Female bird song rates do not covary with population density in a North American species

Abstract

AbstractBird song can vary across space and time or within different social environments. These variations in bird song have historically been considered from the perspective of males, particularly in North American temperate regions. In this study, we explored possible changes in singing behavior by females of a North American species, the canyon wren (Catherpes mexicanus). Male and female canyon wrens sing sex‐specific songs to defend resources. Females rarely sing spontaneously but sing readily when challenged with playback. We sought to determine whether the rarity of spontaneous female song seen in previous studies stems from low population density. In areas with higher population density, female canyon wrens should encounter neighbors and competitors for resources more often, potentially driving up song rates. We examined female song rates both within a single population and compared between two populations, hypothesizing that females with closer neighbors would (1) sing more often without playback and (2) sing with more aggressive features in their songs and behave more aggressively in response to playback. We estimated population density on the ground using nearest‐neighbor distances and verified these with eBird abundance models. We did not find that population density predicted rates of spontaneous song. Most song characters and playback response behaviors also did not vary with local canyon wren abundance. Females from our denser population sang with significantly lower pitch, but we attribute these differences mostly to geographic variation. Although population density is known to drive patterns and rates of male song behavior, it may be less important in determining female song behavior.