Lead exposure and food processing in white-tailed eagles and other scavengers: an experimental approach to simulate lead uptake at shot mammalian carcasses

Abstract

A serious hazard for avian scavengers is lead poisoning caused by feeding on shot mammalian carcasses containing fragments of lead-based bullets. Both obligate and facultative scavenging species are affected, such as the white-tailed eagle Haliaeetus albicilla for which lead intoxication is a major source of mortality. However, the exploitation of hunter-killed carrion by facultative avian scavenger communities is little studied. As bullet fragments recovered from the intestinal tract of white-tailed eagles were generally small and did not represent the full spectrum of available bullet fragment sizes, the hypothesis arose that this is the result of selective food processing in that eagles avoid the intake of large metal particles. Here, we used an experimental approach to identify lead-exposed species and explore the food processing of white-tailed eagles and other scavengers. We conducted feeding experiments with free-ranging scavengers in six eagle home ranges in northeastern Germany and with six eagles temporarily held in captivity. We provided ungulate carcasses containing non-toxic iron particles of different diameters, simulating bullet fragments, as food source. Primarily, avian scavengers such as ravens, eagles and buzzards exploited the carcasses, indicating them to be exposed to lead fragments and poisoning. With increasing diameter of experimental particles, free-ranging scavengers and captive eagles increased the percentage of particles avoided during feeding. Scavengers almost completely avoided fragments of 8.8 mm diameter. Behavioural observations of captive eagles showed that they detected iron particles predominantly by touching the experimental carcass with their bill tip, suggesting that they use mechanoreceptors to judge food quality. Our findings indicate that the use of bullets that deform or fragment into particles greater than 9 mm in size, such as numerous lead-free bullets, may prevent metal ingestion and poisoning in avian scavengers.