Pine martens were once common in the South West, but a loss of their woodland habitat and human persecution caused their extinction, conservationists said.
The animals can be found in Scotland and Ireland, with reintroductions in Cumbria, the Forest of Dean, Dartmoor and Exmoor.
“We have been utterly staggered to see one,” said Kottler.
“At this stage, we don’t yet know whether the animal is a transient visitor or resident to the area.
“We’ll be continuing monitoring in the coming weeks to better understand its presence, potentially even whether it could be part of a breeding pair.”
Kernow Conservation said pine martens’ “gradual recovery across the UK means moments like this could become more common, but seeing one here, now, is something truly special”.