Outdoors: Once prized for their pelts, pine martens are now treasured for their natural beauty

Near Insh in Strathspey is a delightful little birch wood that undulates its way down a slope towards the vast boggy expanses of the Insh Marshes.

It is always worth scanning the ground in such woods because the open margins hold interesting flora such as tormentil and eyebright. But regular examination of the leaf litter will also bring into sight strange-looking dark and twisted animal droppings, many of which have been deposited upon a rock or tree stump.

They are too small to be that of a fox and are in the wrong place and too numerous to belong to an otter. The perpetrators of these musky scented droppings are in fact pine martens, for a long time classed as one of our rarest mammals but which in recent decades have spread from remote Highland retreats to many other parts of Scotland.

The size of small cat, it is without doubt one of our most attractive mammals thanks to its bushy tail and rich dark-brown coat finished off with a creamy yellow bib. The naturalist Frances Pitt was so taken by the pine marten that she wrote: "Imagine it as remarkably graceful and nimble, with an expression of intelligent curiosity, and you will have some idea of a most beautiful being."

Until the 19th century pine martens were widespread in Scotland and many other parts of the UK, but relentless persecution by gamekeepers and high demand for their luxuriant soft pelts soon saw the population plummet. Records from one estate near Glen Feshie in the Cairngorms reveal that 246 pine martens were despatched between 1837 and 1840 alone.

Such enthusiasm among land-owners to rid their land of pine martens was probably in the most part misplaced, for rather than being an avid devourer of game their diet comprises principally of voles, mice, rabbits, small birds, insects, berries and fungi.

By the beginning of the 20th century the pine marten was only holding out in remote areas of the north-west Highlands. But since the Second World War there has been a remarkable turnaround in fortunes, with afforestation and reduced persecution helping to fuel a recovery in numbers, which began slowly but has really gathered pace over the last couple of decades.

Pine martens now even occur close to the urban fringes of Glasgow and Stirling, having colonised many forests in the Trossachs area including at Loch Ard and woodlands around Callander. It is now tolerably frequent in many areas north of the central belt, especially Perthshire, Argyll and Strathspey. There is also a small outlier population centred on Glentrool in Dumfries & Galloway, the result of the introduction of several animals in the early 1980s.

The pine marten is an excellent climber and will often make its breeding den in a tree hollow or in a bird or squirrels' nest. Scottish pine martens do not prey extensively upon red squirrels as is popularly supposed. Despite their arboreal agility, pine martens mainly hunt on the ground and the red squirrel is too nimble and fleet of foot in the trees for it to feature as a regular prey item.

However, in recent years there has been the suggestion that the growing pine marten population may play a role in helping halt the spread of the grey squirrel, which has displaced the red in many areas. The grey squirrel spends more time on the ground than the red, and is not so agile as its smaller cousin. This would certainly suggest that where the two animals occur together, the grey squirrel would feature as a prey item.

The evidence for pine martens playing a role in controlling grey squirrel numbers is largely anecdotal and it is a topic that merits detailed research. But it would indeed be a marvellous twist of fate if the pine marten proved to be the saviour of the red squirrel in Scotland.

This article was originally published in The Scotsman Magazine on Saturday 23 October 2010.