Vocal behavior and microgeographic variation in song types in a Neotropical songbird

Characterizing the vocal repertoires of bird species is a first step to understanding the diversity of their vocalizations and their use in social and sexual contexts, as well as to uncover temporal and geographical patterns in vocal variation. Despite the high species richness of the Neotropical avifauna, vocal repertoire sizes and the function of vocalizations of species remain poorly documented compared to species from the North-temperate zone. We present the first qualitative and quantitative description of the vocal repertoire, diel variation in vocal activity and song-type sharing of the Gray-browed Brushfinch (Arremon assimilis), an Andean understory songbird, based on recordings of vocalizations obtained for 33 territorial pairs from the Colombian Andes. We found that A. assimilis produces four types of calls, solo songs emitted separately by individuals of each sex, and duets. By classifiying 7830 songs, we estimated that males have on average 9.6 ± 1.9 song types involving high-pitched, modulated elements combined in various ways. Similarity in repertoire-use declined with distance between neighbors to the point that no song types were shared among individuals located in sectors separated by only 2 km. Vocal activity peaked in the early morning for calls and male songs, whereas calls showed an additional peak near dusk. Our results provide the first evidence of female solo song and duets in A. assimilis, which are seemingly rare behaviors among Neotropical sparrows. The pattern of microgeographical variation in song-type sharing we observed has not been documented in similar studies of other tropical avian species.