Steady As A Bomber

Impressionist scenes in the garden these mornings, new contre-jour RO]planes of colour and light. The young oaks fiercely green and black, flinging violet shadows on the grass; glittery spires of poplars in The Hollow, each leaf a separate flake of silver; hawthorn hedge thickly impastoed with white blossom; and beyond, the bright blue mountain in a flat wash of haze.

To this makeshift Monet, the cuckoo arrived like a sound effect, the air so still that the bird mimicked itself in the echo from the lake. It appeared, steady as a bomber, the pitch and interval of its idiot, two-tone call totally undeflected by the little birds fluttering in its slipstream. It settled on the ESB wire which, stretched invisibly across our view of the shore, has sometimes, by an optical illusion, populated the strand with giant rooks or Martian armies of starlings.

The cuckoo sat upright like a large, grey monk, attended at either side by a pair of meadow pipits: an oddly medieval tableau against the distant, creamy shimmer of sand. The bird took their little dashes and harassments with apparently stoical calm but then, after a retaliatory snap or two that showed the orange lining to its mouth, launched itself onwards across the hillside.

The automatism of the cuckoo's lifestyle has always somewhat repelled me: not just what it does in planting its egg in some other bird's nest, but its brazen display of programming and instinct - the raw workings of a set of selfish genes. Among birds it is peculiarly a robot, if one equipped with a sometimes baffling code of DNA.

Imagine, for example, what drives the cuckoo chick, freshly hatched, to empty the nest of all the competition. It apparently responds to any pressure that it feels on a specially sensitive, hollow patch on its back. "Attacked by epileptic power" (as one graphic description puts it) it gets underneath an egg, or fellow-nestling, slowly backs up the side of the nest with the object balanced between its wing-stubs, and hitches it over the edge. Then it collapses, exhausted, until it touches something else that feels as if it needs throwing out.

The cuckoo's ability to lay an egg that mimics, often quite closely, the eggs of the host-bird still presents what Edward O. Wilson calls "a first-class scientific mystery". Cuckoos have been recorded parasitising more than 125 species of bird throughout Europe and Asia, but each female cuckoo is thought to specialise in just one host - usually the same species that reared her. From one region and habitat to another, cuckoos become divided into a number of "races" which tend to focus on particular hostbirds. Thus there are pipit-cuckoos, dunnock-cuckoos, wagtail cuckoos, reed-warbler-cuckoos, and so on. But a male cuckoo often mates with females of more than one "race", and how the genes keep the specific egg-mimicry going within the female line remains baffling.

In Britain, the host-birds have long been identified with particular habitats - meadow-pipits in moorland and heathland, dunnocks and robins in woodland and farmland, reed warblers in marshland and so on. But in Ireland there has been a consensus among naturalists that the meadow-pipit is the cuckoo's chief foster-parent. After all, as Eamon de Buitlear pointed out in his book, Ireland's Wild Countryside, an Irish name for the pipit is banaltra na cuaiche, the cuckoo's nurse.

But mere consensus, backed up by folklore, is scarcely scientific. A couple of issues ago, Irish Birds, the research journal of BirdWatch Ireland, published a paper in which an American zoologist, Spencer G. Sealy, teamed up with John Halloran of UCC and Patrick Smiddy, the Cork naturalist, to test the supposition more closely. After all, just because pipits most often lead the mobbing of cuckoos, or are most often seen feeding their ravenous young, doesn't actually prove they are the cuckoo's chief victims. A check of 150 years of Irish natural history literature, an examination of egg collections in museums, and correspondence with field workers, confirmed 11 different species (including skylark, blackbird and linnet) as hosts to the cuckoo in Ireland.

But the meadow pipit came out way ahead, with more than 40 confirmed records of parasitism, and as the only species actually on record as rearing a cuckoo. In the museum egg collections, almost all the cuckoo eggs from meadow-pipit clutches were good-to-perfect imitations of the pipit's brown-speckled eggs, and only slightly larger than the real thing.

As farming leaves the meadow pipit with less and less rough grassland for nesting, the species has been declining in the south and east of Ireland - just the areas in which the cuckoo, too, has been growing scarcer. It may be, suggested the authors of the cuckoo-host paper, that the bird will switch its attentions to a new victim - perhaps the reed warbler, now colonising the south and east from Britain, where it is already among the cuckoo's favourite foster-parents.

Cuckoos don't count for much among the birds of Lough Corrib, but a good many other interesting ones do get proper mention in Corrib Country, a rambler's folding, guide and map just published by Tir Eolas at £5.95. The text is by the Galway botanist Cilian Roden, who has already contributed so well to books on the Burren and Aran, and there are many evocative drawings by Anne Korff.

A lake as big and diverse as Corrib, glimpsed from little piers and distant hilltops, is hard to grasp as any sort of whole. This guide is an excellent introduction to the natural history, and knowledgeable about the fascinating ruins tucked away on islands and leafy promontories.

It also, even in a limited compass, gives a feeling for the Corrib's vulnerability. Bang next door to one of Ireland's most rapidly-expanding cities, it holds floral limestone landscapes quite as fragile and precious as the Burren's, and an aquatic ecosystem alarmingly at the mercy of pollution. Taken with the work of the late Tony Whilde, this guide becomes a text for a badly-needed Corrib Heritage Trust, in which anglers, farmers, bird-watchers and B&Bs can all find common cause.