Exposure to Heavy Metals in American Robins: Impacts and Implications

Abstract

American robins are a common bird in a variety of habitat types across North America, such that they have the potential to serve as excellent bioindicators of environmental contamination in a variety of settings. We build on previous work to develop analytical techniques such as ICP-MS and XRF for use in wildlife studies, leveraging the availability of data on robins across regions. Bone and blood samples from robins were analyzed for copper (Cu), zinc (Zn), arsenic (As), mercury (Hg), and lead (Pb) and evaluated for changes in concentration across robins of different sexes, ages, and locations, as well as inter-elemental relationships. No significant changes in bone lead levels were detected. Seasonal variations in blood Pb, Hg, and As are most likely linked to seasonal changes in diet. There are also locational differences in Pb related to the level of urbanization based on average human population size, with significantly higher blood lead levels in robins in Indiana versus those in Alaska. Evidence for translocation of Pb from blood to medullary bone in females during breeding season suggests that Pb can act as an endocrine disruptor in female robins. A significant correlation between estradiol and blood Pb as well as a slightly significant difference in blood Pb in breeding versus non-breeding females support this hypothesis. For the entire sampling pool, mercury has a significant negative correlation with estradiol, but this disappears when filtered by state. We also found that females have lower Hg levels than males likely due to egg depuration, and younger birds have lower Hg levels. Inter-elemental relationships appear to reflect sources of environmental contamination such as automobiles and lead-based products. Overall, these findings suggest that exposure to heavy metals in robins is dependent on individual-level physiology and behavior.