Mercury Contamination of Canadian Prairie Seed Eaters and their Avian Predators

Abstract

The investigation revealed that mercury contamination is rather widespread in prairie wildlife.Livers of seed-eaters shot on fields sown with treated grain contained significantly higher mercury levels than those shot on untreated fields, strongly suggesting mercury seed dressings as the major source of contamination.This suggestion is supported by mercury concentrations both in seed-eaters and in their avian predators being significantly higher in specimens from Alberta, where the use of mercury seed dressings is widespread, than in Saskatchewan where seed treatment is much less common.There was considerable variation in mercury levels between and within species.Among seed-eating birds, the highest residue levels were found in pheasants.Lesser, but still considerable mercury concentrations were shown in partridges and small seed-eating passerine birds such as Horned Larks.Among the rodents, ground squirrels inhabiting treated fields were shown to have high mercury levels.Eggs of the predominantly bird-eating falcons and accipiters were frequently found with elevated mercury levels while the levels in eggs of those eagles, buteos, and harriers which prey largely on rodents were low.This difference can be explained satisfactorily on the basis of their food habits since mercury levels were higher in principal bird prey species than in rodents.Reproduction in falcons and accipiters may be adversely affected since their eggs frequently carried mercury levels comparable to those shown experimentally to reduce hatchability in pheasant eggs.This suggests that mercury is contributing to the recently documented organochlorine-related population declines.