Signal information of bird song changes in human-dominated landscapes

Communication systems rely upon specific social contexts and environments that permit effective transmission, and thus, are particularly vulnerable to disruption by anthropogenic disturbance. The acoustic environments of cities may affect conspecific interactions by altering the transmission or reception of song in ways that might ultimately influence fitness, however, the evolutionary and ecological consequences of altered songs remain poorly understood. We hypothesized that the relationship between bird song attributes and fitness metrics would be landscape-dependent, differing between urban and rural habitats. We investigated this hypothesis by measuring vocal and breeding behavior of 54 male Northern Cardinals (Cardinalis cardinalis) at nine sites distributed across a rural to urban landscape gradient in Columbus, Ohio in 2011. Interestingly, we found evidence that relationships between song attributes and male quality differed among landscapes. Shorter and slower songs were associated with larger males in more preferred territories (i.e. with denser vegetation), but only in rural landscapes. Across all landscapes, males that sang at high frequencies had nestlings in poorer condition, but otherwise song attributes were not associated with reproductive output or male provisioning ability. Our results suggest that urban landscapes change the function of song as a signal of quality and could reduce the usefulness of song as a predictor of reproductive performance. This is one of few studies to investigate signal relationships and potential fitness consequences of song variation in natural urban systems, thereby providing insight into micro-evolutionary processes operating within novel environments.