Metal levels in feathers can often be used as an indicator of exposure and of potential effects in birds. In previous work at Agassiz National Wildlife Refuge, northwestern Minnesota, pied-billed grebe (Podilymbus podiceps) eggs had significantly higher levels of manganese and mercury and significantly lower levels of selenium than eared (Podiceps nigricollis) or red-necked grebes (Podiceps grisegena), but in 1999, pied-billed grebes had significantly higher levels of mercury, but lower levels of selenium and tin than the other grebes. This led us to examine whether these patterns held up in feathers of grebes as a function of age. The feathers of young birds represent local exposure. We collected feathers of flightless young and adult grebes from 1997 to 1999 in the marshes at Agassiz National Wildlife Refuge. Regression models indicated that year, age, or species were significant factors accounting for variations in the levels of arsenic, cadmium, chromium, lead, manganese, mercury, and selenium, depending on the metal. Overall, there were significant intraspecific differences for all metals. Pied-billed grebes had the highest levels of arsenic, chromium, and selenium, and eared grebes had the highest levels of cadmium, manganese, and mercury. Pied-billed and western grebes (Aechmophorus occidentalis) had the highest levels of lead. There were significant age-related differences in cadmium, chromium, and mercury for both eared and red-necked grebes, for arsenic in eared grebes, and for lead and manganese in red-necked grebes. Adults had higher levels of all metals, except young had higher levels of chromium. Mercury in the feathers of eared grebes were higher than found from other studies with a wide range of aquatic and marine birds and were above those known to cause adverse effects in laboratory studies, suggesting some cause for concern.
