The tiny alien that calls our house its home

ANOTHER LIFE:What do you do with a shrew in the loo? This lunatic, unquenchable jingle was born of the latest addition to the biodiversity of what was once our cottage porch. Veteran readers will already be familiar with my meditations on its wildlife – woodlice, spiders, the dearg a dhaoil in the shower, and so on – so that the shift up the food-chain should come as no surprise.

The pygmy shrew is an arch-insectivore (like the hedgehog) and nothing to do with the mouse family, so that its rapid skittering around my bedroom slippers impelled only the lifting of feet lest some entomological morsel escape that quivering little snout and grinding, ruby-tipped teeth. Two hours without a meal and a shrew is in a bad way. “There is something indescribably sad, almost poignant, about a dead shrew,” wrote Belfast zoologist James Fairley once, “ flat on its back with its little legs in the air. As animal corpses go, only that of an elephant is more pathetic.”

As the smallest mammal we have, Sorex minutus actually shrinks further in winter – often to less than 3 grammes, around the weight of a 2c piece – and the negligible skeleton inside that little ball of dark, velvety fur permits an easy wriggle into the warmth of many rural houses. Ours is perhaps more permeable than most, so what one actually does about a shrew in the loo is let it come and go (meanwhile alerting one’s spouse; not that mine is much given to shrieks).

A winter shrew is one born last summer, its parents having died in the autumn, and it will be dead, in the same way, before next summer’s abundant young have grown their winter fur. Such dramatic turnover balances the population sprinkled widely and quite evenly through the Irish countryside.

This miniature mammal has, however, punched well above its weight in the scientific unravelling of Ireland’s post-glacial colonisation by furry wildlife. The island has mysteriously lacked the larger common shrew that, in Britain and most of Europe, overlaps with and often greatly outnumbers it. In the long to-and-fro of theorising about temporary, low-lying, soggy land bridges to Ireland after the ice melted, much was once made of the common shrew’s need to burrow after earthworms as a major prey, whereas pygmy shrews could survive on soaking-wet moorland, partly by leaping after midges (James Fairley once trapped a shrew on the summit of Carrauntoohil).

Genetic research, however, now suggests that, like most of our mammals, the pygmy shrew arrived along with people. DNA analysis has found the Irish shrews sharing a lineage with those of Andorra, that tiny mountain enclave above Spain. A limited range of genetic variation also argues for “an extreme founding event”, as one paper puts it – perhaps a single, accidental introduction of a family of shrews in a boat from Iberia several thousand years ago (or just conceivably, I suppose, on a wayward, drifting raft of vegetation).

Ireland’s steady absorption of “alien” mammals was highlighted in 2008 with the trapping of another European shrew – Crocidura russula, the greater white-toothed shrew – at four places in Tipperary. This followed discovery of its skeletal remains in barn owl and kestrel pellets collected in different parts of Tipperary and Limerick by ornithologist John Lusby.

This larger shrew, thought to have arrived en famille in the root ball of a big plant imported for an Irish garden centre, commonly enters houses and outbuildings in Europe and often makes a den in the warmer depths of compost heaps. With its larger size and four or five litters a year – twice the reproductive rate of the pygmy shrew – it seems very likely, in time, and with climate change, to usurp the pygmy’s present spread of territories.

Co Limerick, as it happens, was also the first bridgehead of another little widespread furry alien, the bank vole, that arrived in the 1920s with German earth-moving machinery brought in through Foynes to build the Ardnacrusha dam. In the absence of Britain’s field voles, it has further enriched the food supply of the Irish stoat – with the Irish hare, the only true mammalian survivor of the Ice Age on or around this island.

Dr Paddy Sleeman, UCC zoologist and an authority on the stoat, has long been intrigued by the gap in post-glacial prey available to the animal (hares generally run too fast to catch) and has come to the view the stoat may originally have been a coastal predator. In the current issue of the Irish Naturalists’ Journal, Mayo conservation ranger Eoin McGreal reports watching a stoat carrying a fish among shallow intertidal pools on Clew Bay, Co Mayo. This chimes with observations in “Eye On Nature”, in the late 1980s, of stoats catching fish among pools on the shores of Co Sligo and the Burren. It could thus be an adaptation peculiar to the animal’s evolution in Ireland.

Eye on nature

Three red squirrels have been coming to my nut-feeders more or less daily for the past two years. The ones not in possession of the feeder make noisy branch-shaking sallies to try to remove the incumbent. Recently one squirrel has been eating sunflower hearts, intended for the birds.

Tom Wilmot, Ballyshannon, Co Donegal

During the hard weather I had three snipe feeding in my garden. Later I saw a field where I counted 30. And driving home recently on the Waterford motorway, a flock of birds with long beaks, which could have been curlews, wheeled over me. There is quite marshy land beside the road there.

Rosemary Ryan, Tuitestown, Co Kilkenny

I spent 30 minutes watching two wheeling kestrels attempting to hit each other in mid-air while screeching at each other.

Paul Keogh, Fenit, Co Kerry

In the late afternoon, as is usual around this time every year, four different flocks of starlings flew overhead. They were tens, perhaps even hundreds of thousands strong and seemed to cover half the sky.

Justin Doyle, Virginia, Co Cavan.

Your starlings were amalgamating several flocks and gathering at a roost large enough to accommodate them. They were preparing to return to continental Europe from whence they came to winter here.

• Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo, or viney@anu.ie.
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