Why our red squirrels are out on a limb

The wildlife film-maker Stephen Mills once filmed a red squirrel feeding happily in the crown of a spindly Killarney oak tree as it was being whipped about in a gale. He wrote of squirrels brandished by gusty winds like little mops in the tree tops - a good image to hold on to when your slates start rattling again.

As for cosiness, you could do worse than picture the squirrels' winter nest, or drey, a football-sized sphere of woven twigs jammed in a fork at least six metres up, safe from any flood and so well lined with leaves, moss, feathers and bark that it is waterproof and much warmer inside than out. Here, a squirrel can sway away the night, curled up in its tail. It does not hibernate, however, whatever the temptation on drenching autumn mornings, and is out foraging soon after day-break.

But how safe ecologically are our red squirrels? Decades of reports from Britain and Wales have chronicled the ousting of the red squirrel, by the introduction of the American grey squirrel, possibly to the point of extinction within the next 20 years. But while the spread of the grey in Ireland is certainly quite rapid and relentless, there does not seem to be the same inevitability that its advance will exclude the native species. A lot will depend on the kinds of trees we grow, and in what mixtures. Ironically, the current ecological agitation for a bigger share of broadleaved trees in national forestry policy - of oaks, in particular - could leave the red squirrels even further out on a limb.

While the reds are holding their own in coniferous forests, they seem unable to compete with greys in broadleaved or mixed woodlands. Some researchers have concluded that reds are unlikely to persist with greys in woods of more than 14 per cent of oak canopy. This makes it likely that the new and restored native woodlands now being planted under the Millennium Forests programme will be populated by the alien greys. Indeed, the much-criticised monocultural plantations of Sitka spruce could offer the native red its last refuge.

Current distribution maps of the two species in Ireland show the greys extending down the eastern half of the island, with blanks in Antrim, Donegal and round the south-east coast. The reds are still settled to the west of the Shannon, across most of Munster and south Leinster, and in patches of the Glens of Antrim. The two have big areas of overlap, however, in the southern midlands and the border counties. And in the centre of the island, extending eastwards from the site in Longford where eight American grey squirrels were released in 1911, the woods are largely empty of reds. The greys have been moving outwards at about three km per year, but in some parts have doubled that.

Ireland's native squirrels are thought to have died out in Tudor times, perhaps due to deforestation and overhunting for their skins, and today's population stems from reintroductions in the 19th century. Reds are naturally adapted to living scattered throughout the canopy of conifer forests, while the heavier, less agile greys prefer deciduous trees, where they live at a higher density and spend much more time on the ground.

The reasons why greys displace reds (or not, as the case may be) are subtle and still not fully understood. It is not a simple case of bullying, or of infectious disease (as once seemed to be the case in Britain). Latest research has been concentrating on the competitive use of foods.

Both species have a broad diet. Both, for example, chew on woodland mushrooms in autumn, and supplement their staple tree seeds with berries, tree-buds, flowers, barksap, and insects. The red squirrel concentrates on conifer seeds and the grey squirrel on acorns, beech mast and hazel nuts - but both will eat each other's food, especially when times are tough, and here the grey has a big advantage.

It can eat unripened acorns and hazelnuts, well able to neutralize the toxins they contain at this stage, and it hides them in caches from late summer onwards. The red can't digest acorns properly until they are ripe - but then it may find the seeds have gone when it needs them. The bigger grey squirrels, with more autumn fat, are also better able to survive hard winters and bad mast years, and can better digest poor-quality secondary foods.

There is still no hard evidence in Ireland of replacement of red squirrels by greys, but there are plenty of local observations of the sort science calls anecdotal. The ecological relationship between the two species is being studied by Donncha O Teangana in the north of Ireland and by Shane Reilly in the south; they have also carried out the latest distribution studies.

In hazel-ash woodlands in Co Fermanagh, grey and red squirrels seem to have coexisted for 40 years, and a radio-tracking study by O Teangana at Castle Archdale found red squirrels sharing a Norway spruce plantation with greys for 12 years without an apparent effect. Nonetheless, biologists accept that competitive exclusion is the long-term threat.

Even Sitka spruce is not a really hospitable habitat for reds, because it sheds its seeds in autumn, bringing the squirrels to the ground and within reach of predators. European conifers, such as Ireland's once-native Scots pines, hold on to their seeds in the cones through the winter and let the reds stay aloft to eat them.

There is now a Northern Ireland Squirrel Strategy, in which the Forest Service has earmarked areas for special conservation management. This will mean isolating chosen red squirrel conifer forests from any nearby deciduous woodland, planting a mix of conifers to guarantee a cone crop, and taking out the conifer species - such as Norway spruce - for which the grey squirrel also has an appetite.

Such red squirrel refuges have not yet been considered in the Republic. The most likely location would be in the west of Ireland, where the barrier of the Shannon continues to hold the greys back. There may be time to grow Scots pine as upland woods, or even to include them in the current restoration of native woodlands. Our reds deserve better refuges than ghettoes of Sitka spruce - and a chance of eating acorns at the proper time.