Foraging strategies of Eurasian Oystercatchers (Haematopus ostralegus) on rocky shores: influence of tide, substrate and kleptoparasitism.

Abstract :

We investigated how the foraging strategies and success of limpet-feeding Eurasian Oystercatchers (Haematopus ostralegus) varies with different factors: tide condition, nature of rock, position of limpet and density of potentially kleptoparasitic gulls and conspecifics. The influence of different limpet-opening techniques upon aspects of foraging time were also investigated. Observations were made of oystercatchers on Lundy Island, U.K. using focal animal sampling. A total of 362 limpet attacks were observed (223 successful). Multiple regression analyses revealed that selection of limpet length and handling time were influenced negatively by gull density. Tide was found to influence length of limpets selected and searching and carrying time. Limpet-opening technique influenced opening time only. Binary logistic regression found only limpet length was significant predictor of attack success, with success decreasing as limpet length increased. Oystercatchers appear to forage flexibly, adapting aspects of their foraging strategy in accordance with environmental factors.