The intertidal zone between land and sea provides some of the most productive and complex of habitats, supporting vast numbers of birds of many species. This chapter explores patterns of use of estuarine mudflats and saltmarshes by birds, drivers of within- and between-estuary variation in use of estuarine resources by these species, and consequences of recent environmental changes on estuaries. A series of case studies of anthropogenic impacts on estuarine habitats and their implications for bird populations is described. Although the primary geographic focus of these examples is western Europe, and particularly Britain, estuaries across the globe are experiencing similar threats and impacts. There are also large intertidal areas outside estuaries that provide rather different environments for birds; these are discussed in Chapter 13.

The estuarine environment and its bird assemblages

Estuarine mudflats and sandflats typically occur in areas of shallow, sheltered tidal water, where currents from rivers and tidal movements slow sufficiently to allow settlement of particles of sediment. Sand and gravel particles are typically large enough to settle out of the water column directly, but the settlement of finer particles of silt and clay is aided by the surface attraction displayed by these fine sediments when in salt water, in a process known as flocculation. The resulting formation of extensive areas of mud and sandflat creates a habitat of extreme importance for many intertidal species and communities (Fig. 12.1).