The feral mink: cold assassin or just misunderstood?

EYE ON NATURE:IT'S A CREATURE glimpsed at the corner of the eye, too small for cat or otter, too big and dark for a stoat, too skinny for a pine marten – a sinuous ripple into the shadows, leaving uncertainty behind. But then, it can be almost scarily fearless, approaching in broad daylight to sniff a fisherman's wader, or refusing to be chased from a half-eaten duck. Stoats can have the same kind of boldness, but fail to raise the bile engendered by Mustela vison, the feral American mink.

It still takes the blame for untoward rural atrocities. In August, an anguished Connemara sheep farmer, together with her neighbours, was sure that mink were killing her big lambs – 20 in one night. “They drink the blood,” was the story, “and bore the eyes and ears to get to the brain.” Well, mink do indeed go in for surplus killing, but, as territorial animals, they don’t hunt in adult packs. And at not much more than a kilogram, the mink does seem an unlikely choice of assassin, compared with rogue dogs and ravens. In 2001, Dr James Fairley, an authority on Ireland’s mammals, could find “no reliable account of mink attacking sheep or lambs”.

It’s half a century since mink started running wild in Ireland, escaping from fur farms or surreptitiously released when businesses failed.

They spread slowly south and west to rivers and lakes across the island (here at Thallabawn, the first was spotted on the shore 10 years ago, with hooded crows in raucous pursuit). They are now reckoned “highly prevalent” in the east of the island, but still with plenty of room for expansion in the west. A new estimate of the potential population, based on available watery habitats, is between 25,000 and 33,500 animals.

Back in 1991, when Dr Chris Smal made a milestone report on the species to the Wildlife Service, he was concerned to avoid “what might be futile and unnecessary attempts to reduce mink numbers”. Indeed, he added, “the mink may not deserve the reputation it has gained.” His work left hope that, after initial explosive assaults on native wildlife at the leading edge of colonisation, things would slowly settle down, as territories spaced out the mink and their predation was absorbed into the natural death-rate of birds, animals and fish.

Since then, the animal’s capacity for reducing or disturbing vulnerable species in particular habitats has become all too clear: the mink’s permanent eviction of an important colony of nesting sandwich terns from a coastal lagoon to the north of me is just one example. Control of alien species is now at the forefront of conserving global biodiversity, and the American mink is reckoned one of the world’s worst 100 invaders. In Scotland’s Hebridean islands, where mink were decimating nesting terns and gulls (a single mink destroyed a whole tern colony), some 4,500 traps were deployed across more than 1,000sq km. In England, seasonal trapping is used on the rivers that feed the Thames to prevent the minks’ local extinction of water voles.

Options for mink control in Ireland now figure in a new report commissioned by the National Parks and Wildlife Service. (Details of the methods, ranging over rafts, remote cameras, traps, scent glands, air rifles and dogs, may be found in the Irish Wildlife Manual No 40 at www.npws.ie). Its authors are Sugoto Roy (who managed the Hebridean mink project) and Neil Reid and Robbie McDonald of Queen’s University’s Quercus research centre. A trio of biologists from Queen’s University Belfast, and the UK readily acknowledge the vulnerability of many Irish bird species, from coastal terns and seabirds, to corncrakes, barnacle geese and whooper swans, and even the chicks of upland hen harriers. In rivers and lakes, too, mink could threaten salmon, lampreys and crayfish – all species listed in the EU’s Habitats Directive.

The need to protect special conservation areas – SACs, SPAs, NHAs – has prompted the new review. The NPWS has already started small-scale control of mink and other ground predators, mainly to protect terns and corncrakes, at 11 sites across the island, from western lakes to the Shannon Callows to the Wexford Wildfowl Reserve. But since mink can swim up to 14km, the review now voices concern even for storm petrels nesting on offshore islands, such as Mayo’s Inishglora, Inishkeeragh and the Stags of Broadhaven.

Analysing the experience of the Scottish and English trapping programmes, and those elsewhere in Europe and New Zealand, the team argues against trying to eradicate mink, which might “in an ideal world, with unlimited resources” be the optimal strategy. Reducing mink by three-quarters across 800sq km of river catchment over five years, for example, could cost more than €900,000 (and bounty schemes invite fraud and don’t work).

The realistic immediate strategy, concludes the team, is to focus intensive year-round control on areas where mink would do the most damage to “globally important populations of vulnerable species”.

Eye on Nature

On a recent visit to Skellig Michael I saw a Lapland longspur. It was hardly visible when it was on the grass.

Geraldine Lynch Burke, Leeson Park, D4

The Lapland longspur bunting is a scarce but regular visitor to west-coast islands and headlands on passage from the Arctic in autumn.

Working on the till in front of a large window in Books Upstairs, College Green, I had an unusual visitor – a grey squirrel. It headed for Éanna Ní Lamhna’s Wild Dublin on a shelf nearby, then scampered upstairs to the mezzanine and then found its way out.

Róisín Sheerin, College Green, D2

Be under no illusion, earwigs can give you a good nip. Their pincers, especially the male’s, can go into your finger like needles. I got nicked a few times when disposing of them eating my dahlias.

Padraig McGinn, Carrick-on-Shannon

I watched the migration of swallows with mixed emotions. The procession lasted for about an hour. I thought they would leave when the wind was in their backs, but what little wind there was came from the southwest. I wonder do they know more about impending weather than we do.

Ivor Kenny, Avoca, Co Wicklow.

Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo. E-mail: viney@anu.ie. Include a postal address.