Cormorants in the Finnish archipelago

Abstract

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