Cormorants in the Finnish archipelago

The Great Cormorant Phalacrocorax carbo sinensis started to breed in Finland in 1996following rapid growth of the population in western Europe. The Finnish population increasedvery quickly in nine years from 10 pairs to 2,930 pairs in 2004. The growth of thebreeding population and the spatial pattern of colonization and possible factors affectingit in Finland are discussed. Breeding success was studied in detail within a single colonyon the southern coast of Finland. Breeding successwas higher in central nests of the studycolony than in nests at the edge of the colony. Survival rates of eggs and 0-5 day-oldyoung were lower than older young (>5 days old). Fledging success was determined in anumber of different sized colonies, and was highest in large colonies. Small colony sizemay reduce the reproductive output, because (1) small colonies could have a relativelylarge proportion of young and inexperienced breeders and (2) small colonies may haveproportionally more edge nests than large colonies and therefore suffer relatively morefrom negative edge effects.

Aleksi Lehikoinen, Ornis Fennica 83:34-46. 2006