Abstract from BTO Research Report No 301:

Burton, N.H.K. & Clark, N.A. (2002) (Published 2005)

The numbers and status of waterbirds using Cardiff Bay from 1999/2000 – 2001/2002. A report by the BTO under contract to Cardiff Harbour Authority

1. This report provides a summary of data concerning the numbers and status of waterbirds using wetland habitats within Cardiff Bay since the closure of the Cardiff Bay Barrage. The report thus covers three years - 1999/2000 (November 1999 to March 2000), 2000/01 (April 2000 to March 2001) and 2001/02 (April 2001 to March 2002).

2. Two principal sources of data have been used. BTO counts, undertaken monthly between August and May each year, provide information for 1999/2000, 2000/01 and 2001/02. Wetland Bird Survey (WeBS) data provide further information for 2000/01 and 2001/02. Supplementary information from local and Welsh bird reports is used to complete the species list of waterbirds with the rarer species that have been present in the Bay but that may not have been encountered by the monthly BTO and WeBS counts.

3. Data from all available records show that a minimum of 14 species of wildfowl, 10 waders, 10 gulls, one tern and nine other waterbird species have occurred in Cardiff Bay over the period from November 1999 to March 2002. Information is provided for each of these on peak annual and mean winter numbers using the Bay.

4. Eighteen species were recorded in numbers of 10 or more by BTO and/or WeBS counts and their numbers and status are discussed in greater detail.

5. The present waterbird community of Cardiff Bay is dominated by predominantly freshwater and open water species – primarily grebes, Cormorant Phalacrocorax carbo, Mute Swan Cygnus olor, diving and dabbling ducks and Coot Fulica atra. As a result of its coastal location, the Bay also attracts gulls, particularly towards dusk when the open water is used for roosting. The Bay is additionally still used as a high tide roost site by small numbers of Shelduck and the waders – Dunlin Calidris alpina, Curlew Numenius arquata and Redshank Tringa totanus – that were numerous prior to barrage-closure.

6. Trends in species’ populations could be determined for 15 of the 18 species whose status is discussed in detail. Six of these have shown increases over the last three years: Great Crested Grebe Podiceps cristatus, Mute Swan, Teal Anas crecca, Pochard Aythya ferina, Tufted Duck A. fuligula and Coot. Coot and Pochard were the most numerous of these species, peaks of 110 and 350 respectively being recorded in 2001/02.

7. A further three species had stable populations over the three years: Mallard Anas platyrhynchos, and two fish-eating species – Cormorant and Goosander Mergus merganser.

8. In contrast, populations of Shelduck and five species of wader – Lapwing Vanellus vanellus, Dunlin, Curlew, Redshank and Turnstone Arenaria interpres – which had fallen sharply with the change from estuarine to freshwater conditions associated with barrage-closure, have shown continued declines over the last three years.

9. Three species of gull – Black-headed Gull Larus ridibundus, Lesser Black-backed Gull L. fuscus and Herring Gull L. argentatus – were also numerous at Cardiff Bay over the three year study period.

10. The populations of the majority of the waterbird species using Cardiff Bay are small in comparison to Welsh or British populations. However, Welsh Bird Report data suggest that the numbers of one species, Lesser Black-backed Gull, may be of national importance and, therefore, that Cardiff Bay may be worthy of SSSI or SPA designation.

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