The likely impact of sea level rise on waders (Charadrii) wintering on estuaries

Abstract

Global climate change may affect the internationally important populations of waders (Charadrii) throughout their annual ranges and in a variety of ways. Within Britain, those waders that winter on estuaries are likely to be affected in two principal manners: increasingly mild winter weather already appears to have affected the distributions of the waders within Britain and rising sea level threatens to alter coastal habitats. Wader densities are largely dependent on the availability of their invertebrate prey, which, in turn depends on the nature of the estuarine sediments, itself a function of estuary morphology. Thus changes in estuary morphology, such as might occur with sea level rise, can affect wader density. Models have thus been developed that allow wader densities to be predicted from readily measured aspects of estuary morphology. The MONARCH project used case studies which employed a Geographical Information System, digital elevation models, coastline management plans and sea level rise predictions to simulate incremental increases in sea level for two estuaries. At each increment, values of morphological measurements required by the models were extracted and wader densities were modelled. In both case studies the densities of wader species favouring muddy sediments decreased under management scenarios that allowed land behind existing sea defences to be reclaimed by the sea. However, the models suggest that where changes in estuary morphology were sufficiently large to bring about a decrease in bird densities, generally as a result of increased estuary width leading to sandier sediments the associated increased area more than compensated for the assumed degradation of habitat such that larger numbers could be accommodated overall.