Presentation of lead poisoning effects on wildlife and birds of prey and impact on population viability

Abstract

Birds of prey, especially obligatory and occasional scavengers, are at high risk of lead poisoning when they feed on carcasses or prey with embedded lead ammunition in their flesh. Although in many cases, the lead shot or bullet fragments are regurgitated with undigested material such as hair and feathers in the form of pellets, the absorption of lead during food digestion can be enough to kill the raptors. Cases of lead poisoning by shot or bullet ingestion have been described in at least 14 species of diurnal birds of prey and three species of nocturnal raptors in Europe, some of which have endangered or near-threatened populations, such as the White-tailed Eagle (Haliaeetus albicilla), the Spanish Imperial Eagle (Aquila adalberti) or the Bearded vulture (Gypaetus barbatus). In the case of the White-tailed Eagle, lead poisoning has been identified as the cause of mortality in 25% of the studied cases. The Golden Eagle (Aquila chrysaetos) is another of the large eagles with cases of lead poisoning reported in several countries across Europe. Species inhabiting wetlands and feeding on crippled waterfowl, such as the Spanish Imperial Eagle or the Marsh harrier (Circus aeruginosus) were especially at risk before the ban of lead shot adopted in many countries, but there is limited information about the effect of this regulation on birds of prey. All the four vulture species in Europe have shown cases of lead poisoning. High prevalences of elevated blood lead levels are found in the Griffon vulture (Gyps fulvus) in Spain, although other sources apart of lead ammunition may exist. The sedentary population of Egyptian vulture (Neophron percnopterus) of the Canary Islands also suffers an important Pb exposure during the hunting season and some adverse effects on bone mineralization have been associated with bone lead levels. Bearded vulture is another species at risk and its feeding behaviour on the tissue with higher lead level (i.e. bones) can represent an extra risk of exposure to this toxic metal. In addition to the observed mortality, lead can produce adverse effects on the reproduction and the immune function of the sub-lethally exposed birds, so the monitoring studies of the breeding success and mortality of the endangered raptors should consider lead exposure, as well as other toxicants, as drivers of their population dynamics.