There are thought to be more than 2 million grey squirrels, which outnumber the reds by 66 to one. In a departure from normal planting methods, the Forestry Commission is not going to grow any more oak trees in Europe's biggest managed conifer forest after computer modelling carried out by Newcastle University and Queen Mary and Westfield College, London, shows how the grey squirrel is pushing the red to the brink of extinction.
The red squirrel migrated to Britain 10,000 years ago during the last Ice Age. Since the grey was brought over from America in the 19th century, the red has steadily declined. Explanations for this range from mating with the reds to produce infertile offspring to aggression. "These theories have been discounted," says Dr Peter Lurz, part of the team at Newcastle. "The greys don't beat up the reds. The two species ignore each other. And there is no influence on mating."
Research has shown that the main impact is during the juvenile stage. If reds live in an area that becomes infiltrated by greys, they normally disappear after about two years as the adults die and young reds are unable to colonise the area. One reason is because the grey is well suited to this country: they prefer broad-leafed trees, like oak, since they are similar to their native hickory habitat, and are better able to digest tannins in seeds like acorns. In contrast, the reds are better adapted to conifer forests containing trees like the Scots pine.
The reds have been reduced to between 20,000 and 30,000 animals in southern Britain. About 4,000 are found in small pockets in Wales, Thetford Forest in East Anglia and islands off the South Coast, such as the Isle of Wight. The only large remaining area suitable for red squirrels, which contains the remainder of the species, is Kielder Forest in Northumberland and north Cumbria. However, grey squirrels are encroaching from the north, from the Border Counties as well as from the south. Kielder Forest, which spreads across 50,000 hectares, is likely to be one of the last strongholds of the red squirrel in England.
If the reds only faced competition for food at the juvenile stage, it is unlikely they would be at such a critical junction. Back in the late Seventies Dr Jonathan Reynolds, now a research scientist at the Game Conservancy Trust in Hampshire, was studying red squirrels at Thetford Forest, in an attempt to understand why the species was faring badly. He concentrated on their feeding behaviour: greys are 60 per cent bigger than reds and he thought this might increase the competition for food. His study population kept dying of a myxomatosis-like disease yet there was nothing obviously wrong with the animals. Dr Reynolds supplied carcasses to Norwich University's Veterinary Investigation Centre. After 20 routine post-mortems had been carried out, the vets realised that this was a far more complex situation and sent the next batch to Maff (now Defra), whose scientists discovered that the squirrels were infested with an unknown virus.
After 20 years we now know that the grey harbours the parapox virus, which is benign to this species. "It is most likely that the grey squirrels brought the virus with them from the US," says Tony Sainsbury, from the Institute of Zoology, Zoological Society of London. It is possible that the virus is carried by fleas that live on the grey, which red squirrels pick up when they use the dreys, or nests. What we do know is that the virus acts swiftly - within 15 days, reds suffer from inflamed skin around their eyes and toes that develop into lesions. The disease is almost invariably fatal, although no one knows if the virus kills them or if they die of hunger and a low immunity.
Recent research by the Newcastle and London team has highlighted the interplay between disease and food competition. In places such as Italy and Scotland where the greys don't have the virus, the reds decreased by about 4 sq km a year. In Norfolk and Cumbria, where the greys are disease-carriers, the reds retreated at a rate of 90 sq km a year. As a result of this work, Dr Lurz and Professor John Gurnell from Queen Mary College, London, suggested that the Forestry Commission should manage Kielder Forest in a pro-red squirrel way. Previous plans to plant corridors of oak trees would be the equivalent of building motorways along which grey squirrels would migrate to wipe out the native species. The Forestry Commission will continue with some native woodland planting though, as well as "squirrel-neutral" species such as birch, rowan and willow.
Unfortunately, Dr Reynolds is not convinced that this will work. "You have to take into account the size of the army of reds and greys. The advancing greys may be existing on a sub-optimal diet but this doesn't matter because they will be replaced by an army that keeps on coming. The reds, even eating an optimal diet of Scots pine, will be undermined by disease and will disappear."
Dr Reynolds ended up charting the demise of the red and the infiltration of the greys for his PhD. Dr Lurz used this data, as well as satellite imagery of ranges linked to the forest's new design plans, plus 10 years' worth of research on radio-tracked squirrels. The team used this information to help them model the potential spread of the disease as the greys invade Kielder forest. They have shown that if the greys invade, as they surely will, they will march on Kielder using four wooded routes into the forest. "There will be local extinctions," says Dr Lurz, "Hundreds of reds will die."
Dr Lurz doesn't think it will be the death of the species though - because the greys can only access Kielder along these four highways, there is some hope that overall the reds might be able to survive. If his theory is correct, the reds will become infected as they make contact with the greys, and will infect their neighbours, all of whom will die. But assuming that the squirrels die within two weeks and do not travel far during this period, it is unlikely they will infect more squirrels than those in their immediate home ranges. "Overall it's a positive message," says Dr Lurz.
It doesn't sound like one. The Government has now suggested that greys should be culled in and around sensitive areas, such as Kielder; the greys would be exterminated by being shot or poisoned. Dr Lurz does not support a cull himself, saying, "I personally feel that one cannot carry out this kind of control over five to 10 years."
The European Squirrel Initiative is in favour of the cull but its spokesman, Andrew Kendall, says, "Our view is that this is not a sustainable objective. No matter how hard you try, the greys will get through your defences; culling will only buy you time to safeguard the squirrel gene pool." Instead, the ESI is in favour of developing a species-specific contraceptive. Dr Reynolds is sceptical, pointing out that Australia has spent millions of dollars attempting to create fertility control for rabbits. Not only have the Australians not managed, but none of the chemicals developed would pass environmental health standards. "I think we need to know a lot more about this disease," says Dr Reynolds. "We need to have a test for it, we need to be able to screen populations, which will change management plans, and we have to hope that a vaccine will be developed."
Others have put their faith in captive breeding programmes, such as the one at Kelling Heath, Norfolk, which is part of the national breeding programme. The Independent has previously reported research by Dr Lurz, which showed that a new strain of Cumbrian red squirrel had been detected. At the time, Dr Lurz said that this strain should be included in the programme, adding, "A captive breeding programme needs to be introduced as an additional conservation measure, just in case the conservation programme does not work. This will guarantee these unique animals are not lost forever."
Unfortunately, there is no chance that any of the red squirrels, Cumbrian or otherwise, could currently be released on mainland Britain as they would succumb to the virus. Although Dr Reynolds thinks the situation is "pretty bleak", Professor Gurnell is more positive: "I'm optimistic that in some places, such as the north of England and Scotland, red squirrels will persist."
Sanjida O'Connell is the author of 'Sugar: The Grass that Changed the World' (Virgin Books, £8.99)Reuse content