Elemental profiles in feather samples from a mercury-contaminated lake in Central California

Flight feathers from six bird species at Clear Lake, CA were analyzed to determine the extent and distribution of mercury contamination from an abandoned mercury mine and associated levels of 14 other elements. Feather samples were collected from adult and juvenile osprey (Pandion haliaetus), including juvenile osprey from three additional comparison sites; adult western grebes (Aechmophorus occidentalis); adult great blue herons (Ardea herodias); adult mallards (Anas platyrhynchos); adult turkey vultures (Cathanes aura); and juvenile double-crested cormorants (Phalacrocorax auritus). Samples were analyzed by a multielemental x-ray fluorescence method. The osprey from Clear Lake showed significantly elevated mercury concentrations relative to the comparison sites. Different species at Clear Lake had different mercury concentrations based on trophic status; osprey exhibited the highest mercury concentrations and the mallards showed the lowest. Lastly, we quantified differences in elemental concentrations, including mercury, between adult and juvenile osprey from Clear Lake. Elements known to be nutrients, such as sulfur and zinc, did not vary significantly among species or sites. Reproductive success of osprey at Clear Lake was monitored from 1992 to 1996 to determine if osprey reproduction was depressed. During this five-year period, the breeding population grew from 10 to 20 nesting pairs and the average reproductive rate was 1.4 fledglings per nesting attempt. Although the osprey showed the highest mercury levels of any species sampled, their reproduction does not appear to be depressed.