High prevalence but low concentrations of blood lead (Pb) levels among trumpeter swans in central North America

Lead (Pb) is a toxic heavy metal that has detrimental effects on wildlife. The toxicant is particularly relevant for species that use a muscular gizzard to digest food and that forage in areas with accumulated sediment at the bottom of lakes and streams. Poisoning from ingested spent lead ammunition or fishing tackle has been a major source of mortality of Trumpeter Swans (Cygnus buccinator) across North America. However, virtually all lead testing has been conducted on carcasses or swans brought to wildlife rehabilitation centers, and there are no baseline data from free-ranging swans. We estimated blood lead concentrations for 115 free-flying Trumpeter Swans throughout the breeding range of the Interior Population that inhabits central North America. We detected lead in all samples, but 90% of swans had blood lead levels in the ‘background’ range (< 200 ppb), 8% of swans had blood lead levels in the ‘sub-clinical’ range (200–500 ppb), and 2% of swans had blood lead levels in the ‘clinical’ (500–1,000 ppb) or ‘severe’ (> 1,000 ppb) range of lead toxicity. The swan with the highest blood lead level (1,076 ppb) was captured 3 km from a major coal power plant, although we were unable to definitively trace the source of lead (e.g., to coal ash or fishing tackle) in that individual. Our study provides useful baseline information on the prevalence and magnitude of blood lead levels among Interior Population trumpeter swans and demonstrates the apparent continued wide-scale exposure of wetland-feeding waterfowl to lead.