Ingested shot in mallards (Anas platyrhynchos) after the regulation of lead shot for hunting in Denmark

Abstract

Since 1986, lead-based gunshot has been banned inter alia for hunting in ponds with the release of mallards (Anas platyrhynchos) in Denmark. To assess whether ingestion of gunshot by this common waterbird has changed as a result of this regulation, we purchased 690 mallard gizzards from ten Danish hunting districts with a program for the rearing and release of mallards for shooting purposes. After X-ray examination, embedded and ingested shot were removed by dissection and subjected to type classification. Of the 690 gizzards, 66 (9.6%) had ingested shot in different combinations of steel, bismuth and lead. The prevalence and occurrence of shot in general were higher than in previous Danish and other studies. However, prevalence of lead shot was markedly lower, and the ingestion of non-lead shot exceeded the levels of ingested lead shot by a factor 10. The result demonstrated that lead shot has become less available over time, although it is still present despite the ban of lead-based ammunition in habitats of released mallards in 1986. Our study proves the hypothesis that mallards have switched from ingesting lead to steel shot due to the change of shot types for hunting in their habitat and indirectly demonstrates that the Danish phase-out of lead shot for hunting has led to decreased levels of waterbird poisoning. No gizzards were detected with embedded lead shot, which demonstrated a full compliance with the lead shot regulation in this sample.