Food of Eurasian Oystercatcher (Haematopus ostralegus) chicks raised on rocky shores in Southern Norway

Abstract

In the archipelago between Lista and Lindesnes on the southern coast of Norway, we found that Eurasian Oystercatchers, Haematopus ostralegus, chose the prey types that were most abundant within their breeding territories although periwinkles, Littorina littorea, were selected against. This indicates short foraging excursions. The archipelago is divided into three topographical sections that roughly reflect the degree of wave action. Based on differing wave action, food availability for oystercatchers differed in the three sections in the following manner: the inner-section (little wave action) easily available food (sessile blue mussels, Mytilus edulis), the middle-section (intermediate wave action) mixed food availability with a dominance of periwinkles, and the outer-section (much wave action) different prey types dominated by limpets, Patella vulgata. We observed more predation by mink, Mustela vison, in the outer section of the archipelago. The risk of predation from the larger gulls, Larus spp., seemed to be similar throughout the archipelago. Oystercatchers breeding in the inner- and middle-sections were more influenced by human activity and boat traffic than birds in the outer-section of the archipelago. The oystercatchers seemed to adapt to human disturbance thereby improving feeding conditions for both themselves and their offspring.