Lead-Shot Ingestion by Bald Eagles in Western Arkansas

Abstract

A study was conducted on Holla Bend National Wildlife Refuge, in western Arkansas, to determine the extent to which bald eagles (Haliaeetus leucocephalus) wintering on the area were exposed to lead shot. Waterfowl comprised a significant portion of the diet; 61% of egested bald eagle castings contained waterfowl remains. Lead shot was found in 9 of 31 waterfowl carcasses that provide much of the winter food supply of bald eagles on the refuge. Lead shot was found in 7% of 82 egested castings, indicating that eagles do ingest lead shot in the process of feeding. In recent years, a great deal of interest has been directed toward lead-poisoning as a mortality factor among bald eagles (Haliaeetus leucocephalus; Pattee and Hennes, 1983; Feierabend and Myers, 1984). It has long been recognized that large numbers of waterfowl succumb annually to lead (Bellrose, 1975). How- ever, only recently has there been an attempt to compile and analyze information on the extent to which lead may affect bald eagles feeding on dead or crippled waterfowl. Feierabend and Myers (1984) reported that: 1) a growing body of evidence suggests that significant numbers of bald eagles die annually from lead- poisoning; 2) a minimum of 77 bald eagles died of lead-poisoning between 1966 and 1984; and 3) these data probably under-estimated the actual extent of the problem as most eagle carcasses are never recovered. Bald eagles are particularly vulnerable because population levels are low and because they readily feed on dead or crippled prey, particularly waterfowl (Pattee and Hennes, 1983). Arkansas is one of 27 states with documented cases of bald eagle mortality due to lead poisoning (Feierabend and Myers, 1984). Holla Bend National Wildlife Refuge, Pope Co., Arkansas, is a major wintering area for bald eagles and waterfowl and has had documented cases of lead poisoning in waterfowl. Therefore, the report by Feierabend and Myers (1984) listed Pope Co. as one of 89 counties nationwide where there is a high risk of bald eagles being poisoned by lead after ingesting lead pellets present in dead or crippled waterfowl. While there was a clear potential for poisoning of eagles wintering on Holla Bend, no quantitative data were available for assessing the extent to which eagles were actually exposed to lead shot. This report summarizes the results of a study conducted on Holla Bend during the winter of 1985-1986 to evaluate the extent to which wintering bald eagles were exposed to lead shot. The objectives of the study were to: 1) determine the frequency of occurrence of waterfowl in the diet of wintering bald eagles using the area; 2) evaluate the extent of lead shot in waterfowl carcasses on the area; and 3) determine the frequency of occurrence of lead shot in egested castings produced by bald eagles using Holla Bend.