Diving dippers

THE mountain river crosses the boreen most of the time, on a final, deep swerve to its channel in the strand. In winter it can tug at one's wellingtons quite hard, so that, out for a walk together, Ethna and I hold hands to keep a footing on the rolling stones, and Meg the dog arrives at the far side somewhat down stream of where, she meant to land.

Some years ago, in a big flood, the river jumped a bend and tore, straight through a good grassy field leaving the ford and the little waterfall above it quite dry. But now, much to our pleasure, it has returned its old bed, babbling round our boots and washing the wheels of the tractors on their way to collect shell sand.

Crossing there the other day, we disturbed a small, dark bird at the waterfall. It flew upstream, in a low zig zag, and we knew it for a dipper, the little, white bibbed bird that can walk underwater. Seven years ago, says my nature diary, on February 14th, we saw one in the same place, so that would have been before the river moved away.

There was a time when all the bird books agreed that dippers were birds of fast flowing upland streams. It took the private passion of a Coleraine bank official to find that Irish dippers, at least show plenty of exceptions to the rule.

Kenneth Perry did his teenage birdwatching in the Republic, where he was born, and rather than "twitching" after rare vagrants decided to make a special study of one of our own, endemic birds. The Irish dipper is a distinct race within its species, with the most sombre plumage of all the dippers in western Europe. Perhaps, as an island bird, it had developed other differences.

Perry started his study on the River Shanganagh, in the hills overlooking Dublin and Dun Laoghaire, and he continues it today, after more than 30 years, on the rivers that flow into Lough Foyle and Lough Swilly. In 1986 he published, privately in Belfast, his book The Irish Dipper, and his later work appears in Irish Birds, the research journal published by BirdWatch Ireland.

To watch dippers feeding, courting and nesting, he has set up his hide and camera mostly below bridges, where dippers commonly nest beneath the arch, in a crevice or on a protruding stone. These are also, unfortunately, favourite dumping grounds for old bedsteads and motor cars, dead sheep and cattle which can rather blight the idyll of such observation.

It was in north Mayo that Perry found "the wee water hen", as many farmers know it, nesting in river banks, well away from bridges. And in Co Derry and Co Donegal he found it just isn't true, as books usually suggest, that most dipper nests are above the 1,000 foot contour. Most of his study nests ranged from 30 feet above sea level up to 400 feet.

Some have been in weirs and waterfalls - actually inside the curtain of water or spray - where the large, domed nest of mosses, picked from rocks and from under the water, is quite invisible. It took Perry years to find the first of these, under a weir in the middle of a village in Co Down. The mosses are often dripping with water, but within is a dry bowl woven from grasses and lined with leaves.

Dippers are very loyal to their nests from year to year, and February is the month when they start visiting them and doing them up. So of course we are wondering what that dipper was up to, hanging around a weir sized waterfall not far above sea level. Yet the river here is positively bleak, and furnished with drifts of rolling stones that, indeed, gather no moss.

It is, undoubtedly, just part of a territory which runs through a glen of willow scrub to an ivy hung bridge: classic dipper habitat at this low level. So now I shall watch more closely, and listen for a song which is well worth hearing. It reminds Kenneth Perry "of both wren and dunnock but with the quality, volume and sheer delight of a nightingale". The dipper sings in most months, but saves a special, throaty warble for its courtship.

The bird was obviously a favourite of Richard Ussher, writing in Birds of Ireland a century ago: "Its mode of alighting on, or dropping into, flowing water, disappearing, remaining submerged, reappearing gradually, leaping out and floundering in it, and the use of its wings under water are characteristic of this strange creature."

Once, coming upon a nest beside a mountain waterfall, he saw the young fledglings throw themselves into the pool below, "rowing themselves away from me with their wings under water and only creeping out when they got behind the waterfall".

For much of the time, in a stream with shallows, the dipper does no more than walk about, dipping its head under water to feed. But it does submerge in deeper water, "flying" against the current to reach the bottom and staying there for up to 30 seconds. To get a good view of this happening, says Kenneth Perry, "must equal the wonder of the stoop of a peregrine falcon or the food pass of a hen harrier".

At this time of year, the dipper is turning over stones underwater and picking off the armoured cases of caddis fly larvae, which it smashes on a rock, like a thrush with snails. By nesting early - sometimes in February - it is also able to exploit the spring abundance of food such as midge larvae and May fly nymphs.

The slightly warmer water of Irish hill streams (compared with those in Britain) probably leads to an earlier breeding season, with fewer second clutches of eggs. There seem to be more second broods on the lower reaches of the rivers where prey can be larger and easier to catch.

Like Ireland's otters, the dippers are a measure of clean water in our minor streams, and the upward trend in breeding dippers on Kenneth Perry's north western rivers (in fact, a doubling over the 20 years to 1992) is good news.