On the Scottish island of Hirta, the sheep are getting smaller and scientists are pointing the finger at climate change.

The sheep, who have been under close scientific scrutiny since 1985, appear to be shrinking in front of the scientists’ very eyes.

Each year, the female Soay have been losing about three ounces in weight. In all, the average body size of the Soay sheep has decreased by approximately 5 percent over the last quarter-century.

But the sheep aren’t the only thing shrinking on this remote Scottish island in the St. Kilda archipelago. The winter season is also shrinking. Autumns are now longer and spring arrives earlier.

According to the shrinking sheep study recently published in Science, the increasingly short and mild winters over the past 25 years have ensured the sheep now have a year-round supply of grass to eat. As a result, the sheep no longer have to gorge on grass and bulk up during the summer to survive the winter.

At the same time, the average size of the Soay sheep population is being driven down by the “young mum” syndrome. Younger ewes are giving birth to smaller ewes who are surviving due to milder weather conditions.  These smaller ewes will never get as big as the other sheep, a situation that is reducing the average size of the whole population.

Looks like the Soay are shunning classical evolutionary theory that suggests that, within a species, the larger animals are more likely to survive and reproduce than smaller ones. This is evolution for climate change days.

Image: Nick Stenning