St Kilda is a group of remote Scottish islands lying in the North Atlantic about 70 km west of North Uist in the Outer Hebrides. The St Kilda group consists of the largest island of Hirta, the nearby Dun and Soay, and Boreray with its flanking pinnacles of Stac Lee and Stac an Armin together with some smaller rocky islets. The islands are steep, with precipitous cliffs reaching 430 m on Hirta and 380 m on Soay and Boreray. The vegetation is strongly influenced by sea spray and the presence of seabirds and livestock. Inland on Hirta, species-poor acidic grassland and sub-maritime heaths occupy extensive areas. The islands provide a strategic nesting locality for seabirds that feed in the rich waters to the west of Scotland. The total population of seabirds exceeds 600,000 pairs, making this one of the largest concentrations in the North Atlantic and the largest in the UK. Notable among the many breeding species are auks, petrels and shearwaters, gulls and large proportions of the national and international populations of Gannet Morus bassanus and Puffin Fratercula arctica. These species feed outside the SPA, not only in the waters close to the islands, but also further away in the North Atlantic. It is one of only seven known nesting localities in the EU for Leach's Petrel Oceanodroma leucorhoa.