Looking for a snuggle of wrens in a swallow's nest

EYE ON NATURE:THE SNOW took its time to reach the coast of Co Mayo, cloaking the mountains but leaving the hillsides green. But it was still cold enough to calm the whirl of birds at the feeders long before dusk, and send the finches, sparrows and tits early to their roosts in holes and thickets.

A reader’s photograph, e-mailed from Co Antrim, sent me out after dark on the chance of finding a snuggle of wrens in a swallow’s nest. Lesley Wishart took the picture in the porch of her home in Portballintrae, where wrens have been roosting on wintry nights for years.

The colder it is, she says, the more push into the nest. Once they settle, little heads pressed together in the dark and breathing warmer air, no one is allowed to use the front door.

So encouraged, I made the rounds of the swallows’ nests in the woodshed. The flashlamp showed me only the vacant brackets of mud high under the roof; even the tits’ nest-box was vacant. But this habit of wrens is well-documented, not least by the Belfast parson/naturalist the Rev Edward Armstrong, who wrote a whole book about the species. Wrens usually roost alone, he observed, but in bitter weather a male may call several wrens together to search for a snug roost or to share one he already knows about.

Fifty in one nest-box seems to be the current record.

Long-tailed tits are another species given to such intimacy, flying by day in little groups and clumping in a ball at night, their tails sticking out, on a branch at the heart of a hawthorn bush. Like wrens, they often use the same place for weeks, but are quite unlike other tits in roosting in this way. Follow a coal tit at dusk and it will vanish among green tufts of conifer needles; great tits and blue tits, too, seek individual shelter in crevices and tree holes, tucking beaks and legs into their feathers. Where blue tits have paired early in a winter flock, the male sees his mate to bed, then goes to roost nearby.

Cold snaps, if brief enough, do little harm to wildlife. Snow itself rarely kills, but it acts like an insulating blanket, keeping the ground at around freezing point while the outside air may be several degrees below. But a bird’s size can be key to survival. For tits, wrens, goldcrests, a large body surface in relation to size means a high metabolic rate, needing constant food to stay warm and active. A really harsh, protracted winter, with glazing frosts day after day, can reduce such little birds to one tenth of their populations or even wipe them out locally, as happened memorably in 1962.

Birds in general have the highest body heat of any animals, and fluffed-out feathers give good insulation, even in quite severe conditions.

Even on a frozen lake, a swan maintains 105 degrees Fahrenheit ­– a fevered temperature in a human – and the venous blood returning from its icy feet is passed through a coil of warm arterial blood before it reaches the body core. Birds resting one leg usually have the other tucked up into their feathers, warming each in turn.

But iron-hard weather can force birds out of their normal behaviour: lapwings joining thrushes to forage in farmyards; rooks killing and eating other birds; snipe and curlew trying to pierce frozen mud in ditches beside busy roads.

Even migration may not let birds move far enough, fast enough, to outpace weight-loss in the grip of cold. In the big freeze of early 1985, there were huge movements of Scandinavian redwings to Ireland. On one day that February, a man living at Newcastle on the coast of Co Wicklow found the sky suddenly darkening above him as a great flock of the little thrushes flew in from the sea.

They took several minutes to pass and “flopped down into the fields” – 10,000 birds was his guess. Once rested and fed, many of them carried on west, only to expire, finally, at the very edge of Europe. I found them dead by the dozen on the last grassy headlands at the shore. (A roosting redwing was one surprise of my night-prowl after wrens, blinking into my flashlamp from the evergreen depths of an escallonia bush.)

As I write, the “cold snap” has a few days – at least – still to run, and its consequences for the birds have yet to be assessed. It is at times like this that garden feeders have a value far beyond human entertainment, at least for seed-eating birds.

The glorious goldfinches are the latest species to discover human hospitality, but who knows what has been turning up lately at bird-tables and nut-holders? BirdWatch Ireland would welcome the details: you can download its Garden Bird Survey form at www.birdwatchireland.ie or even give the records online.

Ireland’s Ocean: A Natural History by Michael Viney and Ethna Viney has now been published by The Collins Press, Cork.

On a recent walk along the tow path beside the River Suir in Co Tipperary, I came across an otter walking along. He stared me and the dog down and would not move. “My patch,” he seemed to say. “Move along.”

Nick Ahearne, Clonmel, Co Tipperary.

The grey squirrel takes mouthfuls of moss out of my lawn. He then scuttles off up the pine tree. What is he doing? Joseph Clarke, Greenfield Park, Dublin 4.

It was probably a female squirrel using moss to line a nest or dray for her approaching litter.

Recently, I was amazed to see a barn owl flying over Dublin’s rush-hour traffic on the N3 between the Ashtown and Castleknock roundabout.

It seemed to be flying towards the Phoenix Park. I have never seen a barn owl in the depths of winter and certainly not in such an urban area.

Helen Butler, Athboy, Co Meath.

On Christmas Eve, during a mild spell, I saw my industrious bees carrying in loads of yellow pollen from blossoms of nearby gorse. What is the payback to the gorse for blossoming in mid-winter. Can they set seed at this time of year?

P Finnegan, Cliffoney, Co Sligo.

Most seeds will not germinate below 4.5 degrees C.

Send observations to Thallabawn, Carrowniskey PO, Westport, Co Mayo orviney@anu.ie. Include a postal address