Halting the march of the grey squirrel

Another Life: When foresters talk of grey squirrels as "tree rats", biology supports their bile: squirrels are rodents with fluffy tails (there are scaly-tailed squirrels, too, but not in European woods). The red squirrel is just as much a rodent, but has a more glamorous pelt, native Irish credentials, and a fonder public image. Above all, it lacks the grey's compulsion to strip bark from the stems and branches of young broadleaf trees.

It's a decade or more since Coford, the National Council for Forest Research and Development, listed grey squirrels as the top problem in protecting commercial stands of broadleaves.

"A severe attack," it said in 1994, "can reduce a promising crop to firewood potential within a short time." The greys are now spreading out of control, and their destructive habits have brought increasingly angry reaction from private foresters. Coford now calls them "a serious threat to existing and future broadleaf planting".

Its new response is a three-year project funded by the Forest Service and focused on 11 woodlands in the Meath, Westmeath and Kildare. These all have grey squirrels and some have reds as well.

Coford is looking for a project officer to estimate and monitor numbers, assess the level of tree damage, and help draw up protection strategies for a national programme of control.

While greys are to be "managed" with dire prejudice, red squirrels are to be cherished and conserved.

From its innocent "big house" introduction in Co Longford in 1911, the American grey squirrel now extends down the eastern half of Ireland. The Shannon, long a barrier, seems to have been breached: squirrels can dog-paddle, if not from choice, and there have been reports of crossings into parts of Co Galway. Elsewhere, the greys' outward progress has been logged at three kilometres a year, and sometimes a lot more.

Red squirrels are still flourishing to the west of the Shannon, across most of Munster and south Leinster, and in patches of the Glens of Antrim, but there are big areas of overlap in the southern midlands and the Border counties.

In the centre of the island, extending eastwards from Longford, the woods are now largely empty of reds. Most of Britain, too, has lost its red squirrels in the spreading tide of greys.

The greys are more robust and omnivorous animals, with a stronger digestion (for the tannin in acorns, for example), and are more used to foraging on the ground. They get fatter in winter, while the reds must stay light and nimble to harvest the highest pine-cone seeds.

Outcompeted for food in bad seed years, the reds progressively give way to greys, at least in the broadleaf woodlands the greys prefer. They are also accused of spreading the parapox virus, to which reds are susceptible but greys are not.

Bark-stripping (to get at sweet, sappy tissue beneath) may be a "learned" behaviour prompted by overcrowding: greys at home in America do far less damage. As Coford studies have already shown, young sycamore and beech are the trees most at risk, with 40 per cent of them damaged from six years old onwards, and as many as 16 per cent of sycamores completely girdled, or ring-barked.

The damage is done between mid-March and June, when young squirrels are forced out of their birthplace to find woodland of their own. How are their numbers best controlled?

Shooting has never worked: the greys are too hard to see. Warfarin, the rat poison, or snap-traps, risk killing too many other things - not least red squirrels. Birth-control baits that work exclusively on greys have yet to be devised.

Coford's best advice so far is cage traps - one per hectare - baited with maize kernels and made with weighted doors to avoid catching anything smaller. Red squirrels can be released and greys humanely killed.

In a long-term strategy, the Northern Ireland Forest Service is trying to create secure strongholds for the reds. Blocks of conifers have been isolated from broadleaf woods and planted with a mix of species to guarantee a good cone crop. But even these areas have been infiltrated by greys, who can have their own taste for conifer seeds from species such as Norway spruce.

The grey squirrel's toll on timber obviously matters most to commercial foresters: control is far less urgent in mixed native broadleaf woodlands and "amenity" planting, where calloused, crooked (or even topless, wind-snapped) trees are no disaster.

But the growing threat to our native red squirrel is not confined to the boundaries of commercial plantations, and its ultimate survival will also depend on refuges planned for in national planting policy.

Details from Dr Michael Carey (e-mail: careyml@eircom.net)