Mercury in wing and tail feathers of hatch-year and adult tidal marsh sparrows

We estimated mercury exposure and bioaccumulation in sparrow feathers to determine variation among age groups, between sparrow species, and between feather types. Results of feather mercury studies in piscivorous birds indicate that mercury concentrations tend to increase with age and differ between feather types; however, data for insectivorous birds are lacking. We estimated mercury exposure of two insectivorous and sympatric tidal marsh sparrows: coastal plain swamp sparrow (Melospiza georgiana nigrescens), and seaside sparrow (Ammodramous maritimus). Tidal marshes have favorable conditions for mercury methlyation, thus it is likely that tidal marsh sparrows are exposed to methylmercury. We found no difference in mercury concentrations between males and female birds of both species. Adult swamp sparrow feather mercury concentrations did not differ among adult age groups; therefore, mercury was not found to increase with age in sparrows at the site. Hatch-year birds had significantly greater feather mercury concentrations compared with adult birds for both species. Mercury concentrations in adult seaside sparrows were twice as high as those in adult swamp sparrows suggesting species-specific variation, although concentrations in hatch-year sparrow species did not differ. Mercury concentrations differed between feather types in adults of both species. The first primary feather of both species had at least three times greater mercury concentrations than the outer tail feather possibly reflecting varying depuration rates with feather type.