CENTRAL PLACE FORAGING IN OYSTERCATCHERS HAEMATOPUS-OSTRALEGUS - CAN PARENTS THAT TRANSPORT MUSSELS MYTILUS-EDULIS TO THEIR YOUNG PROFIT FROM SIZE SELECTION

Central place foraging (CPF) was studied in eleven pairs of Oystercatc hers Haematopus ostralegus, that transported Mussels Mlytilus edulis t o their young in nesting territories located at varying distances from the shore. None of these pairs showed a strong selection for large Mu ssels. The strategy of sharing the available food optimally between pa rents and young is described in a mathematical model. This model predi cts size selection in any likely situation and is thus rejected. Inste ad, the parents appeared to bring food to their young only after havin g satisfied their own hunger. A second model describing this strategy, predicts that selection for more profitable Mussels has the effect of keeping the parents away from the young for too long in most situatio ns, and hence increases the risk of predation. Only birds transporting prey over large distances were found to select slightly for size wher e they had a wide range of sizes of prey to choose from.