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2. Introduction

One of the fundamental paradoxes the management of estuaries has to cope with is the fact that most of the major estuaries in the world are to some degree modified by Man, yet, in many countries, these systems include more nature protected areas than any other habitat (McLusky & Elliott 2004). Estuaries supply mankind with extensive economic goods and services, by providing, for example, fish and shellfish, aggregates for building, and water for abstraction. As such, several anthropogenic pressures concentrate in these areas. Also, estuarine areas are often designated under a series of European directives and conventions for their international importance as habitats for waterbirds populations (e.g. European Habitat and Species Directive, Bird Directive, Ramsar convention) and several conflicts may arise between the use of estuarine areas (and the resulting impacts on the natural environment) and their conservation as bird habitats. The understanding of the critical determinants of bird usage of estuarine habitats is therefore an important element to inform the management of these areas towards a reduction (through mitigation or compensation) of these conflicts/impacts.

The distribution of waterbirds in estuarine habitats and the identification of the main factors affecting bird habitat use has been investigated within the TIDE project. This knowledge will provide broad guidance for the management of these complex systems, e.g. by directing mitigation programmes towards the provision of better habitats for bird species.

The study focussed on three of the four TIDE estuaries, the Elbe (D), Weser (D), and Humber (UK). These estuaries share similar broad characteristics (e.g. they have a strong tidal influence, important port areas) and most of their area is protected under a series of designations. The Humber Estuary has been designated under the Species and Habitats Directives and is a Natura 2000 site. Underpinning this European level designation is a UK legal framework based around Sites of Special Scientific Interest (SSSIs). The mouth of the Weser and Elbe rivers is part of the International Wadden Sea system, the world’s largest intertidal wetland, designated as a UNESCO World Heritage site, Natura 2000 site and a site of national importance under the Ramsar convention. In particular, Special Protected Areas contributing to the Natura 2000 network in the Elbe estuary cover about 90% of the estuary’s water and foreshore surface areas, with more than 90% of the tidal Weser surface area and floodplains also belonging to the EU‘s Natura 2000 network of protected areas. The mosaics of tidal habitats present in these systems (e.g. mudflats, salt marshes, shallow water areas), in fact, provide important roosting and feeding habitats for several migratory waterbird species. Besides these common broad characteristics, the three estuaries present a different distribution of the pressures and habitats along the estuarine continuum which might affect the bird habitat use in different ways, leading to different results obtained for the different estuaries.

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