling exchanges. Heterospecific animals may also compete for resources, and therefore animals may direct their aggression towards heterospecific as well as conspecific rivals. In both cases, animals should benefit by discriminatingbetween nonthreatening individuals versus threatening conspecific and heterospecific competitors. Experience may play an important role in competitor discrimination; animals living in sympatrywith heterospecific competitors may gain experience with heterospecific rivals, but animals living in allopatry will not. We investigated whether experience influences species discriminationbetween two congeneric Neotropical wrens (rufous-and-white wrens, Thryophilus rufalbus, and banded wrens, Thryophiluspleurostictus) that live in sympatryin some parts of their range and in allopatry in other parts of their range. We simulated the presence of male conspecific, congeneric and control intruders in the territories of rufous-and-white wrens at sites where they are sympatric or allopatric with banded wrens. If species discriminationis influenced by experience, we predicted that wrens would always respond strongly to conspecific songs, but that in sympatry, they would respond more strongly to the congeneric competitor than to the control songs. Conversely, we predicted that, in allopatry, wrens would show similarly low responses to congener and control songs. In contrast to our predictions, we found that rufous-and-white wrens discriminatedbetween conspecific and heterospecific animals, but that this response did not differ in sympatryor allopatry, suggesting that experience with heterospecific competitors does not influence interspecific discriminationin this species. By contrasting the responses of sympatric and allopatric populations, we can better understand the effect of experience on interspecific discriminationand gain insight into the evolution of species discriminationsignals.