European Black Terns (Chlidonias niger) in trouble: Examples of dietary problems

Black Tern numbers have seriously decreased over most of Europe. Declines have been most severe in western Europe, e.g., in The Netherlands, where a 95% decline has been recorded since the beginning of the century. The causes for this decline likely include loss of safe nesting places and loss of diversity in food organisms (notably large insects) during the chick rearing phase, the latter due to eutrophication of surface waters. Lack of prey diversity leads to an increased risk of temporary absence of suitable prey, which can result in chick starvation. Black Tern chicks cannot develop and mature on insects alone. They may need an additional calcium source, usually fish. In acid waters devoid of fish, calcium deficiency leads to malformation and death in chicks.