TOWARDS PREDICTING THE EFFECT OF LOSS OF INTERTIDAL FEEDING AREAS ON OVERWINTERING SHOREBIRDS (CHARADRII) AND SHELDUCK (TADORNA-TADORNA) - REFINEMENTS AND TESTS OF A MODEL DEVELOPED FOR THE WASH, EAST ENGLAND

1. The limitations of a model developed in an earlier study to predict the effect of salt-marsh reclamation on shelduck (Tadorna tadorna) an d seven wader species (Charadrii) feeding on the Wash, east England, a re addressed. The model related the numbers of each species feeding do wn-shore of the marsh in a 1-km broad transect to the area of mud or s and present, and thus to the width of the shore itself. 2. Three censu ses of the intertidal feeding grounds were made during the winters of 1989-90. 1990-91 and 1991-92, in addition to one made in 1985-87 on wh ich the earlier model was based, to incorporate annual variations in b ird numbers into the model and to re-affirm the constancy in bird dist ribution. Sediment distribution was determined by satellite image anal ysis, The model was reformulated to include quadratic relationships. 3 . The model was tested both within the Wash and on the Essex coast of east England, Within the Wash. its predictions improved as each year's census was incorporated and as predictions were made for areas of inc reasing size. Outside the Wash, the model predicted the numbers of all species with reasonable precision, suggesting it can be applied over a wider geographical area. 4. It was concluded that the model gives sa tisfactory predictions of how, in general, bird numbers would change i n response to changes in shore width and sediment composition. BY conv erting numbers to percentages, its predictions can be applied to parti cular areas for which the pre-change bird numbers are known. The model may also be applicable to predicting the effect of other changes that directly or indirectly reduce the shore width: for example, barrage c onstruction, sea-level rise and disturbance.