Comparison of lead contamination among related scavenging birds sharing food sources: a call for caution when using surrogate species

摘要

Lead contamination is a global problem affecting a large number of bird species around the world. Among the different avian guilds, vultures and facultative scavengers are particularly threatened by this toxic metal. However, little information is available about differences in exposure to this metal for sympatric vulture species that share food resources. We compared blood lead concentrations of two closely related sympatric obligate scavenger species, the abundant Black Vulture Coragyps atratus and the threatened Andean Condor Vultur gryphus in north-western Patagonia, Argentina. We sampled 28 Andean Condors and 29 Black Vultures trapped foraging in the same area in the steppe. We also sampled 16 Black Vultures foraging in a rubbish dump to determine whether there were differences in lead contamination among foraging sites. Andean Condors had significantly higher mean blood lead concentrations than Black Vultures. There was no difference in lead concentrations between Black Vultures trapped in the steppe and in the rubbish dump. The prevalence and probability of lead concentrations above the threshold level (20 mu g/dL) was higher for Andean Condors than for Black Vultures, potentially producing different effects on their health. This disparity in lead contamination may be due to differences in their foraging habits or in their susceptibility to this toxic metal. Overall, our results suggest caution in using an abundant surrogate species to infer lead contamination in a closely related but harder to sample species.