Analysis of the Ornithological Interest of the Study Area

The biological richness and productivity of the Thames Estuary is reflected in the number of waterbirds, particularly waders and wildfowl, which it supports. The estuary contains a variety of habitats, which increase the diversity of species that can use it. For example, waders and ducks are dependent on feeding on the benthic invertebrates of mudflats and shallow waters; dark- belied brent geese feed on eelgrass and algae; and an array of diving birds depend on small fish, crustaceans and molluscs sought in the channels at low water and over the mudflats at high water.

The Thames Estuary is of national importance for the populations of twelve species of waterfowl (dunlin, oystercatcher, redshank, black-tailed godwit, lapwing, shoveler, pintail, gadwall, shelduck, European white-fronted goose and little grebe). It is of international importance for the numbers of wintering and passage ringed plover, and wintering dark-bellied brent geese, knot, grey plover and avocet. The total numbers of waders and wildfowl present has at times exceeded 20,000. The importance of the Estuary for waterbirds is reflected in its SPA designations under the Birds Directive. In addition to the SPA designations, the Thames Estuary has been recognised as an internationally important wetland by being designated as Ramsar sites. The ornithological reasons for these designations are similar to the SPA citations.

Other Annex 1 species that regularly occur on the Thames Estuary and Marshes SPA in non-qualifying numbers are breeding common tern, and passage and wintering Bewick’s swan, golden plover, ruff, hen harrier, short-eared owl and kingfisher.

The table below summarises the overall waterbird assemblage of the Thames Estuary and Marshes SPA for the period 1998/99 - 2002/03 and shows the 5 year mean peak for these years. The data presented is only representative of the SPA itself and not the wider area that this review covers, furthermore the data are core counts undertaken at high water and, therefore, do not indicate the use of areas for feeding at low water.

Data provided by the BTO, 2004

The BTO monitor changes in waterbird numbers through a system of alerts based on WeBS data. The alerts system provides a standardised method of identifying the direction and magnitude of changes in numbers at a variety of spatial and temporal scales for a range of waterbird species for which sufficient WeBS data are available. Species that have undergone major changes in numbers can then be flagged by issuing an alert. Alerts are intended to be advisory and, subject to interpretation, should be used as a basis on which to direct research and subsequent conservation efforts if required (Maclean et al, 2005).

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