BBC Wildlife Magazine
Dens for pine martens
Scottish foresters are attempting to boost the mustelid’s population to stave off the spread of grey squirrels
Red squirrel numbers have been in rapid decline across Britain in recent decades because of competition with introduced grey squirrels and transmission of squirrelpox virus, which is deadly to reds but leaves greys unscathed.
Until now, the Highlands and northeast of Scotland have been red squirrel strongholds, with no grey squirrels across this huge area except for in Aberdeenshire, where they don’t yet carry the deadly virus. But grey squirrels spreading across the Highland line, and into Aberdeenshire, means that squirrelpox could also spread.
Now Forestry and Land Scotland (FLS) is hoping to protect northern reds by enlisting the help of a squirrel predator – the pine marten – which has reduced grey squirrel numbers in other places without significant impact on the more agile reds. Red squirrels have coexisted with pine martens in parts of northern Scotland for the past four decades among native trees and mixed plantations.
“We need to stop grey squirrels in their tracks,” says Gareth Ventress, environment forester at FLS.
Installing over 30 pine marten ‘den’ boxes along potential grey squirrel migration routes north is a key part of the FLS plan.
“We’re not introducing pine martens to these areas,” he says, “They’re already there.”
But foresters can improve pine marten breeding success by installing roofed wooden boxes in areas with few of the natural tree holes that martens prefer as denning sites. The boxes are erected a few metres off the ground and lined with wood shavings to keep martens – including youngsters – cosy.
The FLS team has placed artificial dens in several forest locations along two major corridors of grey squirrel advance – in the heart of the Highlands from Perthshire northwards, and up to and around Aberdeen along the east coast.
Boxes will be checked this May to see if they have been occupied. Pine martens circle like dogs when they lie down, says Gareth, which disturbs the wood shavings. They also tend to scat on the roof of the den boxes. So fieldcraft and woodwork will now be combining to help keep the greys at bay.