ANOTHER LIFE: Assassination by marksman's rifle of all of Britain's ruddy ducks (a description, not an expletive) must rank with the more surreal endeavours in nature conservation. Introduced from America 60 years ago into UK waterfowl collections, the ruddy duck not only flourished but has been emigrating to Spain, where it interbreeds with the globally threatened white-headed duck, writes Michael Viney.
To improve the genetic chances of the Spanish population - the last 1,000 of the species in western Europe - the ruddy ducks of the UK (including, presumably, those swimming around Oxford Island in Lough Neagh) must be reduced to 175 birds within 10 years.
Also this spring, all the hedgehogs of the Uists, in Scotland's Outer Hebrides, will be live-trapped, anaesthetised and killed by lethal injection. Introduced to the islands long ago, they are now decimating breeding colonies of wading birds by eating their eggs. Feral American mink on the Uists are also to be eradicated, at a cost of some €2 million.
Such high-profile (and high-cost) ventures accompany a whole new programme in the UK to combat alien species that threaten to take over from native plants and animals. Ireland inherited many of Britain's long-established "mistakes" in plant introductions, such as the rhododendron, Japanese knotweed and giant hogweed, and made its own unwitting blunders with American grey squirrels and mink (both of which are now past any national eradication).
In a report on alien species to the UK's Department of the Environment, Plantlife International put the threat to native biodiversity from invasive plants as second only to habitat destruction and decline. And fear of new insect pests which could survive in a changing climate has prompted the spraying of packing cases and sterilisation of soil around the roots of imported plants. Already, in Ireland, New Zealand flatworms imported in potted plants are spreading as a predatory menace to our earthworms.
Our terrestrial habitats have adapted to a long procession of species that have colonised the island naturally or been introduced since the Ice Age. But among the anxieties we now share with Britain is the sudden arrival of freshwater and marine species that could devastate aquatic ecosystems.
The zebra mussel from Eastern Europe, now smothering native species in the Shannon waterways, is just the best publicised of such accidental immigrants.
Sargassum muticum, is a finely-branched brown seaweed, buoyed up with pea-like bladders, that grows in Japanese waters as a small, unassuming seaweed no more than a metre long. Brought to European waters, however, it has become highly invasive, able to grow by 7 centimetres a day. Its floating mats, up to 12 metres long, shut off the light from native plants and animals on the seabed. It reproduces sexually, releasing thousands of "germlings" to settle and grow, and by floating fronds and fragments that continue to spread germlings as they drift.
The weed was first discovered in Ireland in 1995 at Strangford Lough, a centre for oyster farming, then in Cashel Bay, Connemara, and more recently in counties Kerry, Sligo, Wexford and Cork (to report a sighting, contact Dr Dagmar Stengel at the Martin Ryan Institute in NUI Galway: E-mail dagmar.stengel@seaweed.ie or phone 091-750387).
Aliens such as Sargassum, along with new, aquatic parasites and diseases, have arrived in transplanted oyster seed or other aquaculture imports and in the ballast water of ships. Exotic marine animals are spreading to Ireland from Continental and British coasts. In a recent review of species, Dr Dan Minchin warned of the "inevitable" spread to Ireland from the French Channel coast of the Japanese shore crab, Hemigrapsus penicillatus, a bully of a species outside its own ecosystem that can overwhelm the native green crab of our rock pools.
Meanwhile, this astonishing spring has produced an alien to sharpen the eye of everyone who takes pleasure in butterflies.
On March 27th Frank Smyth, an experienced recorder, was checking a small, mixed wood around Sutton House, near Howth in Co Dublin, and saw a bright orange butterfly, like a small tortoiseshell, basking on a bramble. A closer look found the scalloped wings of the comma butterfly - a ragged shape that helps it disappear when hibernating among dead leaves.
The comma is common enough in most of Europe, and in Britain has made a striking comeback in England and Wales. The first modern Irish record, in August 2000, was of two or three flying around the dunes at the Raven Reserve in Co Wexford. Subsequent Augusts have brought further records as far north as Donegal.
This species has a flexible life-cycle that allows it to add an extra brood when the weather feels good. If last month's butterfly was one that had overwintered locally, climate change may have brought us yet another resident from the south. For further news of butterflies, try the new website www.butterflyireland.com, run by the Dublin Naturalists' Field Club.