Status of Caspian Terns Sterna caspia in the Baltic

Abstract

An interbaltic census made in Finland, Sweden and the Estonian SSR, in the summer of 1984, revealed that the Caspian Tern population in the Baltic Sea had decreased by a quarter since the early 1970s. These countries share the whole Baltic population at present. In Finland and Sweden, the population had decreased by about 30% and a slight decrease in mean colony size was also noted. In Estonia, the population had remained stable or even increased slightly . The reasons for these changes are largely unknown. Ring recovery data give certain evidence of a higher mortality rate on the wintering grounds during dry years. There is an urgent need for up-to-date population studies in the Baltic in order to assess the reasons for the population changes.