You are here:
Foraging ecology differentiates life stages and mercury exposure in common terns (Sterna hirundo)
Citation:
Bracey, A., M. Etterson, F. Strand, S. Matteson, G. Niemi, F. Cuthbert, AND J. Hoffman. Foraging ecology differentiates life stages and mercury exposure in common terns (Sterna hirundo). Integrated Environmental Assessment and Management. Allen Press, Inc., Lawrence, KS, 17(2):398-410, (2021). https://doi.org/10.1002/ieam.4341
Impact/Purpose:
At Great Lakes Areas of Concern, a common beneficial use impairment (BUI) is degraded fish and wildlife populations, often perceived to be the effect of exposure to contaminated sediments. In the St. Louis River Area of Concern (AOC), restoring and conserving the Interstate Island common tern population is a management target under this BUI. This paper reports a study of how potential risk of exposure to mercury to both adults and chicks from the Interstate Island colony is influenced by their foraging behavior, and contrasts their risk to a colony (Ashland Island) that nests in an area where sediment contamination is relatively low.
Description:
The population of Common Terns (Sterna hirundo) breeding in interior lakes of North America is declining. As piscivores, they are particularly susceptible to methylmercury (MeHg) exposure. To determine if MeHg exposure is a potential threat to this population, we (1) quantified within and among season differences in total mercury (THg) concentrations in blood and feather tissues at two Lake Superior breeding colonies, and (2) documented spatial and temporal variation in exposure risk by studying the foraging ecology of adults using geospatial tracking devices and stable isotopes. Colony location and differences in foraging strategies influenced exposure risk. Concentrations were lowest in winter-grown feathers, highest in chick feathers, and increased with an estuarine-based diet. During incubation, adults obtained more of their diet from Lake Superior (relative to the estuary), whereas, during chick-rearing they foraged more extensively in the estuary. Our results suggest that adult Common Terns can effectively eliminate mercury during annual molts and that foraging behavior may mitigate adult exposure. However, chick feather concentrations often exceeded 5ìg/g, a threshold associated with toxicological risk, suggesting mercury 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.
URLs/Downloads:
DOI: Foraging ecology differentiates life stages and mercury exposure in common terns (Sterna hirundo)