The Ecology of the Wash. I. Distribution and Diet of Wading Birds (Charadrii)

The diet and main feeding areas of the ten most numerous wading birds on the Wash were surveyed during August to May in 1972/73 and 1973/74. The most important prey species were as follows: oystercatcher (Haetnatopus ostralegus)-Cerastodermna edule and Mytilus edulls; knot (Calidris canutus)-Macorna balthica and Cerastoderina; dunlin (Calidris alpina)-Hydrobia ulvae and Nereis diversicolor; redshank (Tringa totanus)-Carcinus rnaenas, Crangon spp. Hydrobia, Nereis and various amphipods; curlew (Numenius arquata)-Carcdnus, Lanice conchilega and several other polychaetes and bivalve molluscs; bar-tailed godwit (Liniosa lapponica)-Lanice, Nereis and Macoma; grey plover (Pluvialis squatarola)-Lanice, other polychaetes, Cerastodernma, Carcinus and Macoma. The diet of the turnstone (Arenaria interpres), ringed plover (Charadrius hiaticula) and sanderling (Crocethia alba) were not studied in detail. In general, the larger waders took the larger individuals of prey species while the smaller waders took smaller prey items. The main feeding areas of oystercatchers, knots, dunlins and bar-tailed godwits coincided with the areas where the density of their main prey species was highest. This was also the case for redshanks, curlews and grey plovers except that there seemed to be some areas of high prey density which were little used. Examples are given of the numbers of each species of wader whose feeding areas would be removed by various proposals to build a reservoir in the south-east corner of the Wash. The effect was very variable between wader species and alternative schemes, but particularly large numbers of knots and dunlins could be affected. The accuracy of the results is evaluated and related to the objectives of the study, which are discussed.