Lead exposure in large carnivores in the greater Yellowstone ecosystem

• Main Author: Rogers, Thomas Alan
• Format: Thesis
• Language: unknown
• Published: University of Montana 2010
• Subjects: ammunition; black bear; carnivore; cougars; grizzly bear; lead; scat; wolf; Yellowstone; Canis lupus; Ursus arctos
• Online Access: https://scholarworks.umt.edu/etd/615; https://scholarworks.umt.edu/context/etd/article/1634/viewcontent/Rogers_Tom_Thesis_final.pdf

Exposure to heavy metals is a potential challenge to the conservation of wildlife. One source of heavy metal exposure known to negatively affect avian wildlife is ingestion of lead rifle bullet fragments found in discarded hunter-harvested ungulate gut piles. Some large mammalian carnivores, such as grizzly bears (Ursus arctos), are also known to target these gut piles as a food source while others, such as cougars (Puma concolor), avoid areas with high levels of human hunting pressure. I investigated whether large carnivores in the Greater Yellowstone Ecosystem were exposed to lead, and if so, if ammunition ingested from hunter-harvested gut piles was an apparent source of exposure. I tested samples of blood, tissue, and scat for the presence of lead in black bears (Ursus americanus), wolves (Canis lupus), coyotes (Canis latrans), grizzly bears and cougars. Grizzly bears show higher blood lead levels (n = 82, median=4.4 μg/dL, range 1.1-18.6 μg/dL) than black bears (n = 44, median=1.6, range 0.5-6.9 μg/dL), but blood lead levels did not increase during the autumn hunting season when potentially lead-tainted gut piles are available. Wolves (n = 21) and cougars (n = 8) had lead concentrations near or below the minimum level of detection in both blood and tissue samples. No lead fragments were detected in the scat of grizzly bears, black bears, wolves, and coyotes in samples collected during the summer (n = 209) and fall (n = 214) in 2009. Therefore, unlike avian scavengers, mammalian scavengers do not appear to be ingesting lead ammunition fragments. Grizzly bears do, however, exhibit blood lead levels higher than what is considered safe in humans, but the source of this exposure remains unknown.