Environmental Contaminants and Cholinesterase in Blood of Vernal Migrant Bald and Golden Eagles in Montana

Abstract

Environmental contaminants typically have the greatest impact on upper trophic level predators such as eagles. We collected whole blood and plasma from 123 migrant bald (Haliacetus leucocephalus) and golden eagles (Aquila chrysaetos) captured between 1985 and 1993 in west-central Montana for analysis of lead (Pb), mercury (Hg), selenium (Se), and organochlorine compounds, and to determine baseline values of cholinesterases (ChE) in free ranging, apparently healthy eagle populations. Elevated concentrations (x = 0.32 ppm) of Pb were detected in 97 percent of bald eagles. Pb was detected in 85 percent of golden eagles but at lower (P<0.05) concentrations (x = 0.18 ppm) than bald eagles. The source of Pb in both species was most likely Pb shot in waterfowl and Pb projectile fragments in ground squirrels (Spennophilusspp.). Hg was detected in 94 percent of bald eagles but only 22 percent of golden eagles. Sources of Hg were most likely fish for bald eagles and fish or gulls (Larus spp.) for golden eagles. Se was detected in 94 percent of bald eagles and in 88 percent of golden eagles. Bald eagles had higher (P<0.05) Se concentrations (x = 0.55 ppm) than golden eagles (x = 0.31 ppm). Aquatic oriented prey were the probable sources of Se for both spedes of eagles. Heavy metal and Se concentrations were not correlated with age or sex in either species. DDE was detected more often in bald eagles (67%) than golden eagles (48%). Organochlorine concentrations were very low and not related to age or sex for either species. Total ChE activity was higher (P=0.0001) in golden eagles than bald eagles. Mean acety/cholinesterase activity was lower ( P< 0.05) in bald than golden eagles (x = 171 vs x = 296), but percent butyrylcholinesterase was higher in bald eagles. Despite fairly pervasive incidence and occasionally high concentrations of potentially toxic contaminants, populations from which both eagle spedes originated appear stable or increasing.