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Key Bird Species on the Thames Estuary

For the purposes of this assessment, key species are defined as those species that are either specifically cited as being internationally important regularly occurring Annex 1 species or migratory species, or which are present in nationally important populations.

Avocet

Avocet is the only Annex 1 waterfowl species for which the Thames Estuary and Marshes SPA is designated and is present in internationally important numbers, so it can arguably be considered to be its single most important component. Within the Thames Estuary, avocet are largely restricted to the lower marine reaches of the river. The mudflats at Higham Bight and Mucking Flats are particularly important for this species and small numbers also breed amongst the saline lagoons at Cliffe (Tidal Thames Habitat Action Plan, 2002). During the five winters between 1995/96 and 1999/00, the Thames was ranked as the third most important estuary for wintering avocets within the UK (Musgrove et al., 2001). In winter 2001/2002, avocets were recorded in nationally important numbers on two occasions and internationally important numbers twice. In March 2002, a record number of 1395 birds was seen (Shaw, 2002). Avocets feed on insects, crustaceans and occasionally small fish and the most recent high water WeBS counts show that over 90% of the SPA population overwinters on Mucking Flats. No WeBS alerts have been triggered for this species.

Black-tailed godwit

Black-tailed godwit
Black-tailed godwit

Black-tailed godwits prefer muddy estuaries where they feed chiefly on intertidal invertebrates, with food located by sight and touch. A wide range of invertebrates is taken, including molluscs, ragworms, crustaceans and earthworms. Within the Thames Estuary, breeding sites are restricted to the Thames Estuary and Marshes SPA and Holehaven Creek, Essex (Tidal Thames Habitat and Species Audit, 2004). A peak of 629 was recorded by Shaw (2002) in November 2001 and WeBS high water counts indicate that around 14% of the SPA population use Mucking Flats. Internationally important numbers of black-tailed godwit also occur within Holehaven Creek, Essex (Tidal Thames Habitat Action Plan, 2002). High increases in the WeBS data have been observed over the short-term (5 years) and long-term (25 years) within the Thames Estuary and Marshes SPA.

Dark-bellied brent goose

The dark-bellied brent goose winters in Britain in internationally important numbers. It breeds in western Siberia and winters in Western Europe, with about half the population in Britain. The species feeds on eelgrass and green algae (especially Enteromorpha and Ulva) which grow on mudflats. Once these food sources are depleted, the birds move inland to feed on coastal arable farmland and pasture. The birds roost on sheltered coastal and estuarine waters (Batten et al., 1990). Benfleet and Southend Marshes SPA is designated for holding 3,819 birds (5 year peak mean 1991/92 – 1995/96) and nationally important numbers overwinter on the Thames Estuary and Marshes SPA. On Benfleet and Southend Marshes SPA high increases in the WeBS counts have been recorded over the medium term (10 years) but medium level decreases have been recorded over the long term (25 years).

Dunlin

Dunlin feed principally in extensive muddy areas of estuaries on a wide range of invertebrate prey, including polychaete worms, gastropod snails, bivalves, crustaceans and occasionally small fish. They are the second most widespread wintering estuarine species in the UK, occurring throughout Britain and Ireland. They are also by far the most numerous species on the Thames Estuary and Marshes SPA, comprising between 37% of the total assemblage. Both this site and Benfleet and Southend Marshes regularly support over 11,000 wintering dunlin (Tidal Thames Habitat and Species Audit, 2004). WeBS alerts have been triggered for this species on both SPAs but they are of no immediate concern as this species is prone to fluctuations (Maclean et al., 2005).

European white-fronted goose

The European white-fronted goose winters in Britain in nationally important numbers. It breeds in western Siberia and winters in Western Europe, with about half the population in Britain. It overwinters in nationally important numbers on the Thames Estuary and Marshes SPA. White-fronted geese forage on farmland for grass, clover, grain and winter wheat. The number of European white-fronted geese over-wintering on the Thames Estuary SPA has decreased sufficiently to trigger a long-term Medium alert. The magnitude of the decline is, however, influenced by uncharacteristically high counts in the late 1960s, since when, numbers have decreased, but not as rapidly as suggested by the alert. The trend contrasts with that of the region, which has fluctuated but generally increased, but is in line with the national trend, with little evidence of a decrease in the proportion of the national WeBS total hosted by this site. Combinations of factors are thus responsible for triggering this alert (Maclean et al., 2005).

Gadwall

The gadwall winters in Britain in internationally and nationally important numbers, predominantly on inshore waters (Batten et al., 1990). The Greater Thames Estuary Natural Area supports at least 5% of the wintering British population (English Nature, 1997). The Lee Valley and Southwest London Waterbodies SPAs, (approximately 20kms upstream from the current study site) are designated for their high numbers of wintering gadwall. Within the study area the species occurs in nationally important numbers at Cliffe Pools. No WeBS alerts have been triggered for this species.

Grey Plover

This is another widespread species within the Thames Estuary and around 34% of the SPA population overwinter on Mucking Flats. Their diet comprises chiefly polychaete worms, molluscs and crustaceans. Nationally important numbers were recorded within the Thames Estuary and Marshes SPA in November 2001, March 2002 and November 2002 (Shaw, 2002). A positive WeBS alert has been triggered for this species on the Thames Estuary and Marshes SPA due to high increases in numbers over the long-term (25 years). However, decreases have been recorded on the Benfleet and Southend Marshes SPA.

