A6.105 Assemblages of breeding seabirds

Distribution of seabird assemblages

 
Unsurprisingly, the distribution of SPAs identified for important assemblages closely reflects the distribution of major seabird colonies in the UK (Lloyd et al. 1991; Gibbons et al. 1993). There are significant clusters of SPAs in the archipelagos of Shetland and Orkney, as well as the Atlantic islands of St Kilda, the Flannans, North Rona and Sula Sgeir, and Sule Stack and Sule Skerry. Seabird SPAs have been identified along most of the coast of the North Sea, from the far north of Shetland, down the east coast of Scotland, to eastern England (with the Alde-Ore Estuary being the most southerly on this coast). In the south-west, the concentrations of seabirds on the Isles of Scilly and Skomer, Skokholm and Middleholm have been included. Further north, sites are located through the Inner Hebrides to the Minch. One inland colony of seabirds (dominated by gulls) has been identified – Lough Neagh and Lough Beg in Northern Ireland. The sites identified contain a wide range of habitats. Whilst many important seabird colonies occur on cliffs, especially in the north and west of Britain, in other areas seabirds breed on moorland (for example, in Shetland at sites such as Hermaness, Saxa Vord and Valla Field, and Foula), or on soft coastal environments. Several of the English sites include sand dunes and shingle beaches (for example, the Alde-Ore Estuary, the Ribble and Alt Estuaries, and Morecambe Bay). Where low coastal islands, such as the Farne Islands in north-east England, have remained free of land predators, these often hold large numbers of breeding seabirds. There are a wide range of types of cliff, determined by geology and patterns of exposure. These range from hyper-oceanic exposed stacks and islands such as those found at St Kilda, Sule Skerry and Sule Stack in the Atlantic, through to eroded sandstone cliffs, with horizontal bedding planes (such as are found in Orkney at sites such as Marwick Head), and to low cliffs in relatively sheltered areas (for example, the Shiant Isles in Scotland, and Skomer and Skokholm in Wales). The variety of cliff types and locations results in a range of differing assemblages of breeding seabirds.
 

Size of breeding seabird SPAs

 

The largest seabird SPA, by a significant margin, is the St Kilda archipelago, which holds about 600,000 individual breeding seabirds. Other sites holding more than 200,000 individual breeding seabirds during the period of this review are Flamborough Head and Bempton Cliffs (305,784 breeding individuals), East Caithness Cliffs (300,000), Foula (250,000), Handa (200,000), and the Shiant Islands (200,000). In total, all the sites identified under Stage 1.3 for breeding seabirds hold 4,724,078 individual breeding seabirds.