USGS National Wildlife Health Center necropsy and contaminant results for bald and golden eagles collected in 8 States from January 1, 2014, through December 31, 2017 to determine cause of illness/death and lead, mercury, and anticoagulant rodenticide exp

The U.S. Geological Survey National Wildlife Health Center (NWHC) measured environmental contaminants in bald eagles (Haliaeetus leucocephalus) and golden eagles (Aquila chrysaetos) to evaluate dietary exposure to lead, mercury, and anticoagulant rodenticides (AR), which was identified by U.S. Fish and Wildlife Service (USFWS) as a priority issue of concern for the Mountain Prairie Region 6. Carcasses of bald eagles (n = 172) and golden eagles (n = 142) collected from North and South Dakota, Montana, Wyoming, Colorado, Utah, Nebraska, and Kansas between 2014-2017 were assessed for cause of death and liver lead, mercury, and AR levels. Trauma, electrocution, and lead poisoning were the 3 leading causes of death, affecting 51%, 21%, and 20% of eagles, respectively. Trauma was the leading cause of death for both species, while lead poisoning was the second leading cause of death for bald eagles (31%) and was only diagnosed as the cause of death in 7% of golden eagles. Elevated lead levels within the range of subclinical or clinical poisoning (>2 mg/kg wet weight) were present in 25% of eagles tested, including 36% of bald eagles and 11% of golden eagles. No association was detected between lead exposure and trauma, electrocution, or infectious disease. Mercury levels were considered high (>80 mg per kilogram dry weight) for only 2% of bald eagles and no golden eagles. Brodifacoum was the most common AR detected, present in 56% of eagles, including 70% of bald eagles and 39% of golden eagles. However, death was not directly attributed to AR toxicosis in any case.