Lead from Spent Ammunition: a Source of Exposure and Poisoning in Bald Eagles

Abstract

Ongoing occurrence of elevated levels of lead in bald eagles (Haliaeetus leucocephalus) following the ban on lead shot for waterfowl hunting led us to hypothesize that spent lead from ammunition, which is present in field residues of white-tailed deer (Odocoileus virginianus), represented a source of lead exposure in eagles. We conducted a case-control study using data from 1,277 bald eagles admitted for rehabilitation from January 1996 through December 2009. A multivariate logistic regression model was used to predict the odds of elevated lead levels using admission date in relation to deer hunting season, recovery location in relation to deer hunting zones, and age as predictors. We also assessed mean liver copper concentrations from eagles with elevated lead levels and from eagles with background lead levels, because most high velocity rifl e bullets that are used for deer hunting are jacketed in copper. We found 334 bald eagles with elevated lead levels out of 1,277 bald eagles we examined. We detected significantly increased odds for elevated lead levels based on season (late fall and early winter), deer hunting rifle zone, and age (adult birds). The mean liver copper concentration was higher (P = 0.02) in eagles with elevated lead levels. These combined results supported our hypothesis that eagles are acquiring lead from hunter-shot deer. Further research is needed to determine whether this exposure to lead is having a population-level impact.

Keywords

• ammunition
• bald eagles
• copper
• human–wildlife conflicts
• lead
• poisoning
• white-tailed deer