You are here:
How foraging behavior influences methylmercury exposure to common terns (Sterna hirundo) breeding in the St. Louis River Estuary
Citation:
Bracey, A., J. Hoffman, M. Etterson, F. Strand, S. Matteson, G. Niemi, AND F. Cuthbert. How foraging behavior influences methylmercury exposure to common terns (Sterna hirundo) breeding in the St. Louis River Estuary. St Louis River Summit, Dulluth, MN, March 03 - 04, 2020. https://doi.org/10.23645/epacomptox.11941875
Impact/Purpose:
The population of Common Terns (Sterna hirundo) breeding in interior lakes of North America is declining. There are currently only two longtime active nesting colonies on Lake Superior; Interstate Island in the Duluth-Superior harbor, within the St. Louis River Area of Concern (AOC), and Ashland Island in Chequamegon Bay, Ashland, WI. To determine if mercury exposure is a potential threat to these Lake Superior breeding colonies, we quantified within and among season differences in total mercury (THg) concentrations in blood and feather tissues of adults and chicks and documented spatial and temporal variation in exposure risk using geospatial tracking devices and stable isotopes. We conclude that long-term monitoring of this species in the St. Louis River AOC will be important to determine exposure risk post-restoration and AOC delisting.
Description:
The population of Common Terns (Sterna hirundo) breeding in interior lakes of North America is declining. This includes the Great Lakes region, where significant decreases in the number of nesting pairs and colony sites has occurred over the past several decades. There are currently only two longtime active nesting colonies on Lake Superior; Interstate Island in the Duluth-Superior harbor and Ashland Island in Chequamegon Bay, Ashland, WI. Common Terns often nest in highly urbanized coastal environments where ongoing habitat loss and fragmentation, increased human population density, and pollution contribute to ecosystem degradation. The Great Lakes region is widely contaminated with mercury and fish-eating birds, including Common Terns, are known to be at greatest risk of exposure to mercury which has been linked to reduced reproductive success, behavioral changes, and motor skill impairment. To determine if mercury exposure is a potential threat to these Lake Superior breeding colonies, we quantified within and among season differences in total mercury (THg) concentrations in blood and feather tissues of adults and chicks and documented spatial and temporal variation in exposure risk using geospatial tracking devices and stable isotopes. THg concentrations were lowest in winter-grown feathers, highest in chick feathers, and increased with an estuarine-based diet. Our results suggest that adults can effectively eliminate mercury during annual molts and egg production and that adult foraging behavior may mitigate adult exposure on the breeding grounds. Chick feather concentrations at Interstate Island often exceeded 5ìg/g, a threshold associated with toxicological risk, suggesting Hg exposure may be an important stressor for chicks, even if effects are sub-lethal, and underscores the importance of local contamination with respect to exposure and risk. Long-term monitoring of this species in the St. Louis River Estuary will be important to determine exposure risk post-restoration and AOC delisting.
URLs/Downloads:
DOI: How foraging behavior influences methylmercury exposure to common terns (Sterna hirundo) breeding in the St. Louis River Estuary