2.5 million shades of grey

Tom Wood
Tom Wood

The Grey Squirrel. We see it everywhere, all through the year, in all weathers. It’s one of the first bits of wildlife we are exposed to as children and one of the earliest ones we learn to name.

But of course the grey squirrel is most definitely not a native of these shores. They were introduced in 1876 from north America as interesting features in big estates throughout the UK, and now around 150 years later there are over 2.5 million of them!

In contrast our native squirrel, the smaller and lighter built red squirrel, has dwindled to a population of around 10,000-15,000, isolated in Scotland, Cumbria, parts of Northumberland and the Isle of Wight. Yes OK, the grey squirrel could easily be regarded as ‘cute’ with its fluffy tail and chittering call, but there any fluffiness surely stops, for behind the twitching curled tail they are hugely damaging to tree and bird populations.

Trees decay and die through having their bark and cambium chewed away; these are the outer layers of the tree that the tree needs in the transport of nutrients and in protection from disease. If the squirrel removes these layers right around the tree, everything above dies. It seems likely that the squirrels do this to obtain something (maybe sugars) from the tree, but there may be other reasons. During the breeding season squirrels squabble and fight and it is thought that this is when much of the damage to our trees occurs; frustrated young squirrels, losers perhaps in the game of squirrel love, take out their aggression on the trees.

All this damage to trees amounts to millions of pounds lost in woodfuel and timber production, as well as much wasted money when replanting or planting new woodlands. It also creates potential hazards in the form of decaying branches in public places, not all of which are easy to see from the ground. By damaging young trees, the grey squirrel is actually a threat to the continued survival and regeneration of our broadleaved woodlands. In the interests of fairness I should also point out that squirrels do have a role in woodlands managed for wildlife, namely that they move seeds and acorns around the woods and helpfully bury them ready for germination (though the red squirrel also does this). The damage to trees they cause also has a role in creating young ‘veteran trees’ with rot, holes, natural fractures and other habitats which can be usefully exploited; however overall their impact on woodlands is not a positive one.

The grey squirrel also loves eggs and bird chicks to supplement its tree and nut based diet, and may cause significant losses to our already beleaguered songbirds. I have witnessed a squirrel helping itself to bird eggs whilst the parents shout from a nearby bush, and have found the remains of empty dormouse nests outside my nest boxes which appear to have been chewed open by a hungry squirrel.

So, what we have here is a classic picture – an introduced species succeeding in its new environment, but at odds with and out of balance with everything else, in a way in which our native red squirrel is not. So what could we do about it? One promising and interesting option is the reintroduction of another species pushed out of most of the UK by human activities, and thereby opening the door for grey squirrel expansion- the pine marten.

The pine marten is a pretty little animal of the mustelid family (stoats and weasels) which is very much at home in woods and is brilliant at climbing trees. It also loves squirrel for tea. The pine marten was once found across the UK and it is thought there could have been around 150,000 of them at one time, but its numbers were severely curtailed in the 18th and 19th Centuries, mainly due to woodland clearance and the expansion of pheasant shooting (because reared pheasant is a very agreeable but dangerous food for Martens).

The pine marten has in recent years staged a bit of a natural comeback and the interesting thing from our perspective is that studies have shown that where the marten flourishes, the grey squirrel suffers and the red makes a comeback. The grey squirrel is bigger, heavier and feeds more on the ground than the red, and appears to be delicious. I’m not suggesting a marten wouldn’t eat a red if it got the chance, but being smaller, lighter and able to evade the marten up in the trees as well as, crucially, having evolved alongside each other, this happens far less than it happens with greys.

So is that it? Is the pine marten our silver bullet for the grey squirrel? Well probably not, though it can’t hurt to try and bring a bit more balance back to our countryside. What else could we do?
Up until recently squirrels could be controlled through the use of Warfarin in baited hoppers, though this has recently been banned due to the likelihood of dispensing Warfarin to unintended species using this delivery method. So we are left with live catch traps and shooting. Incidentally whilst it is perfectly legal to use live catch traps to control squirrels, they should by law be checked very regularly and the squirrels dispatched humanely. This does indeed function to remove squirrels, but it is very labour intensive and costly and most importantly, you can never stop!

As squirrel populations around the area you are trapping in drop, more squirrels move in, so unless all your neighbours help out you can find yourself footing the bill for the entire area! Coming on the market soon is a device designed to help, the interestingly named Goodnature trap. This is mounted on a tree and is baited with an attractive paste type substance. The squirrel sticks its head inside to get at the bait and a gas-powered captive bolt kills it instantly. The bolt retracts, and the squirrel drops to the ground and the trap is ready to go again. This makes the job of squirrel control much simpler and cheaper, although to be truly effective it is thought you need 1 trap per hectare to begin with, and each trap will cost around £150!!

Probably the most exciting piece of work currently going on in the world of squirrels is chemical contraception. Unsurprisingly when the great British public were asked whether we should trap and kill squirrels or prevent them breeding to control their numbers the latter option was much more palatable. New fields of work involve delivering these contraceptives orally using SPECS. SPECS (SPoropollenin Exine Capsules) are basically pollen grains with the contents emptied out and the empty shell filled with whatever you like, in this case a contraceptive.

This allows the contraceptive to survive long enough in the gut to be effective. Work is being undertaken on how much of these SPECS a squirrel must ingest to create the desired effect, but if squirrels could be fed contraceptive early in the year before breeding, perhaps in a carefully designed feed hopper already under development, then we could prevent breeding for 1 or more years. Done continuously over many years, this should surely have the effect of thinning out the population somewhat.

So the message is, there is hope, hope for our red squirrels to return, hope for more pine martens, hope for millions of trees and the survival of songbirds, and hope that before too long our woods won’t be filled with 2,500,000 shades of grey.