The influence of human activity on the breeding success of Eurasian Oystercatchers Haematopus ostralegus in southern Norway

Breeding Eurasian Oystercatchers Haematopus ostralegus on islands of southern Norway experience different levels of human disturbance in addition to different environmental factors within the archipelago. The purpose of this study was to determine whether different levels of human disturbance influenced breeding success, specifically fledging success. As expected, breeding attempts in areas with no human disturbance were the most successful, and breeding attempts in areas with boat traffic, mooring and people going ashore were the least successful in producing fledglings. Nesting near gull colonies did not seem to influence fledging success. The inner-section of the archipelago (where most people live) had a greater number of nesting pairs that produced a greater number of fledglings than pairs breeding in the outer section of the archipelago. Pairs breeding in the middle section of the archipelago had the lowest fledging success. This study suggests that on the southern coast of Norway the number of Eurasian Oystercatcher breeding attempts in the outer section of the archipelago is limited by larger wave action and relatively lower food availability than in the other sections. The inner section of the archipelago has more favourable environmental conditions, and breeding Eurasian Oystercatchers seem to be habituated to nonthreatening human disturbance there, thus enabling them to produce more fledglings than in any other section. Human activity, especially people going ashore from boats, may be the greatest limiting factor to breeding success in the middle section of the archipelago.