Plumage color and reproductive output of eastern bluebirds (Sialia sialis) nesting near a mercury-contaminated river

Abstract

Despite the growing evidence of mercury's impact on ecosystems, few studies have looked at the environmental impact of mercury pollution on terrestrial songbirds and the complex ways through which mercury might influence their fitness. In 2007–2008 eastern bluebirds (Sialia sialis) were monitored on mercury contaminated and reference sites for blood and feather mercury, reproductive success and plumage coloration. Higher tissue mercury accumulation was associated with plumage that was overall brighter and shifted towards the UV portion of the spectrum. In females, long-term mercury exposure, as indicated by feather mercury, was associated with smaller clutches of eggs. In males, recent mercury exposure, as indicated by blood mercury, was associated with a reduction in the proportion of hatchlings that fledged, potentially through reduced male provisioning of offspring. Reproductive success and plumage color are closely linked in bluebirds through mate choice, and our findings indicate that mercury contamination is associated with reproductive success directly and possibly indirectly, through coloration of bluebirds.

Keywords:

• Color
• eastern bluebird
• mercury
• plumage
• Sialia sialis

Acknowledgments

Research was completed with oversight from the South River Science Team, which is a collaboration of state and federal agencies, academic institutions, and environmental interests. We thank the members of the Cristol Lab at the College of William and Mary for sharing their field site and especially those who helped collect these bluebird data: Anne Condon, Rebecka Brasso, and Kelly Hallinger.