Diet and foraging behaviour of oystercatchers (Haematopus ostralegus) and grey plovers (Pluvialis squatarola): the importance of intertidal flats

Many shorebirds feed on macrobenthic fauna that become available at low tide in coastal intertidal flats. Waders differ in the method used to search for food. This paper presents results of a study on the feeding behaviour, diet and energetic needs of oystercatchers and grey plovers at the Bay of Heist, Belgium, using focal bird observations and macrobenthos sampling. The two bird species differed in their success rate and foraging rate but not in their foraging efficiency. Oystercatchers spent 70.2 % of time for handling mussels and 28.6 % for worms whereas grey plovers spent 93.3 % of the time for handling worms. During the whole period of observation, 75.5% and 42.5% of prey were identified for oystercatchers and grey plovers, respectively. Of these, polychaete worms comprised 51.3% and mussels 23.4% of oystercatchers prey, and worms 41.2% of grey plovers´ prey. For both species of birds, the overall size of prey estimated was significantly correlated with the corresponding biomass (worms R2 = 0.97; mussels, R2 = 0.99). Oystercatchers obtained a total of 158.8KJ daily energy intake from mussels, worms, and grey plovers 2.37 KJ from worms only. Mussels comprised an important contribution to the total energy intake of oystercatchers and worms for the grey plovers. Habitat partitioning between the two species of birds was not observed.