Lead exposure in large carnivores in the greater Yellowstone ecosystem

Ingestion of lead rifle bullet fragments found in discarded hunter-harvested ungulate gut piles negatively affects avian wildlife. Some large carnivores, such as grizzly bears, are also known to target these gut piles as a food source and are therefore potentially at risk of lead exposure. We investigated whether large carnivores in the greater Yellowstone ecosystem were exposed to lead, and if so, if ammunition ingested from gut piles was an apparent source of exposure. Grizzly bears (Ursus arctos, n=82) exhibited higher blood lead levels (median=4.4μg/dL, range 1.1-18.6μg/dL) than black bears (Ursus americanus, n=35, median=1.6, range 0.5-6.9μg/dL), but blood lead levels did not increase during the autumn hunting season when potentially lead-tainted gut piles are available. Wolves (Canis lupus, n=21) and cougars (Puma concolor, n=8) showed lead concentrations near or below the minimum level of detection in both blood and tissue samples. Unlike findings in previous studies on avian scavengers, we did not find lead ammunition fragments to be a widespread source of lead exposure in large carnivores. Grizzly bears do, however, exhibit blood lead levels that are higher than what is considered safe in humans, but the source of this exposure remains unknown.