The impact of lead poisoning from ammunition sources on raptor populations in Europe.

Abstract

Poisoning caused by ingestion of spent lead (Pb) ammunition in food items is a common cause of death of raptors. However, there has been no previous attempt to assess the impact of lead poisoning on populations of raptors throughout Europe or examine how this relates to the prevalence of hunting. We used measurements of lead concentration in the liver from over 3000 raptors of 22 species found dead or dying in the wild in 13 countries and a lead poisoning threshold of 20 ppm (dry weight) to assess the proportion of these in which lead poisoning caused or contributed to death. The prevalence of lead poisoning as a cause of death of raptors varied substantially among European countries and was positively correlated across countries with the reported number of hunters per unit area. Ten species had a non-zero proportion of individuals with concentrations exceeding the lead poisoning threshold ranging between 0.3% and 16.5%. The estimated annual conditional death rate from lead poisoning for these ten species averaged 0.44% (range 0.06-0.85%). Scavenging species feeding regularly on carcasses of game animals,tended to have a high annual probability of death from lead poisoning. So too did some predators which only sometimes scavenge, but prey on frequently hunted birds, such as gamebirds, waterfowl and pigeons, which may contain ingested or embedded lead shot. Small-bodied predators had a low annual probability of death from lead poisoning. Modelling indicated that European populations of adult raptors of the ten focal species averaged 6.0% smaller (range 0.2-14.4%) than they would be without the effects of lead poisoning. A given rate of lead poisoning mortality resulted in greater expected population reductions for species with high annual survival rate and late age at first breeding.