Selenium in Blood of Predatory Birds from Kesterson Reservoir and Other Areas in California

Abstract

Kesterson Reservoir (Merced County, California) is a selenium-contaminated grassland (previously a wetland) that supports a variety of upland birds and other wildlife. Although aquatic birds that occupied a wet Kesterson Reservoir in the early to mid-1980s suffered high mortality and reproductive failure due to selenium exposure, similar effects have not been identified in terrestrial birds. To better characterize selenium exposure and potential effects in terrestrial species, we analyzed blood for selenium concentrations (blood-Se) from predatory bird species at Kesterson and reference areas in California from 1994 to 1998. Except for loggerhead shrikes (Lanius ludovicianus), blood-Se was significantly higher in birds from Kesterson than in birds from other areas. Among species at Kesterson, blood-Se was higher in loggerhead shrikes and northern harriers (Circus cyaneus) than in other species sampled, possibly due to shrikes spending a relatively large proportion of time foraging at Kesterson. In general, data corroborated earlier modeled predictions of selenium accumulation in Kesterson raptors. Calculated (based on blood-Se) but not observed selenium concentrations in eggs of predatory birds from Kesterson exceed a previously established avian toxicity threshold of 10 ppm.