The city blues of an iridescent canary: physiological, behavioral, and developmental impacts of lead (Pb) on songbirds along an urban-to-rural gradient

Urbanization is rapidly changing the environment and creating new challenges in the lives of animals across the globe. Anthropogenic contaminants found commonly in old construction materials—including heavy metals like lead— persist within the environment for prolonged periods of time and present a widespread problem for all who live near contaminated areas. Despite the phase-out of lead usage, it continues to threaten the health of all organisms but especially those from urban areas where historical lead use was more common. Currently, the sub-lethal effects of lead on wildlife are not well understood, though lead is known to affect physiology and behavior in humans. In response to higher concentrations of lead, animals may have to make trade-offs in order to survive within urbanized habitats. In this study, we used a common urban adapter, the European starling (Sturnus vulgaris), to explore how lead exposure is correlated with behavior, physiology, and feather development along a gradient of urbanization. We captured 125 free-living starlings to measure feather lead concentrations, along with aggression, corticosterone, and testosterone. We also measured soil lead concentrations across an urbanization gradient to test whether environmental availability was correlated to lead in starling feathers. Using linear mixed models, we found that urban starling nestlings had elevated feather lead concentrations compared to rural nestlings. However, we found no correlations between nestling feather Pb and endocrine, behavioral, or developmental traits. We also found no correlation between lead and urbanization in adults, as well as no significant differences in soil Pb concentrations between our study sites. Our findings suggest that nestling starlings may be a biomonitoring tool to detect lead in the local environment, and that non-invasive feather sampling is a promising tool beyond sampling soil alone. Further work needs to be conducted to understand the intricate relationship between heavy metals, behavior, morphological development, and physiology in free-living organisms