The Food Requirements and Ecological Relationships of a Seabird Community in North Norway

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Abstract
Almost all species of seabirds at Hornoy and Reinoy are increasing in numbers. The Herring Gull colony is one of the largest in Europe. Most species feed mainly on capelin, but sandeels are important for Brunnich''s Guillemots, Razorbills and Shags. Diets remained closely similar from year to year but consistently differed between species. Puffins and Razorbills fed largely on immature fish while other species took mostly two year old fish. The majority of the two year old capelin consumed by auks in June and July were ripe, although most capelin spawn in March and April. Foraging ranges extremely short, breeding success and chick growth rates unusually high. Food consumption totalled 9000 tonnes yr-1, of which 7500 tonnes were capelin. Food appeared to be superabundant, and dietery differences between species probably reflect anatomical and behavioural adaptations rather than niche partitioning through active competition. Seabirds appear to select capelin of high lipid content since they fed predominantly on ripe two year old fish during chick-rearing, when spent fish were of poorer nutritional value.