A VIRUS carried by the grey squirrel kills the native red species up to 25 times faster than competition for habitat, a study shows.

The finding prompted calls for selective culls of grey squirrels to be carried out to protect the remaining red population.

The disease, squirrel pox virus, is so deadly to red squirrels that they are likely to die out in England within a decade unless the spread can be halted.

Scotland had previously been clear of the disease, but confirmation of a case this year means that red squirrels north of the Border are equally at risk.

Scientists already knew that both the virus and habitat competition from grey squirrels had caused a decline in the population of the reds, but the study by teams from Newcastle, Queen Mary, London, and the Zoological Society of London (ZSL), proves which is the main contributory factor.

Peter Lurz, of the University of Newcastle, said: “It is vital we get this disease under control. We are not trying to wipe out the grey squirrel but as conservationists we have a duty to look after the red squirrel as it is a protected, native species.”

Computer modelling has shown that a general cull would be impractical. Dr Lurz said the best method of control would be to trap grey squirrels as they approach the habitats of red squirrels.

The technique has been tested in the Kielder Forest, Northumberland, where greys can reach the forest only along a limited number of routes because they will not travel long distances across open ground.

However, Professor Stephen Harris, of Bristol, is one of a number of academics who questions the measure, arguing that culls have met with so little success that conservationists should accept that trying to save the red squirrel is a lost cause, with the exception of island populations that are protected by water. He said that the money should be directed to other projects where the chances of success were higher.

Tony Sainsbury, lecturer in wild animal health at the ZSL, disagrees. “The cases seen by ZSL’s national red squirrel disease surveillance programme clearly demonstrate the debilitating nature of the squirrel pox virus disease on red squirrels. Given that the grey squirrel is an introduced species, and therefore the disease has occurred as a consequence of human action, the onus is very much on us to look for practical solutions to control the disease and protect red squirrels.”

Decline of native

• Red squirrels were widespread throughout Britain until the introduction of the grey squirrel from North America in the 19th century
  
  
• Red squirrels now have English strongholds only in Cumbria, Northumbria and North Yorkshire
  
  
• Research has shown that squirrel pox virus is the most important factor pushing them towards extinction. By measuring population decline, scientists have calculated that the virus speeds up the rate at which red squirrels are driven out by 17 to 25 times
  
  
• About 70 per cent of grey squirrels have been exposed to the virus, but it does not appear to harm them. Red squirrels usually die within a fortnight of exposure

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