Karen C. Drayer Wildlife Health Center

photo: taking blood sample from turkey vulture
Turkey vultures were caught in a baited walk-in trap and a ladder trap. Here, Yvette Hernandez holds a bird while Terra Kelly prepares to draw a blood sample that will be used to determine lead exposure.

WHC Research Explores Influence of Hunting on Lead Exposure in Scavenging Birds

Research findings published in two journal articles in PLoS ONE in 2011 linked lead exposure in turkey vultures to deer and wild pig hunting. The findings showed that a 2008 ban on lead ammunition for big game and non-game hunting activities within the condor range in California reduced lead exposure in turkey vultures and golden eagles.

California went on to pass a bill prohibiting the use of lead ammunition for take of wildlife with a firearm statewide in 2013.

Lead ammunition has been widely used for big game, small game, and non-game hunting in North America, and these two scavenging bird species are at risk of lead exposure when they feed on animals injured or killed by lead ammunition. Lead bullets can produce hundreds of small fragments upon impact which contaminates animal carcasses and discarded viscera that serve as important food sources for scavenging wildlife. 

The first study showed that blood lead concentration in turkey vultures was significantly higher during the deer hunting season compared to the off-season, and blood lead concentration also increased with increasing intensity of wild pig hunting at study sites. 

The second study found that lead exposure in both golden eagles and turkey vultures declined significantly in the first year after the 2008 ban was implemented. While spent lead ammunition in carrion poses a significant risk of lead exposure to scavenging wildlife, our results indicate that the new regulations were sufficient to reduce lead exposure in golden eagles and vultures at our two study sites.

Dr. Terra Kelly, a doctoral student in epidemiology at UC Davis, is primary lead author on both studies and she conducted her research under the direction of Dr. Christine Kreuder Johnson.

A UC Davis press release on this study is available here. See future directions for endangered California condors here.