The unrivalled grandeur of the St Kilda archipelago is legendary, with its four main islands and several stacs (rocky island pinnacles). These have been described as 'the most majestic sea rocks in existence.' All are known for their precipitous cliffs and thriving sea bird colony - the largest in the northeast Atlantic.
The sea bird colony numbers nearly half a million pairs and includes around a quarter of the world population of northern gannets, the largest European colony of Leach's Petrel and internationally important populations of puffins, guillemots, razorbills fulmars and kittiwakes. St Kilda provides an example of remote island evolution and development in isolation.
Genetic divergence is shown by endemic populations of St Kilda mouse (Apodemus sylvaticus) and the St Kilda wren (Troglodytes troglodytes hirtensis). The archipelago possesses a feral population of Soay sheep, the most primitive domesticated breed in existence, perhaps unchanged since Neolithic times. Man has occupied these barren rocky islands since early prehistoric times. The archaeological remains are testaments to the ability of people to have a sustainable existence in an uncompromisingly hostile environment.