A warmer St Kilda could be changing the fate of its famous sheep

placeholder image — St Kilda's Soay sheep | IanStevenson

The population of Soay Sheep on St Kilda has historically been volatile - but now long-term patterns in numbers are now being detected by researchers

Britain’s most remote sheep may be among the unlikely beneficiaries of climate change, with their often volatile population appearing to stabilise as a warmer St Kilda produces more food, researchers have said.

The flock of Soay sheep on the westerly outlier of the Outer Hebrides has historically been marked by dramatic rises and falls in numbers. The harsh winters can bring a sudden wave of deaths as the animals struggle to find enough food, sometimes causing substantial declines in the population. Winter weather and infection with parasites also have an impact on winter survival and sheep numbers.

However researchers behind the Soay Sheep Project, which has been ongoing since the 1980s, said mortality fluctuations, while they are still happening, appear to be less dramatic in the last decade.

One of the project’s lead researchers, Professor Dan Nussey, said the shift could be linked to a warming climate.

“The increases and then declines over particular winters in sheep numbers we observe on St Kilda are striking, but not at all unusual in wild animal systems,” he said.

The Soay Sheep Project has been ongoing since the 1980s | Ian Stevenson

“Over the last 10 to 15 years, we haven’t see evidence of one of these more significant winter declines in the population.

“The population looks like it has stabilised at a slightly higher level than historically speaking. The degree of fluctuation seems to have dropped.

“It would seem this is likely to be linked in some way to climate change. We know that conditions are warming and becoming wetter on St Kilda, as they are in many places, and obviously more variable as well. There is some evidence that the growing season might be lengthening which could be playing a part.”

A recent paper by Professor Robin Pakeman, a senior scientist at the James Hutton Institute, showed evidence of rising plant productivity across the island Hirta, linking it to the growth of the sheep population. The effect was seen not only in vegetation favoured by the animals but also in less preferred or inaccessible areas, supporting the conclusion that overall food availability is increasing.

Graph showing the fluctuations in deaths that are still happening but have reduced over time | Soay Sheep Project

Prof Nussey added: “The research project has been running consistently for over 40 years now. It’s length and the detail of information we collect on individuals across their lifetimes is what gives us the possibility of potentially getting underneath what’s driving the changes we see on St Kilda and, more broadly, of understanding how the changing environment will impact wild animal populations.”

The team behind the Soay Sheep Project, while monitoring the sheep and studying the animals in their natural environment, have no role in the way the animals are managed.

The island and ongoing management is under the care of the National Trust for Scotland (NTS).

Earlier this month, a council meeting heard renewed concerns from some campaigners, including Western Isles councillor Gordon Murray, about the welfare of the animals, which, under Scottish Government policy, are deemed ‘wild’ and have a similar classification to deer or wild goats.

Councillor Murray pointed to an annual report on the Soay sheep confirming some 600 sheep die on the island each year.

The NTS confirmed it has an ongoing investigation into the welfare of the sheep. A spokesperson for the Trust said results of the study are due to be published by the end of the year. The Scottish Animal Welfare Commission (SAWC) is also conducting an independent welfare and ethical review the sheep.