Knot

This is the third most numerous estuarine British wader with an average population of 220,000. The mudflats of the Thames estuary are important wintering sites for this species (Batten et al., 1990). Knots are specialist feeders on marine bivalves, particularly Macoma balthica, Mytilus edulis and Cerastoderma sp in the length range 3 - 15 mm. WeBS alerts have been triggered for this species but they are of no immediate concern as this species is prone to fluctuations in numbers (Maclean et al., 2005).

Lapwing

Lapwing are the most numerous estuarine British wader, they forage on saltmarsh for a variety of invertebrates. The highest known winter concentrations of lapwings are found at the Somerset Levels, the Humber and Ribble estuaries, Breydon Water/Berney Marshes, the Wash, and Morecambe Bay. Within the Thames Estuary there is widespread suitable habitat for lapwing in the lower Thames Estuary (UK BAP website). This species occurs in significant numbers throughout the Greater Thames Natural Area (English Nature, 1997). A positive WeBS alert has been triggered for this species on the Thames Estuary and Marshes SPA due to high increases in numbers over the long-term (Maclean et al., 2005).

Little grebe

Little grebe chiefly overwinter on inland freshwater sites (Davidson et al., 1991), approximately 10% overwinter on estuaries and coastal habitats and the Thames estuary is an important wintering site (RSPB). A positive WeBS alert has been triggered for this species on the Thames Estuary and Marshes SPA due to high increases in numbers over the long-term.(Maclean et al., 2005).

Oystercatcher

Wintering oystercatchers are associated with sandy estuaries and cockle and mussel beds. They are widespread throughout Britain with large numbers present on the Thames Estuary. The Greater Thames Estuary Natural Area supports at least 5 per cent of the wintering British population (English Nature, 1997). Medium-level WeBS alerts have been triggered for this species over the short (5 year) and medium-term (10 year) on the Benfleet and Southend Marshes SPA.

Pintail

The Icelandic population of pintail spends the winter in Britain, favouring coastal marshes and estuaries, flooded grassland, lakes and reservoirs. They eat a variety of plants and invertebrates. The Greater Thames Estuary Natural Area supports at least 5 per cent of the wintering British population (English Nature, 1997). Within the study site, Cliffe Pools supports nationally important numbers of pintail (RSPB). A positive WeBS alert has been triggered for this species on the Thames Estuary and Marshes SPA due to high increases in numbers over the long-term.(Maclean et al., 2005).

Redshank

Redshank overwinter in nationally important numbers on the saltmarsh within the Thames Estuary on both of the SPA sites. Additionally, small numbers also breed on the wetter grazing marsh areas adjacent to the Thames in the lower reaches of the estuary (Tidal Thames Habitat Action Plan, 2002). They are known to feed on a variety of invertebrates but typically feed on crustaceans, molluscs and polychaete worms on estuaries. Redshank is mainly a winter and passage-migrant within the Thames Estuary because suitable habitat conditions are limited. A positive WeBS alert has been triggered for this species on the Thames Estuary and Marshes SPA due to high increases in numbers over the long-term.(Maclean et al., 2005).

Ringed plover

Ringed plover are widely distributed along the lower reaches of the river in numbers of international importance. The Thames Estuary and Marshes SPA and Benfleet and Southend Marshes SPA represent nearly 3 per cent of the UK's passage population of ringed plover (Tidal Thames Habitat and Species Audit, 2004). They feed on invertebrates in a variety of intertidal habitats and roost communally, close to feeding sites along the shoreline, on sandbanks or bare arable fields and in low vegetation. Due to uncharacteristically high numbers recorded on the Thames Estuary and Marshes SPA during two winters in the early-1990's, ringed plover have declined sufficiently to trigger a medium-term High-alert. However, apart from these two winters, numbers have remained relatively stable despite regional and national declines (Maclean et al., 2005).

Shelduck

Shelduck has a coastal distribution in Britain, with intertidal sands and mudflats forming the main foraging areas. Its diet includes a variety of invertebrates but predominantly the snail Hydrobia. Breeding shelduck are widely distributed within the tidal Thames where suitable habitat occurs. The Thames Estuary and Marshes SPA supports significant numbers of wintering shelduck. Since the early-1990's, shelduck numbers on the Thames Estuary and Marshes SPA have decreased sufficiently to trigger short and medium term alerts. The latter is of less concern as not only is it lesser in magnitude, but it lies within the range considered normal for this species and cannot be assessed with certainty due to incomplete data. The regional and national WeBS totals have undergone similar declines, with little evidence of consistent decreases in the proportions of the regional and national WeBS totals hosted by this site. This would suggest that large-scale processes are responsible for the downturn in numbers on this SPA (Maclean et al., 2005).

Shoveler

This species winters in Britain on shallow freshwater areas with plentiful marginal reeds or emergent vegetation (Batten et al., 1990). The Thames Estuary is an important area for this species with an average of 300 birds wintering annually, particularly on Cliffe Pools (RSPB). No negative WeBS alerts have been triggered for this species.

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