The Acoustic Adaptation Hypothesis does not support the occurrence of common songs in a neotropical urban bird species

The Acoustic Adaptation Hypothesis indicates that vocalisations will have acoustic characteristics that maximise their transmission within the habitat where they are produced. Therefore, vocalisations of the same species are expected to vary between habitats if the habitats vary in structure. We conducted a sound transmission experiment to analyse if the common songs of the White-eared ground sparrow, Melozone leucotis, an urban bird species, differ between populations because they are adapted to the characteristics of each habitat to maximise their transmission. The experiment was conducted in four isolated populations within the urban areas of Costa Rica with different habitats: secondary forests, coffee plantations, gardens and thickets. In each population, we reproduced the three common songs of each population, and we compared four song degradation measures (excess attenuation, blur ratio, signal-to-noise ratio, and tail-to-signal ratio). Contrary to our expectations, our results contradicted the Acoustic Adaptation Hypothesis, since the common songs of each population did not transmit better in their own habitat, but the songs are adapted to transmit better in the original habitat. We suggest that common songs of this bird may be selected and maintained in each population by female selection.