Nature Affected by Climate Change

According to the latest scientific findings, climate change is having a profound effect on sheep living in a remote part of the UK.  The scientists’ data shows that, due to warmer temperatures, a certain breed of sheep is shrinking in size – a process that works against the usual pattern of evolution.

Specifically, Soay sheep living on St Kilda – an isolated archipelago within Scotland’s Outer Hebrides – are contracting by 100 grams per annum.  To put this in context, since the mid-1980s these sheep – which are smaller than regular sheep anyway – have become five per cent smaller and five per cent lighter.

Sheep Shrink Effect

The scientists attribute the sheep shrink effect to the warmer temperature being experienced in this part of the world, which are breathing life into lambs that, within the area’s previous microclimate, would have been unlikely to survive.  These smaller lambs, when older, produce smaller lambs yet and so on, and the effect is exacerbated by the weather again, which is bringing lambing season forward and, thus, producing lambs earlier than expected, which are smaller from the outset.

Scottish Sheep

The scientific team studying the Scottish sheep is led by Imperial College London’s Professor Tim Coulson, and, since 1985, they have been analysing sheep trends on 1,500 acre-sized St Kilda – an area where no one has lived since 1930.  Each summer, Professor Coulson and his colleagues have measured the flocks’ size – concluding that, over the past quarter-century, the average weight of an individual sheep has plummeted from 30 kilograms to 28 kilograms. 

“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”, Professor Coulson explained.

“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.”

“Climate change is overriding what we would expect through natural selection”, he concluded, adding that the model observed in St Kilda could be mirrored in other, similar remote parts of the world.  For the Scottish sheep, though, the next stage in the team’s research will involve forecasting what may lie ahead.

“The next step is to extend our description of past change into a predictive model”, Coulson said.  “But it's too early to say if, in 100 years, we will have chihuahuas herding pocket-sized sheep.”

The shrinking Scottish sheep phenomenon features in the current edition of Science journal.

Soay sheep are named after the rock form present in this area and can reaches ages of 16 years.