Verspreiding, voedsel en fourageergedrag van de Ivoormeeuw Pagophila eburnea rond West-Spitsbergen

The Svalbard archipelago was visited every summer during 1985-1990. The distribution of sightings of Ivory Gulls at sea and during landings around West-Spitsbergen, as shown in figures 1 and 2, is discussed. Ivory Gulls were encountered 61 times, including 110 adult individuals. Most Ivory Gulls were observed near human settlements (31.8%, n= 110), along glacier fronts (31.8%) or flying by (15.4%). Several gulls were encountered near freshly killed prey of Polar Bear Ursus maritimus (6.4%) or flying along ice edges in fjords (5.5%). Tourist visits in Agardhbukta (figure 1, nr. 41) attracted several Ivory Gulls which were begging for food (9.1%). When corrected for observer effort (figure 2), it was found that besides a local concentration at Agardhbukta/Negribreen (east coast), north and northeast West-Spitsbergen were the principal regions for Ivory Gulls. The lack of sightings in the NW and around Hornsund leads to the suggestion that several colonies, indicated on maps drawn by Løvenskiold 1984 (slightly modified by Birkenmajer 1969, Blomqvist & Melander 1981, Cramp & Simmons 1983, and Norderhaug 1989), are no longer existing. Ivory Gulls were not seen on the open sea, west and southwest of West-Spitsbergen (cf. Mehlum 1989b). Ivory Gulls were seen foraging on a variety of food sources, including Polar Bear kills, drying corpses of Ringed Seals Phoca hispida at a trapper’s cabin, zooplankton welling up along the beach and near glacier fronts (Chaetognatha (Sagitta elegans), and crustacea (Parathemisto spp., Gammariidae)), on stranded crustaceans on a mud flat in Wijdefjorden (Parathemisto libellula, Gammariidae), on a rubbish tip and in dirty water of Longyearbyen’s sewer pipe. Its apparent reluctance to settle on water (Ivory Gulls fed by hovering and contact dipping) made it an inefficient marine feeder compared to Kittiwakes Rissa tridactyla. However, fish and zooplankton appear to be important items in its diet (Bateson & Plowright 1959, Divoky 1976), apparently mainly obtained by hovering over water and walking on ice edges, but also by plunge-diving (Mehlum 1989b). The competition at Polar Bear kills among Ivory Gulls, Glaucous Gulls Larus hyperboreus, Great Skua Catharacta skua and Arctic Skuas Stercorarius parasiticus led to a dominance hierarchy. Ivory Gulls were clearly dominant and obtained their share first. Remarkably, but unexplained, was the scared behaviour of the much bigger Glaucous Gulls when an Ivory Gull came close.