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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	The Arctic Skua Stercorarius parasiticus on the Faeroe Islands: Abundance and plumage polymorphism.
Auteurs :	Sven-Axel Bengtson, Auteur ; Dorete Bloch, Auteur
Type de document :	Article
Dans :	Dansk Ornitologisk Forenings Tidsskrift (97(2) 2003)
Article en page(s) :	210-220
Langues:	Anglais
Résumé :	Arctic Skua on the Faeroe Islands were counted in 1981, and based on the counted 1145 pairs the total population was estimated at 1200-1500 pairs. Eighty per cent of the breeding birds were found at below 300m above sea level. They were counted again in 1999-2001 while there is only scattered information for the 1980s and 1990s. In the last 40-50 years, the breeding population varied heavily in some of the largest colonies, and a comparison of populations in 1981 and 2001 in the largest, well-known colonies showed a total decline of 22%. The decrease comes to 45% if one includes the northern part of Suduroy where breeding pairs where numerous in 1981 but neither before nor since have been very many. Smaller colonies have been established in other areas, or in some sites there were scattered isolated pairs. In Svinaskoradalur and on Svinoy and Skuvoy islands, the decrease was largest in 1961-81 but has slowed down since. Possible causes for the decline are changes in food resources, competition with the Great Skua Stercorarius skua, and human persecution. There is no evidence for the latter, but the other two might have played a part, given evidence from sites outside the Faeroes. The ratio of pale to melanic birds decreases from Shetland via the Faeroes to southern Iceland. In the Faeroes, 16.5% of birds were pale in 1981 and 14.6% in 2001. The proportion of pale birds in the large colonies varied between 11 and 17% but was larger for certain other colonies. There is no distinct geographical pattern for plumage polymorphism in the Faeroes, neither has the proportion of pale birds gone down as it was reported from Shetland and Island. In 1930-80, pale birds varied between 2% and 21% in the same colony, but significant variations occurred only in two colonies.

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