Foster's Tern (Sterna forsteri) While Hunting in Flight

Photo of Foster's Tern (Sterna forsteri) while hunting. Forster’s terns are among the most at-risk wildlife species to mercury toxicity in western North America. USGS scientists have have found that body symmetry of Forster's terns (Sterna forsteri) in the San Francisco Bay are is related to blood and feather mercury concentrations. Body asymmetry can affect a bird's fitness by reducing flight efficiency, thus increasing energetic costs (especially during migration) and interrupting normal feeding and breeding behaviors.