The acoustic adaptation hypothesis (AAH) proposes that habitat characteristics affect the evolution of birds’ long-distance vocalizations. Although many studies have confirmed the AAH, some have reported contradictory results. Thus, the role of ecological factors in bird song evolution remains unclear. Few studies have examined the role of habitat on the structure of long-distance calls of birds in the forests of Southeast Asia. I investigated the AAH for the avian community of a lowland tropical forest in southern Vietnam. In 34 passerine species, I analysed the correlations between 9 frequency, power and temporal parameters of long-distance vocalizations (generally songs) and the following factors: body mass, biotope and stratum. The results confirm the AAH predictions; in spite of significant effect of body mass on acoustic parameters, ecological factors also affected some acoustic parameters. In addition, ecological factors demonstrated the strongest correlation with power parameters, whereas body mass showed the strongest correlation with frequency and temporal parameters.
AAH, sound propagation, long-distance signal, biotope, stratum, body mass