Mimus polyglottos (Northern Mockingbird) vocal mimicry reflects variation in species richness and composition along an urbanization gradient

Abstract

Urbanization consistently alters avian species richness and community composition, yet how these changes influence avian vocal mimicry remains poorly understood. Vocal mimicry is an acoustic trait found in ∼15% of the world's bird species and plays a key role in male mate attraction and quality assessment in many of these species. Declines in species richness and shifts in community composition resulting from urbanization may therefore alter mimicry behavior in ways that affect male acoustic quality and reproductive success. Here we tested the relationship between urbanization, avian community structure, and vocal mimicry behavior in Mimus polyglottos (Northern Mockingbird) across an urbanization gradient in north Florida, USA. We hypothesized that (1) overall avian richness would decline with increasing urbanization; (2) sites with similar community compositions would also support mockingbirds with similar mimicry repertoire compositions; and (3) declines in species richness would be associated with decreases in 4 acoustic variables: the number of species mimicked (mimicry richness), the number of unique mimetic syllable types produced (mimicry complexity), the proportion of song composed of mimetic elements (mimicry usage), and the total number of unique syllable types (song complexity). As hypothesized, species richness declined significantly across the gradient, and M. polyglottos mimicry repertoire composition significantly reflected local avian community composition. Site-level avian richness was significantly positively associated with M. polyglottos mimicry richness, mimicry complexity, and mimicry usage, whereas song complexity showed no relationship with richness and hence also urbanization. Together these results demonstrate that M. polyglottos vocal mimicry behavior tracks local avian community richness and composition across an urban gradient, highlighting vocal mimicry as a potential indicator of ecological change.