BEIJING, July 3 (Xinhuanet) -- Wild sheep are shrinking on a remote island in Scotland because of climate change, says a U.K. study.

    The scientists studied wild Soay sheep on the remote North Atlantic island of Hirta for nearly quarter of a century. They found that the sheep have shrunk by about 5 percent during the past two decades.

    The law of evolutionary theory says the brown, thick-coated ungulates should have got progressively bigger. Tough winters mean that bigger sheep have a better chance of survival and of reproducing than smaller ones, and eventually they would dominate in the flock's numbers.

    In 2007, the researchers, however, realized that the average size of the Hirta sheep, instead of rising, had been progressively falling.

    The answer, the scientists said Thursday, lies in climate change.

    According to lead researcher, Tim Coulson from Imperial College London: " the team found that the sheep were not growing as fast as they once did and smaller sheep were likelier to survive into adulthood instead of perishing as lambs."

    "This gives smaller sheep a shot at reproduction, which means that the average sheep size has fallen -- by 81 grammes per year (2.85 ounce) per year on average."

    Coulson believes that shorter, milder winters mean that lambs do not need to put on as much weight in the first months of life in order to survive to their first birthday, as they did when winters were colder.

    "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," he said.

    But now, because of climate change, grass for food is available for more months of the year on the island.

    "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," he said.

    The team also found that younger sheep tended to give birth to smaller lambs - a phenomenon they termed "the young mum effect".

    This effect combined with environmental changes had "overridden what we would expect through natural selection".

    (Agencies)