Scotland's wild sheep are shrinking

Wild sheep on a remote Scottish island are shrinking, and scientists blame global warming.

Soay sheep are on average five per cent smaller than 25 years ago, an indication climate change can have a rapid effect on natural populations and a sign of possible more widespread changes in future, according to researchers.

The island of Hirta's shrinking sheep are notable because classical evolutionary theory suggests they should actually get bigger over time, since larger animals tend to be more likely to survive and reproduce than smaller ones.

But now, due to climate change, grass for food is available for more of the year, making survival conditions less challenging, so even slow-growing sheep have a chance of making it and producing smaller offspring in turn.

"It's probably a bit too early to predict that we'll have Chihuahuas running around herding pygmy sheep in say 100 years time," remarked Tim Coulson of Imperial College London, who led the study published in the journal Science.

"In our future work we are going to try and draw these strands together to provide a more comprehensive understanding of the way that climate change is influencing genetic change."