Shedding light on shades of grey (and red)

THE native red squirrel, once a common animal in many parts of the country, is under threat from the American grey squirrel which came here about 100 years ago.

Bushy-tailed red squirrels are already losing the battle for survival in England’s forests and a cull of grey squirrels has been announced in Britain to protect the red’s falling numbers.

Here, a national survey has just begun to find out the exact distribution of both species, and the public has been asked to assist.

Survey manager is Dr Michael Carey, of Combined Research and Inventory of Squirrels in Irish Silviculture (CRISIS). He believes the grey squirrel is not only a threat to our native red variety, but is also responsible for widespread damage to broadleaf trees through the removal of tree bark.

The grey squirrel was introduced to Longford in 1911 and quickly became established, gradually spreading out at a rate equal to about 3km per year. It can now be found in 23 counties, at least.

Expected to take six months to complete, the survey findings will be interesting, especially given the situation in Britain where, these days, a glimpse of a red squirrel is rare enough.

Our native red squirrels and their grey cousins are similar in many ways, being small tree-dwelling mammals using tree seeds, berries and nuts as their principal foods.

The grey squirrel, however, has a competitive edge as it can digest large seeds from deciduous trees, such as oak, before they are fully ripe. In this way, greys out-compete the red squirrels in mixed and broadleaf woodland, resulting in loss of condition and reduced breeding success of the reds.

Red numbers have declined so much that it is thought the species could be extinct in Britain within 20 years. We’ll just have to see what the survey reveals in regard to the numbers of both species here.

The culling policy has proved to be divisive among environmentalists and nature lovers all over Britain. While Biodiversity Minister Jim Knight accepts that many people love grey squirrels, he says the reality is that they are a real problem for some of the most threatened native species.

According to estimates, Britain has more than two million grey squirrels, outnumbering 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, showed how the grey squirrel was pushing the red to the brink of extinction.

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 put forward is that the grey is well suited to broadleaf trees, such as 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 with 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, East Anglia and islands off the south coast, such as the Isle of Wight.

Some novel methods of controlling the grey squirrel population are constantly being sought, including an innovative approach to contraception pioneered by Professor Harry Moore, of Sheffield University, a few years ago. The technique, known as immunocontraception, involved treating squirrels with a vaccine that would trigger the grey squirrel females’ immune systems to reject the males’ sperm, thereby preventing pregnancy.

Laboratory trials initially proved promising, with an immune response created in treated females.

The first trial showed a significant reduction in pregnancy rates among treated squirrels. But it was felt more research was needed for the work to continue and funding was not available to progress this work. Also very important is the lack of suitably managed habitat, a subject touched on by Dr Craig Shuttleworth, who is responsible for pioneering work involving the re-introduction of red squirrels in areas where grey squirrels are being culled.

“The work we are doing on Anglesey shows that red squirrels can be reintroduced providing grey squirrels are removed first.

“Over the past few years, we have carried out a policy of trapping and shooting grey squirrels to the position where there are now only a handful left. The reds we have introduced are thriving and the population will increase year on year,” said Dr Shuttleworth.

The questionnaire for the Irish squirrel survey is available online: www.Irishsquirrelsurvey.com.