Population trends and status of four seabird species (Uria aalge, Alca torda, Larus fuscus, Larus argentatus) at Stora Karlsö in the Baltic Sea

The island of Stora Karlsö hosts the largest colonies of fish-eating seabirds in the Baltic Sea. However, recent and reliable estimates of the number of breeding pairs of the main species have been missing. Based on a complete census in 2014, we estimated the number of Common Guillemots Uria aalge to 15,700 pairs, more than half (up to 70%) of the Baltic Sea population. The number has almost tripled since the early 1970s and the increase has been...