Threats to Red Squirrels
Although red squirrel populations are healthy on mainland Europe, numbers in the UK have fallen from a one-time high, thought to be around 3.5 million, to a current estimated population of around 120,000. The population in England is thought to be as low as 15,000.
Grey squirrels were first introduced to England from North America in 1876 as an "exotic" species to populate the grounds of stately homes. Many separate introductions occurred until 1930 when the damage caused by the grey squirrel was recognised and it was made illegal to release a grey squirrel in to the wild. Grey squirrels have rapidly spread and colonised much of mainland England with devastating results for our native red squirrel.
Greys are roughly twice as heavy as red squirrels and can tolerate living in much denser populations and this, together with their voracious appetite and ability to eat nuts and seeds before they are ripe, gives them a strong competitive advantage over reds in mixed and broadleaf woodland.
The red squirrel is altogether more delicate in every way, lighter in weight and far more selective in its eating habits and only able to digest nuts and seeds when these are ripe. Traditionally, however, its one advantage over the grey squirrel has been the ability to live and breed in conifer forests.
By contrast, greys will travel through a conifer plantation, but there is insufficient food to make them want to stay. An unfortunate consequence of the recent trend of planting broad leaves for visual softening on the harder edges of conifer forests is that it allows greys a way in to the reds' terrain. Competition for food then becomes, once again, prevalent.
Failure to find enough food prevents female reds from gaining the optimum weight necessary for reproduction. In addition, existing members of the population can gradually starve. Through these effects of competition alone, greys could totally replace reds within 15 years.
Squirrel pox virus
The most significant threat associated with grey squirrels is the spread and transmission of a disease called squirrel pox virus (SQPV). As carriers of the virus, this does not affect them in any way or make them ill. But, it can take only one grey squirrel to introduce this virus to a local population of red squirrels and then the virus can spread throughout the reds with horrific effect.
Where a grey squirrel introduces SQPV, (and in this area approximately 75% of greys carry the virus) red squirrel numbers decline rapidly and up to 25 times more quickly than through competition alone.
A very small proportion of reds may have, or be developing, a natural immunity to the SQPV. A research programme, funded by The Wildlife Ark Trust, is currently working on the development of a vaccine. However, funding of a vaccine programme would be prohibitive in the current economic climate.
It is clear that, rather than doing nothing and risk losing this native and exquisite creature, we must pursue as many different avenues as possible to encourage and eventually ensure its preservation.
In order to buy time for the red squirrels, the only option available to us at the moment is to control and reduce the numbers of greys by trapping or shooting. This is particularly important in and around red squirrel strongholds if they are to have a fair and fighting chance of survival.