Lead Poisoning of Raptors - A Case Study on Bald Eagles

Bald Eagles (Haliaeetus leucocephalus) is a species of raptor that is widely distributed throughout North America, mainly the United States of America and Canada. Bald eagles have been a symbol of the United States since 1782 and play an important role in the ecosystem as well as being a representation of patriotism. Bald eagles, like many raptors, are opportunistic feeders; they mainly feed on fish, small birds, and mammals but they also frequently scavenge on carrion. Because of their habitat characteristics, feeding habits, and physiological features Bald eagles often come in contact with lead, a heavy metal whose toxicity poses an issue for the wild population of this bird of prey. Bald eagles have been considered as a species that is most affected by lead through anecdotal reports from wildlife rescue centers and for various causes such as habitat, diet, foraging habits, physiological function, and routes of absorption. Literature on North American populations indicate that lead was found in 37% of 294 sick, injured or dead eagles in British Columbia. Out of them, 23% had subclinical exposure and 14% were poisoned, with Canada exhibiting significant lead exposure. In Bald Eagles, lead tends to target the blood, immune function, liver, kidney, bone, and aspects of the digestive system. Poisonings are the leading cause of death at 25% even with acute levels of poisoning, while the survival rate is 5% with elevated concentrations. Ingestion and inhalation of lead are the two most common entry routes. Lead shot, sinkers for fishing, jigs (fishing lures with a molded lead sinker hook), ingesting shot or bullet fragments as grit or in carrion, and uptake from environmental sources (i.e., waste dumps, industrial plants, and sludge from sewage treatment facilities added to agricultural land) are some of the main threats posed to Bald Eagles. To reduce Bald Eagle lead poisoning, it is imperative to consider more proactive solutions such as prohibiting the use of lead bullets, shot, and sinkers through non-toxic alternatives available, but it is also important to make them affordable, accessible, versatile, and to promote sustainable hunting practices. With this in mind, the present thesis aims at providing an overview of lead poisoning in Bald Eagles populations living in North America, trying also to highlight the key points that could serve as a tool to reduce this threat.