Date of Award


Publication Type

Doctoral Thesis

Degree Name



Biological Sciences

First Advisor

D. Mennill


bioacoustics, bird song, ornithology, speciation, tropical ecology




Animals communicate using multiple signaling modalities, with vocal and visual signals being the most prevalent in birds. The responses of animals to signal divergence among populations, along with the extent of divergence itself, may promote reproductive isolation and potentially speciation. Research on mating signal divergence, and experimental tests of responses to divergent signals, will expand our understanding of the mechanisms of reproductive isolation. In my dissertation, I investigated the form and function of vocal and visual signals in the Rufous-capped Warbler (Basileuterus rufifrons), a Neotropical resident songbird with complex song and bright plumage. I described male vocal behaviour in this species, and experimentally tested whether males and females showed seasonal variation in vocal behaviour during conspecific territorial interactions. I quantified range-wide variation in plumage, song, and morphology, and I experimentally tested whether two sympatric subspecies responded differently to each other’s songs. I found that male Rufous-capped Warblers have large, complex repertoires, and vary their singing behaviour depending on the season, time of day, and presence of conspecifics. I found that female Rufous-capped Warblers sing, which is the first report of female song in this species. Females used both songs and calls to contribute to joint territory defence, but they approached playback and sang most often in the non-breeding season. My results suggest that Rufous-capped Warblers comprise two distinct species, the northern, white-bellied B. rufifrons and southern, yellow-bellied B. delattrii, based on phenotypic differences between them and low responses to heterotypic signals by two divergent subspecies living in sympatry. My research provides insight into the vocal behaviour of tropical resident wood-warbler species, and adds to the growing number of studies showing that female signals function in territory defence in tropical songbirds. My findings also support a revision of the Rufous-capped Warbler’s taxonomic status, thus refining our understanding of biodiversity in wood-warblers and Neotropical animals.