Abstract: Many shorebirds on their non-breeding grounds feed on macrobenthic fauna which become available at low tide in coastal intertidal flats. All food items have both a cost and benefit per unit of time. Wader species differ in the method used to search for food. This paper presents the results of a study on the feeding behavior, diets and energetic needs of Oystercatchers and Grey plovers in the Bay of Heist, Belgium, using focal bird observations coupled with macrobenthos sampling. The two species of birds differ in their success rate and foraging rate but not in their foraging efficiency. Besides, they were different in the proportion of time spent on different feeding behaviors and activities with most time spent on the Laniche conchlega area. Oystercatchers spent 70.2 % of time for handling mussels and 28.6 % for worms where as 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 of 51.3% and Mussels 23.4 % of Oystercatchers prey and worms 41.2 % of Grey plovers prey. Prey densities of the two species of birds from field observations and benthos sampling were significantly different among the habitats types. The estimated modal length of mussels and worms represent 18% and 33.9% of Oystercatchers prey and 29.1% represented worms eaten by Grey plovers. For both species of birds the overall size of prey estimated (worms R2 = 0.97; mussels, R2 = 0.99) was significantly correlated with the corresponding biomass. In total, Oystercatchers had obtained a total of 158.8KJ daily energy intake from mussels and worms and Grey plovers 2.37KJ from worms. Unlike the observation data, our benthos sample confirmed that MB is the richest habitat of all. Clearly, the most interesting discovery of this study was that, mussels make an important contribution to the total energy intake of Oystercatchers and worms for the grey plovers. Besides, results have indicated the absence of habitat partitioning between the two species of birds.
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