SEARCHING BEHAVIOR AND DIET OF OYSTERCATCHER HAEMATOPUS-OSTRALEGUS PAIRS FEEDING IN THEIR TERRITORIES

Search path, searching behaviour and diet of pairs of Oystercatchers f eeding in mudflat territories were studied during spring. females ate Nereis, Mya, small unidentified prey, probably Corophium, and a few Ma coma, whereas males primarily ate Macoma. Even when female and male fo raged in the same site, they often caught different prey. The combinat ion of 'The Search-rate/Detection Model' (Gendron & Staddon 1983) and 'The Harvestable Prey Model' (Zwarts & Wanink 1993) provide the theore tical framework in which to explain these differences in diet. Macoma are thought to be more cryptic than Nereis, Mya and Corophium. Therefo re females, while searching at a faster rate than their respective mat es, caught far fewer cryptic prey, but a greater number of more conspi cuous prey than their mates. On the basis of distances moved before an d after capturing prey, males exhibited area-restricted searching for Macoma and Corophium. In contrast, females did not exhibit any area-re stricted searching. it is suggested that the distribution of Macoma an d Corophium available to males searching slowly was more clumped than that of these two prey species available to females searching more qui ckly.