Science: Squirrel Nutkin v the squatters: Malcolm Smith looks at ways to increase numbers of the indigenous red creatures and cut those of the grey interloper

When, in 1920, Archibald Thorburn illustrated and wrote his classic book, British Mammals, he had no hesitation in labelling one of Britain's better-known mammals as the 'Common Squirrel'. The creature, described by Thorburn as 'indigenous and common in most wooded districts . . . in England, Wales and Scotland', is that enchanting star of The Tale of Squirrel Nutkin, the now all too uncommon red squirrel.

A human generation on, our native squirrel has been very largely replaced across almost all of England and Wales by that import from eastern North America, the grey squirrel. Famous for its TV high-wire acts and for befriending anyone with spare peanuts in many a town and city park, the grey version is the only squirrel most British children have seen.

As the seemingly inexorable spread of the grey squirrel - described as vermin by foresters, who deplore its attacks on young trees - continues northwards through northern England and into Scotland, many mammal experts fear that our red squirrel will not survive.

If it does, the chances are that it will do so only in a few isolated conifer plantations. And then only if land management and habitat manipulation - to encourage reds and discourage greys - is maintained. Ironically, much of this manipulation is quite contrary to what conservationists and foresters would normally do to improve plantation forestry and woodland habitats for wildlife.

John Gurnell, of London's Queen Mary and Westfield College, and Harry Pepper, of the Forestry Authority - both leading experts on red squirrels - have recently published a detailed assessment of the likelihood of such efforts succeeding. They conclude that it all depends on how much conservation effort is put in for this one species.

The trick is to favour red squirrels while discouraging greys. The problem is that while it is clear that greys have replaced reds in England and Wales, experts are not sure why. Among a plethora of discarded theories - including greys interfering with the mating behaviour of reds, and physical attacks - the likely reason is more prosaic. Greys are more efficient at using resources. In other words, they claim a competitive edge over our British Nutkin.

Greys are better adapted than reds to living in broad-leaved woods, in mixed conifer/broad-leaved plantations, in parks and in urban areas, simply because they are more efficient at exploiting the food resources available. For instance, in oak/hazel woods, greys eat - and more efficiently digest - acorns from the oak trees and nuts from the hazels while reds confine themselves very largely to hazelnuts.

Reds, though, are better adapted to conifer-only plantations, where they feast on the cones that carry the seeds of pines and spruces. Greys are less partial. But if the plantations contain groups of broad-leaved trees - beech, oak and sweet chestnut, for instance, all of which produce large and tasty seeds - then greys have the variety of food they are so adept at exploiting.

Ironically, such broad-leaved trees are often introduced to diversify the conifer plantations' otherwise poor habitat value, increasing markedly the plant and animal species it will then support.

Given such wildlife-enhanced plantations, the ever adaptable greys can exploit the conifers when they produce cones, and acorns, beech mast, chestnuts and hazelnuts when they do not. Reds, it seems, stick to the conifers, something borne out by observations made by Sarah Cartmel, who is studying the seasonal use red squirrels make of conifer plantations at Clocaenog Forest in North Wales. Funded by the Countryside Council for Wales and Forest Enterprise, she has found that reds favour Scots pine and larch in winter - provided they have produced plenty of cones - Sitka spruce in the autumn, and Norway spruce year round. 'Reds still seem to be more abundant in Clocaenog than greys,' she says. 'But there are pockets of greys, particularly where any broad-leaved trees occur or around picnic sites.'

The reds' limited menu may mean that they deplete their all-important winter natural fat reserves, lose weight and become more vulnerable to cold and infections. Survival and reproduction rates fall. According to Gurnell and Pepper, this may explain their decline in the 20,000 hectares of Thetford Forest in East Anglia, despite enduring their grey cousins for more than 20 years.

Based on these and other findings, they have developed a strategy for trying to retain red squirrels where they still survive. Eliminating or even stopping the inexorable northward spread of greys is impossible. So red squirrels can be retained only in pockets of forest where greys can either be controlled - by shooting or poisoning - or where reds can be favoured, such as by artificially feeding them from hoppers that the larger greys cannot get into.

Most, if not all, of these pockets will be conifer plantations. Retaining them in larger areas of countryside - including broad-leaved woodland - may be worth a try but will not work unless the numbers of greys are relentlessly, and effectively, controlled.

In conifer plantations the number of conifer species may need to be increased to improve the chances of cone crops at different times of year. Broad-leaved trees, particularly those such as beech and oak, which produce large seeds, need to be felled, a strategy that will not reduce the population of small mammals such as voles but that will certainly do nothing to increase flowering plant and bird species diversity. Smaller-seeded broad- leaves, such as rowan and willow, can be planted instead, as these encourage birds such as nuthatches and bramblings.

Gurnell and Pepper have gone a step farther and proposed a design plan for the ideal red squirrel forest, incorporating details such as its shape (round is better than long and thin) and diversity of tree age.

Crucial to the plan is a buffer zone around the forest to discourage greys from gaining a toe-hold. It should be about 3km wide, preferably more, and can consist of pure conifer plantation or open land devoid of any woodland. If it was devoid of all trees and hedges, it would be even more effective, emphasising again the contrast between red squirrel needs and those of wildlife generally.

Reintroducing red squirrels into forest from which they have been lost will be, at the very least, an uphill struggle. A feasibility study using release pens, food hoppers and red squirrel nestboxes is under way at Thetford, in a project managed jointly by the Forestry Authority and English Nature. To increase the red squirrels' competitive edge, the number of greys is having to be controlled.

Grey squirrels are not solely a problem for Beatrix Potter's ruddy little story character. They gnaw the bark off young broad-leaved trees, a major disincentive to planting them throughout much of England and Wales. In urban areas they sometimes take a fancy to house lofts, gnawing power cables and starting blazes for good measure.

These are problems we may even end up exporting to a European continent where greys are virtually unknown and perky little red Nutkins still reign supreme. While it is highly unlikely that greys will ever run the length of the Channel tunnel - which, in any case, has built-in anti- fox measures (to guard against rabies) - hitching a ride on cargo lorries is not impossible. Harry Pepper suggests that the occasional appearance of a grey squirrel on the Isle of Wight - still a reds-only stronghold - is probably the result of a grey taking a lorry ride across on the ferry.

Perhaps the demise of the red squirrel is inevitable, a painful lesson to be learnt from the unthinking introduction of a non-native species, however inoffensive it may at first appear. But conservationists have not given up yet. Not by a long way.

(Photograph omitted)