Anja Murray: Our rarest native mammal — the pine marten — is making a comeback

Being so agile and adaptable, pine martens were known here as ‘cat crainn’ — ‘tree cat’. Like cats, they are carnivores, adept at catching small woodland birds such as robins and wrens, and nimble enough to catch squirrels, mice, rats, shrews, voles, frogs, and lizards too

For thousands of years, pine martens have been common across Ireland, clambering among the canopy of woodlands that once blanketed the landscape. But by the 1970s, these woodland predators came near to extinction here. Now, the benefits of their recovery is ricocheting through Irish ecosystems and helping red squirrels to gain lost ground too.

Being so agile and adaptable, pine martens were known here as ‘cat crainn’ — ‘tree cat’. Like cats, they are carnivores, adept at catching small woodland birds such as robins and wrens, and nimble enough to catch squirrels, mice, rats, shrews, voles, frogs, and lizards too. They will happily snack on smaller creatures such as beetles, earthworms, woodlice, spiders, and snails. In late summer and autumn they top up their meaty diets with vitamin-rich tree fruits such as haws and rowan berries. The few times I’ve glimpsed a pine marten I’ve been struck by how beautiful they are, with a sleek covering of rich chestnut brown fur, big dark eyes, and cute rounded ears that are highlighted by a rim of paler fur.

Pine martens feeding on meat laced with strychnine is thought to be the factor that eventually brought them to the brink of extinction here

They have evolved to live in temperate deciduous woodlands — but being a woodland animal did pine martens no favours, as Ireland's woodlands were reduced over the centuries to only about 1% of our land area by the beginning of the 20th century. In addition to suffering severe habitat loss, pine martens endured centuries of persecution at the hands of humans. Their adaptive appetite means that they also eat carrion [dead animals]. With the surge of sheep farming in the last century came the practice of laying out carcasses loaded with strychnine — a deadly poison intended to kill foxes. Pine martens feeding on meat laced with strychnine is thought to be the factor that eventually brought them to the brink of extinction here.

By the late 1970s, pine martens had suffered an estimated 90% loss of their original population. Small, fragmented populations managed to cling on in suboptimal habitats in just a few parts of the country, such as rocky, shrub-covered slopes in western counties and especially, in the hazel woodlands of the Burren in County Clare. Despite recent recovery, they are still one of Ireland's rarest mammals.

Globally, there are 11 related species, all part of the family known as Martes and many are under threat from habitat loss and persecution. For example, the ‘fisher’, a small carnivore that lives in the Boreal forests of Canada and the northern United States, is in decline due to the ongoing clearance of these rich ecosystems. A whopping 12% of the fisher’s range has burnt in only the last six years — and large-scale, clear-cut felling continues there too. This global context makes the recovery of the European pine marten here a particularly positive and uplifting story.

European Pine Marten: globally, there are 11 related species, all part of the family known as Martes — and many are under threat from habitat loss and persecution

Another prey item on the long list of things that pine martens like to eat is squirrels, both reds and greys. But because pine martens and red squirrels have evolved together in a natural predator/prey relationship, red squirrels understand very well their place in this relationship and know to be wary when they smell a pine marten. Grey squirrels, on the other hand, were only introduced just over 100 years ago, and because grey squirrels haven’t co-evolved with pine martens, they aren’t as wary of the smell of this particular predator. This means that pine martens catch far more grey squirrels than reds, a dynamic which in turn helps keep the invasive greys in check.

In a classic ecological tale of ‘the enemy of my enemy is my friend’ the increase in range and density of native pine marten populations has, in turn, been linked to the reduction in invasive grey squirrels and the recovery of native red squirrels. I like to see it as a form of inadvertent restorative justice in the world of our native mammals.

Grey squirrels are classified as a pest due to the damage they cause to timber through bark stripping, as well as competing with, and spreading infection to, native red squirrels. The recovery of our pine marten populations is helping to repair the severed threads that bind our ecosystems together, indirectly helping to restore so much more than what we might expect. Nature is once again providing solutions to our mistakes, always working to weave those threads together again.

Nothing to see here, just our local pine marten breaking into the kitchen... pic.twitter.com/0W3NMP4Wyp

— Tom Spencer (@TPSpencer88) November 13, 2023

This recovery of pine martens is a result of legal protection, a ban on the use of the poison strychnine, and an increase in tree cover across the country. Now, pine martens are present again in every county on the island. As pine martens reclaim their position as a common mammal across Ireland, they are once again having to adapt to quite a different environment to the one they evolved to thrive in. Most of the forests that account for the rise in tree cover in Ireland are coniferous heterogenous plantations, with little diversity of species or suitable denning sites for pine martens. The lack of suitable breeding habitat has meant that pine martens, clever and adaptable as they are, have started to use attic spaces in people's houses to give birth and raise their kits.

Pine martens have many admirable qualities, though they are definitely not clean or quiet house guests! People who find that these furry carnivores have moved into their attic tend to be less than impressed, though many are being persuaded to tolerate the marten family until the young are weaned and the family unit leaves voluntarily. Once departed, the access point can be sealed to prevent the martens from returning the following spring.

Another option is to provide the pine martens alternative accommodation away from the house in the form of a ‘den box’. During 2023, the Vincent Wildlife Trust ran a workshop for National Parks and Wildlife staff on designing and erecting den boxes to re-home unwelcome house guests and allow them to rear their young in safety.

These gorgeous animals are a legally protected species, it is in all our interest to allow their continued recovery. Not only do red squirrels benefit, but so do the trees that might otherwise be stripped by greys — and the wider woodland habitats, and by consequence our climate, water quality, and overall health of Irish ecosystems also benefit.

Click here for more information on pine martens in Ireland