Heavy metal concentrations in Canada geese, snow geese, mallards, and American coots from the northern Rocky Mountains in Montana

Abstract

The presence of metals in migratory bird tissues is well established and mining as an anthropogenic source of exposure to metals is well reported in the scientific literature. Determining the difference between what are hypothesized as normal metal levels and those associated with acute mining toxicity is challenging as spatial and temporal overlap of migratory birds with anthropogenic point sources can be highly variable at individual, population, and species levels. We examined the concentrations of 5 geologically prominent metals and metalloids in the region (arsenic, cadmium, copper, manganese, and zinc) in tissues (kidney, n = 64; liver, n = 65; and muscle, n = 65) from 4 species common to the northern Rocky Mountains in western Montana (Canada goose, Branta canadensis, n = 12; snow goose, Anser caerulescens, n = 15; mallard, Anas platyrhynchos, n = 32; and American coot, Fulica americana, n = 6), to identify metal concentrations for comparison to acute mining‐associated mortalities. Metal levels were highly variable across tissue types for all species. For example, the highest concentrations of copper, manganese, and zinc were measured in the liver (18,300, 3,960, and 38,200, respectively; ug/kg), while cadmium levels were highest in the kidney (973 ug/kg). Among species and tissue types, metal levels were also highly variable. For example, copper levels in mallards were highest in the kidney (6,700 ug/kg) and lowest in muscle (2,780 ug/kg). In contrast, copper levels in American coots were highest in muscle (14,400 ug/kg) and lowest in the kidney (5,060 ug/kg). While the wide variation in metal concentrations among species and tissue types measured in our study can make for difficult comparisons, the results are similar to control cases from other peer‐reviewed publications, and several times lower than dose‐response experiments and incidents in which mining‐associated mortality was known. Our results provide metal concentrations in migratory bird species that utilize the northern Rocky Mountains through Montana, which are essential data for assessing exposure, risk, and mortality associated with anthropogenic activities in the region.