The Treshnish Isles are a central part of the scenery of the southern Hebrides. Like a fleet of Dreadnoughts passing through the Hebrides in line astern, these islands have been landmarks for travellers through the Hebrides for at least 1000 years. The names of some of the islands still reflect their importance to the Vikings who once ruled in the Hebrides. The Treshnish Isles are formed from 8 principal islands varying in size from less than 4 hectares to 60 hectares. The archipelago lies, at its closest, 3km west of Mull and extends along a northeast-southwest axis for a distance of 11km. Apart from the scenery of the Treshnish and their mystique as a group of uninhabited islands, they hold nationally important treasures in the form of a mediaeval castle as well as large colonies of breeding seabirds. In autumn they are the breeding ground of Atlantic grey seals, which give birth to their white pups along their shores. The Treshnish Isles are currently designated as a Site of Special Scientific Interest and are a Special Protection Area under the EC Directive on the Conservation of Wild Birds. The islands provide a breeding habitat for nationally important concentrations of seabirds. At the Harp Rock on the island of Lunga, these are particularly spectacular because dense aggregations of guillemots can be viewed across a narrow but precipitous ravine providing a singular view of a seabird colony. Amongst the fallen rocks on the fossil beaches there are internationally important concentrations of breeding storm petrels. During winter, the islands provide valuable grazing for barnacle geese and, in the autumn, the beaches are breeding habitat for nationally important populations of Atlantic grey seals. In early summer it is also possible to hear the rasping call of corncrakes on Lunga.