Ardea
Official journal of the Netherlands Ornithologists' Union

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Camphuysen C.J. & Webb A. (1999) Multi-species feeding associations in North Sea seabirds: Jointly exploiting a patchy environment. ARDEA 87 (2): 177-198
We studied the foraging distribution and the formation of multi-species feeding associations of seabirds and marine mammals off the British east coast. The local top-predator community comprised c. 34 species of seabirds, two pinnipeds and eight cetaceans. It appeared that multi-species feeding associations (MSFA's), with rather low species richness and diversity, were commonly formed around fishing vessels, were attracted by or otherwise associated with cetaceans (MSFA's with a generally low but more variable species richness and moderate diversity) and occurred over natural resources, apparently mainly fish shoals (MSFA's with the highest species richness and diversity). Small, short-lived MSFA's were the commoner type, particularly those over natural prey (sandeels and small clupeoids). Black-legged Kittiwakes Rissa tridactyla acted as catalysts in these flocks, Common Guillemots Uria aalge and Razorbills Alca torda as diving producers, apparently driving up fish towards the surface. The specific role of all other species joining in is described in general terms. Typical associations with marine mammals were those in which the cetaceans (mainly White-beaked Dolphins Lagenorhynchus albirostris and Harbour Porpoises Phocoena phocoena) operated as 'beaters' for Northern Gannets Morus bassanus and Black-legged Kittiwakes. The functioning of MSFA's is decribed from two angles. First of all, MSFA's are prominent phenomena on the sea surface, guiding seabirds using visual cues for food finding. Secondly, perhaps more importantly, the differentiation of feeding methods deployed in MSFA's may facilitate sea-birds to reach prey that would otherwise be unavailable for them. It is suggested that the frequent associations of Kittiwakes and auks are the most sustainable system, because commensalism is the underlying mechanism rather than competition. The participation of scroungers in these flocks (Herring Gulls Larus argentatus as common nearshore examples) normally ruined the MSFA formation in no time. Usually, a MSFA would usually collapse as soon as the auks gave up their synchronised feeding activities. This underlines the essential role of Alcidae in these formations. The MSFA's are common and prominent in the North Sea and they deserve further study in the context of when interspecific relationships and the structuring of seabird communities


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