St Kilda's unusual meat-eating field mice

Meat appears to have increasingly become part of the diet of St Kilda's unusual field mice.

The mice are thought to have arrived on the remote archipelago with the Vikings or with the isle's first residents.

A lack of predators and a need to adapt to the cold is believed to have played a part in why the mice can grow to twice the size of mainland field mice.

Scientists have noted the mice are eating meat by either preying on birds or scavenging on dead ones.

On the mainland, field mice mainly feed on seeds from trees, but also insects, berries, nuts and fungi.

St Kilda's field mice inhabit the islands of Hirta and Dun.

They mostly eat snails, insects, moss and plant seeds, though some have previously been seen feeding on the carcasses of the island's Soay sheep.

The archipelago's huge seabird colonies could also be a source of sustenance for some of the mice on Hirta.

The National Trust for Scotland, which manages St Kilda as a Unesco World Heritage site, said there was also evidence from isotope analysis that they were eating marine protein, which would suggest seabirds or their eggs.

Ecologist Conor McKinney told BBC Alba's Mermaid Tales programme their larger size had allowed the St Kila mouse to take advantage of different foods.

Mr McKinney said: "One of the things we have found about the St Kilda mouse is these mice at the back of the island have started eating more meat.

"We don't know if it is predation or whether it is scavenging of dead birds, but that is one thing we have started seeing."

Mr McKinney said it remained unclear how mice first arrived on St Kilda.

But he added: "They have been here for hundreds if not thousands of years."

A second kind of mouse used to be found on the islands.

The St Kilda house mouse - also larger than its mainland cousins - died out soon after the isles' last residents left in an evacuation in 1930.