Regional- and season-specific exposure to lead in a common North American songbird

The determinants and physiological consequences of exposure to heavy metals remain poorly understood for songbirds. The American Robin ( Turdus migratorius ) is a common songbird in a variety of habitats across most of North America that could serve as an ideal sentinel of heavy metal contamination. We evaluated how robin exposure to lead varied regionally, seasonally and among demographic groups, and assessed impacts on body condition and reproductive hormone levels. We detected significantly higher blood lead levels in robins sampled in a more urban region (Indiana) compared to a rural region (Alaska), and blood lead levels were also highest in the spring and summer, when robins primarily forage on earthworms, which in turn likely accumulate lead due to their feeding activity and ambient soil lead contamination in more urban environments. We found no significant relationship between blood lead levels and body condition, but blood lead levels showed a negative relationship with testosterone in male robins and with estradiol in female robins, suggesting lead may have negative effects on reproductive function. Overall, these results suggest that robins could serve as reliable bioindicators of lead and its impacts on wildlife health across a broad range of ecosystems.