Understanding the evolutionary and ecological mechanisms that shape the spatial divergence of signals involved in reproductive isolation is a central goal in studies of speciation. For birds with innate songs, such as the suboscine passerine birds, the integration and comparison of both genetic and ecological factors in explaining song variation at the microevolutionary scale is rare. Here we evaluated the evolutionary and ecological processes underlying the variation in the songs of the Atlantic Forest endemic Drab-breasted Bamboo Tyrant (Hemitriccus diops), testing the effects of both stochastic and adaptive processes, namely the Stochastic and Adaptation Acoustic Hypotheses, respectively. We combined vocal, genetic and ecological (climate and forest cover) data across the species’ range. To this end, we analyzed 89 samples of long and short songs. We performed analyses on raw and synthetic data song variables with linear mixed models and multivariate statistics. Our results show that both song types differ in spectral features between the two extant phylogeographic lineages of this species, but such vocal divergence is weak and subtle in both song types. Overall, there is a positive relationship of acoustic distances with the amount of forest cover in long songs. Our results suggest that there is cryptic geographical variation in both song types and that this variation is associated with low levels of genetic divergence in both songs and with ecological factors in long songs.

Songs of H. diops were obtained from our field work, other researchers’ private collections and public libraries. Public online libraries from which songs were obtained included Xenocanto (http://www.xeno-canto.org), Wikiaves (http://www.wikiaves.com/), Macaulay Library (https://www.macaulaylibrary.org/) and the Jacques Vielliard Neotropical Music Library of the State University of Campinas (FNJV). The vocal sampling corresponds to most of the species range in the Brazilian Atlantic Forest. 

First, we evaluated the vocal repertoire of H. diops with sonograms generated in Raven Pro 1.4 (www.birds.cornell.edu/raven, Charif et al. 2010). After inspecting all available recordings and based on our field experience, a long and a short song were identified based on their acoustic structure. The long song of H. diops is a harmonic trill with a duration of ca. 1 second and with a high number of fast delivered notes . The short song is a harmonic trill with a duration of ca. 0.2 seconds and with a small number of fast delivered notes. 

This data set contains 19 acoustic variables and 8 ecological variables. Also, we included the genetic distances between populations.

For more details view: Ecological and evolutionary drivers of geographic variation in songs of a Neotropical suboscine bird: The Drab-breasted Bamboo Tyrant (Hemitriccus diops, Rhynchocyclidae). The Auk: Ornithological Advances.