Scottish sheep shrink in the rain

London, UK – Well, we knew about the ice caps, the coral reefs and the ozone layer – and now, apparently, climate change is making sheep shrink as well.

Scotland’s wild breed of Soay sheep is getting smaller, despite the evolutionary benefits of possessing a large body, according to a team led by Professor Tim Coulson from Imperial College London.

Classical evolutionary theory would suggest that over time the sheep would get bigger, because larger animals are more likely to survive and reproduce than smaller ones, and offspring tend to resemble their parents. However, among the Soay sheep of Hirta, a remote Scottish island, average body size has decreased by approximately five per cent over the last 24 years.

The research team analysed body size and life history data, which records the timing of key milestones throughout an individual sheep’s life, for Soays on Hirta over a 24 year period. They found that sheep on the island are not growing as quickly as they once did, and that smaller sheep are living longer.

The researchers believe that, due to climate change, survival conditions are becoming less challenging, with less snow and more rain. This means slower-growing, smaller sheep are more likely to survive the winters than they once were. This, together with the newly-discovered so-called ‘young mum effect’ whereby young ewes produce smaller offspring, explains why the average size of sheep on the island is decreasing.

“In the past, only the big, healthy sheep and large lambs that had piled on weight in their first summer could survive the harsh winters on Hirta,” said Professor Coulson. “But now, due to climate change, grass for food is available for more months of the year, and survival conditions are not so challenging – even the slower growing sheep have a chance of making it, and this means smaller individuals are becoming increasingly prevalent in the population.”

The research is published in Science Express.