Foraging Ecology Differentiates Life Stages and Mercury Exposure in Common Terns (Sterna hirundo)

Annie M. Bracey, Matthew A. Etterson, Frederick C. Strand, Sumner W. Matteson, Gerald J. Niemi, Francesca J. Cuthbert, Joel C. Hoffman

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Some populations of common terns (Sterna hirundo) breeding at inland lakes in North America are declining, including the Laurentian Great Lakes. Terns nesting at inland colonies forage in freshwater during the breeding season and primarily in coastal marine environments during the nonbreeding season. As piscivores, they are susceptible to dietary Hg exposure. To characterize patterns of Hg exposure in this population, we 1) quantified within and among season differences in total mercury (THg) concentrations (μg/g) in blood and feathers at 2 Lake Superior breeding colonies, and 2) documented spatial and temporal variation in exposure by studying adult foraging ecology using geospatial tracking devices and stable isotopes. We used general linear models to assess the relationship between isotopic composition and THg concentrations in bird tissues relative to sex, age, colony location, and season. The THg concentrations were lowest in winter-grown feathers (geometric mean [95% confidence limits]): 1.32 (1.09–1.59) μg/g dw (n = 60), higher at the more industrially influenced colony (chick feathers: 4.95 [4.62–5.37] μg/g dw [n = 20]), and increased with a riverine-based diet. During the breeding season, Hg exposure varied along a gradient from lake to river, with adult females having lower blood THg concentrations than males (females: 0.83 [0.67–1.03]) μg/g ww (n = 7); males: 1.15 (0.92–1.45) μg/g ww (n = 5). Stable isotope values suggested adults obtained 42 ± 12% (n = 12) of their diet from the river during incubation, which was validated with tracking data. During chick-rearing, chicks obtained 68 ± 19% (n = 44) of their diet from the river. Our results indicate colony location, foraging behavior, and season influenced Hg exposure for these Lake Superior colonies and underscores the importance of local contamination with respect to exposure. Integr Environ Assess Manag 2021;17:398–410.

Original languageEnglish (US)
Pages (from-to)398-410
Number of pages13
JournalIntegrated environmental assessment and management
Issue number2
StatePublished - Mar 2021

Bibliographical note

Funding Information:
The authors thank T Will for supporting this project; D Lyon for advice on deploying tracking devices; D Evers for providing support and advice; ICT Nisbet, M Gochfeld, and J Burger for advice; K Rewinkel, A Liljenquist, B Dhuey, J ReesLohr, and T White for field assistance; and S Janssen and J Nichols for review of the manuscript and to several anonymous reviewers. AM Bracey was supported by grants from the US Fish and Wildlife Service (USFWS; agreement no. F16AC00214, F11AP00081, and F11AP00515); the USFWS Great Lakes Fish and Wildlife Restoration Act (agreement no. F16AP01000); the Coastal Zone Management Act of 1972, as amended, administered by the Office for Coastal Management, National Oceanic and Atmospheric Administration, under award no. NA16NOS4190119 provided by the Minnesota Department of Natural Resources for Minnesota's Lake Superior Coastal Program; and by various internal grants from the University of Minnesota, including the Thesis Research Travel Grant, EVCAA Research and Scholarship Grant, the Regents Scholarship Program, and the University of Minnesota Conservation Sciences graduate program travel grant. External grants from the Minnesota Ornithologists' Union and the Duluth‐Superior Area Community Foundation provided support for analytical and monitoring efforts. AM Bracey and GJ Niemi were supported by the Natural Resources Research Institute; FC Strand and SW Matteson were supported by the Minnesota and Wisconsin departments of Natural Resources and the Natural Resources Foundation of Wisconsin and the Pittman‐Robertson Federal Aid‐in‐Restoration Act; and FJ Cuthbert was supported by the USDA National Institute of Food and Agriculture, Hatch project 1007020. JC Hoffman and MA Etterson were supported by the Environmental Protection Agency Center for Computational Toxicology and Exposure, Great Lakes Toxicology and Ecology Division. AM Bracey, GJ Niemi, and FC Strand conceived the idea and supervised research. AM Bracey, FC Strand, and SW Matteson collected data. AM Bracey, JC Hoffman, and MA Etterson analyzed the data. AM Bracey wrote the manuscript with assistance from JC Hoffman and MA Etterson, with all authors contributing to revisions.

Publisher Copyright:
© 2020 SETAC


  • Avian
  • Foraging ecology
  • Mercury
  • Migration
  • Stable isotopes
  • Environmental Monitoring
  • Mercury/analysis
  • Charadriiformes
  • Male
  • North America
  • Animals
  • Feathers/chemistry
  • Female

PubMed: MeSH publication types

  • Journal Article


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