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Why Are Scottish Sheep Shrinking?

Posted on: Wednesday, 22 July 2009, 13:15 CDT

Experts now suggest climate change as the principal culprit behind a mysterious case of sheep shrinking in size over time, AFP reported.

Two Scottish islands in the remote Outer Hebrides, Soay and Hirta, have only two sole inhabitants: wild sheep that likely arrived there some 4,000 years ago with the first human settlers.

Experts have been studying the impact of weather, food and genetics on a wild animal population using these sheep since the 1950s, due to their isolation and lack of predators.

However, two years ago researchers discovered that the average size of the Soay sheep was progressively shrinking.

The Darwinian evolutionary theory suggests that given the cold, rough winter on the islands, bigger sheep had the better chance of survival, so their genes should progressively dominate the flock.

But scientists at Imperial College London now believe global warming may be reversing this theory.

The researchers say that milder winters in recent decades have enabled smaller lambs, which otherwise would have died after birth, to survive into adulthood and then reproduce.

Australian experts, who have matched weather and population records with the color of the sheep's coats, are now backing the climate change theory.

Gene analysis has shown that the smaller sheep that now dominate the flock are also lighter-haired ones, given that bigger sheep tend to be darker.

In colder times, sheep with darker coats have an advantage, according to Shane Maloney, the lead researcher at the University of Western Australia.

He said mammals with darker coats absorb more solar radiation than their lighter counterparts and thus need to expend less food energy to keep warm.

But this advantage has diminished as the climate has warmed in the North Atlantic, offering more of a chance for lighter-haired (and smaller) rivals in the struggle to survive.

The team said that if environmental effects are the cause of the decline, then they expect the proportion of dark-colored Soay sheep to decrease even further.

The full study was published in the journal Biology Letters.

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On the Net:

• Imperial College London
• University of Western Australia
• Biology Letters
• Image Courtesy Wikimedia

Source: redOrbit Staff & Wire Reports

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