A global meta-analysis reveals more variable life histories in urban birds compared to their non-urban neighbours

Abstract

AbstractCities pose a major ecological challenge for wildlife worldwide. Phenotypic variation is a pivotal metric to predict evolutionary potential in response to environmental change. Recent work suggests that urban populations might have higher levels of phenotypic variation than non-urban counterparts. This prediction, however, has never been tested across taxa nor over a broad geographical range. Here, we conduct a meta-analysis of the urban avian literature to compare urban versus non-urban means and variances for phenology and reproductive performance. First, we show that urban birds reproduce earlier and have smaller broods than non-urban ones. Second, we demonstrate that urban populations have a more variable phenology than non-urban populations. Our analyses reveal that the latter pattern arises from differences in phenological variation between individuals within breeding seasons, likely because of higher heterogeneity in the urban study areas. These findings suggest that the opportunity for selection on phenology may be stronger in urban bird populations and that the patterns of phenotypic variation in urban and non-urban avian populations may consistently differ.