Dynamics of Protected Bird Communities in a Finnish Archipelago

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Abstract
Four types of islands, which form a primary succession sere, have characteristic coastal bird communities (Anseriformes and Charadriiformes) on the Krunnit Islands (North Gulf of Bothnia, 65.degree. 25'' north, 25.degree. 00'' east). Recovery of the communities started after the island group was protected in 1936. Bird populations were censused in 20 breeding seasons from 1939-1972. The main changes observed were the increase of gull populations and related changes in the distribution of duck populations. Protection conferred a great advantage for the large gulls, but the effect was negligible on the wader populations. Species diversity on the 4 island types differed consistently throughout the study period. Diversity increased with the successional stage of an island. Protection caused a decrease of species diversity, because the re-established gull and tern populations now dominate in the communities. Thus, high species diversity does not always indicate a high conservation value of a bird community. Recovery of the communities altered the relationship between island area and the number of species on small islands. Rates of species turnover in the island group were of the order of 0.01 species/yr. Calculations indicated that these northern islands are very rapidly.sbd.in less than 10 years.sbd.saturated with coastal bird species.

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