Otters numbers had been in decline

They will study more than 1,000 sites over the next two years to see whether measures to raise otter numbers are succeeding.

For years in the sixties and seventies, otters were under threat across Europe.

Numbers crashed as the mammals fell victim to industrial waste and chemicals polluting rivers.

Even in Scotland, once a stronghold for otters, they were in retreat.

But attitudes towards this protected species have changed and experts from Scottish Natural Heritage believe otters may be moving back into areas they had given up - especially in the south of Scotland.

Otter tunnels and underpasses have been included in new sections of road to try to cut down the numbers killed by traffic.

Cleaner rivers are helping too.