The islands of St Kilda have their own unique inhabitants. St Kilda has Soay sheep, Boreray sheep and the St Kilda field mouse. These animals are lesser known than their cousins of the sea and sky, but none the less make for interesting viewing. The Soay sheep in particular are of great conservational interest, and The Scottish National Trust has summer work parties involved in monitoring their breeding and survival patterns. The origins of the Soay sheep are uncertain. The old Scandinavian name Sauda-ey means 'island of sheep', so they were probably present on the island of Soay in Viking times (9th and 10th centuries AD).