Variation in syllable structure and singing behavior in a population of dusky flycatchers (empidonax oberholseri)

Abstract

Perching birds (Passeriformes) are divided into two sub-orders, the oscines and the suboscines. The suboscines make up 20% of living passerines, but relatively few studies address song function in this group. I document patterns of intra- and interindividual song variation within a population of Dusky Flycatchers (Empidonax oberholseri), a suboscine, as a first step in investigating song function. I provide evidence to support the hypothesis that song syllables are more variable in structure among than within individual males for data from both single recordings and multiple recordings made over a breeding season. This variation would allow individual recognition to occur using songs. To further examine song function, I document diurnal and seasonal patterns of singing behavior in individuals. I provide evidence to support my second hypothesis, that dawn and daytime singing have functions that are at least partially non-overlapping. Singing behaviors were qualitatively and quantitatively different between dawn and daytime singing in both 2001 and 2002. Dawn and daytime singing were influenced differently by weather, population density, and breeding stage. These results provide clues into function and evolution of song in this group, as suboscines songs probably develop innately, whereas oscine songs are at least partially learned.