St Kilda (Scottish Gaelic: Hiort) is an isolated archipelago 64 kilometres (40 mi) west-northwest of North Uist in the North Atlantic Ocean. It contains the westernmost islands of the Outer Hebrides of Scotland. The largest island is Hirta, whose sea cliffs are the highest in the United Kingdom and three other islands (Dùn, Soay and Boreray), were also used for grazing and seabird hunting. The islands are administratively a part of the Comhairle nan Eilean Siar local authority area.
St Kilda may have been permanently inhabited for at least two millennia, the population probably never exceeding 180 (and certainly no more than 100 after 1851). The entire population was evacuated from Hirta (the only inhabited island) in 1930. Currently, the only year-round residents are defence personnel although a variety of conservation workers, volunteers and scientists spend time there in the summer months. The entire archipelago is owned by the National Trust for Scotland. It became one of Scotland's five World Heritage Sites in 1986 and is one of the few in the world to hold joint status for its natural and cultural qualities.
Two different early sheep types have survived on these remote islands, the Soay, a Neolithic type, and the Boreray, an Iron Age type. The islands are a breeding ground for many important seabird species including Northern Gannets, Atlantic Puffins, and Northern Fulmars. The St Kilda Wren and St Kilda Field Mouse are endemic subspecies. Parties of volunteers work on the islands in the summer to restore the many ruined buildings that the native St Kildans left behind. They share the island with a small military base established in 1957.
St Kilda is a breeding ground for many important seabird species. The world's largest colony of Northern Gannets, totalling 30,000 pairs, amount to 24 percent of the global population. There are 49,000 breeding pairs of Leach's Petrels, up to 90 percent of the European population; 136,000 pairs of Atlantic Puffins, about 30 percent of the UK total breeding population, and 67,000 Northern Fulmar pairs, about 13 percent of the UK total. Dùn is home to the largest colony of Fulmars in Britain.
Prior to 1828, St Kilda was their only UK breeding ground, but they have since spread and established colonies elsewhere, such as Fowlsheugh. The last Great Auk (Pinguinus impennis) seen in Britain was killed on Stac an Armin in July 1840. Unusual behaviour by St Kilda's Bonxies was recorded in 2007 during research into recent falls in the Leach's Petrel population. Using night vision gear, ecologists observed the skuas hunting petrels at night, a remarkable strategy for a seabird.
Numerous factors led to the evacuation of St Kilda. The islands' inhabitants had existed for centuries in relative isolation until tourism and the presence of the military in World War I induced the islanders to seek alternatives to privations they routinely suffered. The changes made to the island by visitors in the nineteenth century disconnected the islanders from the way of life that had allowed their forebears to survive in this unique environment. Despite construction of a small jetty in 1902, the islands remained at the weather's mercy.
On his death on 14 August 1956, the Marquess of Bute's will bequeathed the archipelago to the National Trust for Scotland provided they accepted the offer within six months. After much soul-searching, the Executive Committee agreed to do so in January 1957. The slow renovation and conservation of the village began, much of it undertaken by summer volunteer work parties. In addition, scientific research began on the feral Soay sheep population and other aspects of the natural environment. In 1957 the area was designated a National Nature Reserve.
In 1986 the islands became the first place in Scotland to be inscribed as a UNESCO World Heritage Site, for its terrestrial natural features. In 2004, the WHS was extended to include a large amount of the surrounding marine features as well as the islands themselves. In 2005 St Kilda became one of only two dozen global locations to be awarded mixed World Heritage Status for both 'natural' and 'cultural' significance. The islands share this honour with internationally important sites such as Machu Picchu in Peru, Mount Athos in Greece and the Ukhahlamba/Drakensberg Park in South Africa.
The St Kilda World Heritage Site covers a total area of 24,201.4 hectares (59,803 acres) including the land and sea. The land area is 854.6 hectares (2,112 acres). St Kilda is a Scheduled Ancient Monument, a National Scenic Area, a Site of Special Scientific Interest, and a European Union Special Protection Area. Visiting yachts may find shelter in Village Bay, but those wishing to land are told to contact the National Trust for Scotland in advance. Concern exists about the introduction of non-native animal and plant species into such a fragile environment.
The oldest structures on St Kilda are the most enigmatic. Large sheepfolds lie inland from the existing village at An Lag Bho'n Tuath (English: the hollow in the north) and contain curious 'boat-shaped' stone rings, or 'settings'. Soil samples suggest a date of 1850 BC, but they are unique to St Kilda, and their purpose is unknown. In Gleann Mòr, (north-west of Village Bay beyond Hirta's central ridge), there are 20 'horned structures', essentially ruined buildings with a main court measuring about 3 by 3 metres (10 by 10 ft), two or more smaller cells and a forecourt formed by two curved or horn-shaped walls.