Urban Dependent Selection on Bird Song

Recording white-crowned sparrows holding territories in the Battery West section of the Presidio in San Francisco, CA.

Human activity has modified habitats and altered ecological and evolutionary processes around the world. Urban environments are some of the most highly modified habitats on the planet, as human density continues to increase in cities. Despite this, many species persist in urban settings. Most research has focused on the effects of urbanization on species diversity and conservation. Surprisingly, there has been comparatively little investigation into adaptations of species that remain in urban environments.

We are investigating the factors that influence the evolution of bird song in the urban environment. We have a unique opportunity to compare current and historical songs from urban and rural habitats for a subspecies of white-crowned sparrows (WCS, Zonotrichia leucophrys nuttalli) and will use this system to compare evolutionary trajectories of each location. Our previous research found an increase in low frequency urban noise in San Francisco, CA over a 30-year period. As predicted by signal detection theory, we found a concomitant increase in minimum frequency of WCS songs (Fig 1).

Building on these findings, our study will address three fundamental questions: (1) how are birds adjusting their song to the urban environment?; (2) how has song urbanization affected signal salience?; and (3) are urban songs adaptive? To address these questions, this study is using hand-rearing experiments, female choice tests, collection of behavioral and ecological data in the field, and development of the first mechanistic, individual-based model of quantitative song evolution, to investigate the mechanisms and consequences of song evolution in an urban environment. This work will transform our state of understanding of urban-dependent selection on mating behaviors and, more broadly, the adaptations of species that persist in urban environments. Results will inform both our understanding of how acoustic communication systems evolve as well as urban conservation efforts.