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St Kilda Soay Sheep Project 

Soay sheep, perhaps the most primitive extant form of domestic sheep, all come from the island of Soay. The origins of the Soay sheep here 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).

Until 1932, when a flock of 107 Soays were rounded up and moved onto Hirta, pure-bred Soays were only found on the island of Soay.

All Soay sheep in the world are descended from those found on the island of Soay in the St Kilda archipelago. These small sheep are one of the most primitive forms of domestic sheep in the world and have probably remained virtually unchanged for thousands of years. No one knows quite when the sheep arrived on St Kilda, but evidence suggests they came with the first human settlers around 4000 years ago. When the Norse arrived at the St Kilda archipelago in the 9th-10th centuries AD they named the island Sauda-ey - 'Island of sheep'.

Until 1932 pure-bred Soays were only found on the island of Soay, then a flock of 107 Soays were rounded up and moved onto the main island of Hirta, Today flocks of Soay sheep are found all over the world.

Today, unmanaged populations of Soays live on both Soay and Hirta where their population fluctuations have interested biologists since the 1950s.

Currently, researchers from from a number of universities and research institutes participate in a multidisciplinary study of factors affecting the population ecology of the sheep in St Kilda. This research has recently been published:
Clutton Brock, T.H. & Pemberton J. (2004) Soay Sheep published by Cambridge University Press. ISBN 0521823005


Running ram
Photograph: Ken Wilson

Recording courtesy of The British Library National Sound Archive

There are several study topics, ranging from investigating the relationship between the Soay population and the Hirta vegetation, to asking why it is that Soays vary genetically with respect to the presence or absence of horns. Each year the lambs in the study area around Village Bay are caught, measured, have blood samples taken and are tagged before release. Once tagged an individual can be identified easily and its progress watched for many years.

Some key results of the project so far are:

  • Populations of sheep on Hirta and Boreray fluctuate in synchrony.
  • Population declines result when high population density combines with poor winter weather, but they are still very difficult to predict.
  • Older, normal-horned rams are most successful reproductively, but (as revealed by DNA profiling) young and polled (hornless) rams also frequently sire lambs.
  • More inbred Soays have lower resistance to nematode parasites (worms) and are less successful reproductively.

Army personnel help to record details of a tagged lamb
Photograph: Davina Graham

Group of rams
Photograph: Ken Wilson

Researchers observing Soay sheep from a distance
Photograph: Ken Wilson

Further Information

Jewell, P.A. et al. 1974 Island Survivors: The Ecology of the Soay Sheep of St Kilda  Athlone Press, London

Clutton-Brock, T.H. et al. 1991 'Persistent instability and population regulation in Soay sheep' Journal of Animal Ecology 60, 593-605

Gulland, F.M.D. 1992 'Epidemiology of nematode parasites in Soay sheep (Ovis aries L.) on St Kilda'  Parasitology 105, 481-492

Illius, A.W. et al. 1995 'Selection for foraging efficiency during a population crash in Soay sheep' Journal of Animal Ecology 64

Soay Sheep Project


© The National Trust for Scotland