Maxwell Amenity's Technical Manager, John Handley, looks at the UK's growing grey squirrel population and asks whether it is ever going to be possible for them to fit harmoniously into the natural ecology of the British Isles
We've just been scolded by an indignant squirrel. It's October, the days are noticeably shorter and my daily amble with Sidbury, a loping Labrador cross Collie, is broken by his confusion as the rabbit he thought he was chasing dashes up the trunk of an oak tree, along a bough, skitters through the branches, leaps onto a neighbouring beech tree and comes to a halt on the trunk of the beech, where it berates both Sidbury and I with what could pass for a stream of expletives.
In common with many people who feed garden birds, I have a love/hate relationship with squirrels. I admire their agility, dexterity, intelligence and ability to live successfully alongside people. I'm duped into seeing their bright-eyed, bushy-tailed demeanour as appealing and, dare I go as far, as 'cute'? But they epitomise the quandary we face as naturalists when we shoulder the responsibility as temporary custodians of our countryside. They engender uncomfortable feelings of status, even race, colour and where we draw the line when it comes to looking after what is ours.
The language used around grey squirrels is loaded: non-native, alien, Greys vs Reds, talk of culling, trapping, vermin, tree-rats, long-term contraceptives and vaccinations. What did they do to earn such condemnation?
The grey squirrel (Sciurus carolinensis), was introduced into the UK from America. The first documented release was at Henbury Park in Cheshire, although the most significant release was in Woburn Park, Bedfordshire in 1890. Up until that point, the only squirrel in Britain was the Eurasian red squirrel (Sciurus vulgaris), which had made its way here after the glaciers retreated around 8,000 years ago, and the North Sea and English Channel cut us off from Europe, awarding the red squirrel the status of 'native'.
This doesn't mean that it has always been considered favourably: both red and grey squirrels strip the bark off trees to get at the sugary sap, and also eat the fungi that grow underneath. Removing bark is also a method of marking territory, and squirrels use the bark to line their nests, which are of two types, a cavity within a tree and a drey, which is an assemblage of twigs within the fork of two branches. The damage that this does to trees has cost the Forestry Commission more than £10m.
Although now protected and currently on the International Union for Conservation of Nature's (IUCN) Red List of Threatened Species, as a species of least concern in the 19th and 20th centuries, the red squirrels were heavily persecuted and pushed to the brink of extinction throughout the UK. Shooting clubs were set up to eradicate red squirrels, their tails were kept as proof to redeem bounties. Right up until 1946, the Highland Squirrel Club paid out £1,504 to members of up to 56 estates. It was considered to be such sport, and numbers of squirrels had dropped to such an extent, that it was necessary to reintroduce them from other areas of the country and from countries such as Sweden.
Since their release in 1890 at Woburn, grey squirrels quickly naturalised and, in the absence of competition and with predators also being supressed, the population exploded - by 1930, the population covered 25,693 km2 and, five years later, this area had nearly doubled.
The impact of this spectacular growth in numbers resulted in The Destructive Imported Animals Act in 1932, making it illegal to import, keep or release grey squirrels. Propaganda was produced promoting the control of grey squirrels: in 1936, twenty-six county councils distributed more than 5,000 posters entreating the general public to "kill the tree rat". In 1937, it was designated a pest because of the damage it did to trees and cereal crops and a bounty system was established to try to control the population.
In 1943, County War Agricultural Executive Committees issued free shotgun cartridges to registered grey squirrel shooting clubs to reduce their numbers (MAF, 1943). By the end of 1947, 450 shooting clubs had killed 100,000 grey squirrels. This had little effect. By the 1950s, the grey squirrel occupied the whole of central England and was still expanding its range by over 2,500 km2 per year.
By 1952, approximately 7,000 grey squirrel shooting clubs were in existence and, in 1953, the first anti-grey squirrel propaganda was broadcast on Radio 4's The Archers. An experimental bonus system was introduced to complement squirrel clubs; one shilling or two free cartridges paid per grey squirrel tail. The bounty was raised to two shillings in 1956. 1,520,304 grey squirrel bounties were paid in five years with no effect on their numbers. This system was abandoned in 1958 when it was demonstrated that trapping was more efficient than shooting them.
Where grey squirrels have been increasing both in terms of numbers and their range, red squirrels have diminished. There are now over three million grey squirrels and less than 160,000 red squirrels, with some forecasts stating that the red squirrel will be extinct in the UK by 2031. The IUCN places the grey squirrel in its top 100 most invasive species.
Grey squirrels outcompete red squirrels for resources: whilst both species feed predominantly on seeds and fruit throughout the year, they are capable of adapting their diet to take advantage of the seasonal abundance of different foods.
Specifically, red squirrels eat acorns, berries, fungi, bark and sap tissue; soil and tree bark are also eaten, probably for roughage and minerals.
Grey squirrels will eat mast (mast is the fruit of forest trees such as oak and beech), tree shoots, flowers, samaras (the key seeds of the field maple and sycamore), nuts, fruit, roots, cereals and sap tissue. Both species occasionally eat insects, eggs and young birds from nests although, on a larger scale, squirrels are not thought to be significant predators of avians. Grey squirrels will scavenge leftovers, eating southern fried chicken and ice cream cones from bins, as well as raiding bird feeders.
Red squirrels spend most of their time in the canopy and only around a third of their time on the ground, whereas the grey squirrel spends almost all of its time foraging on the ground. Grey squirrels will also eat food before it ripens, quite literally beating the red squirrels to the resource. Grey squirrels put on more weight enabling them to go into the winter in better condition, giving them more chance of surviving periods of scarcity.
Mortality rates vary between species and populations, and are strongly correlated with the mast crop, with greater numbers of squirrels surviving after a good mast year.
Predators include foxes, cats, pine martens, dogs, owls, buzzards and goshawks, whilst stoats, weasels, mink and snakes will take kittens (young). Starvation is a significant threat, but the most substantial threat is being hit by vehicles, with mortality of 78% in some incidences where feeders lure squirrels into gardens across busy roads.
The grey squirrel is also a carrier of the Squirrel Pox Virus, to which the grey squirrels are generally immune, but red squirrels are fatally susceptible to within two weeks. By 1979, red squirrels were regarded as highly uncommon, with diminishing populations amidst a sea of grey squirrels.
The red squirrel is now a protected species under the Wildlife and Countryside Act 1981. Brownsea Island in Dorset, and Anglesey off the north-west coast of Wales are examples of areas within the UK where the forests are being managed to support red squirrels and the grey squirrel is actively culled. The grey squirrel is being demonised by the red squirrel lobby.
Beatrix Potter's creation of Squirrel Nutkin, published in 1903, has been used to transform the fate of the red squirrel from bane of the foresters' life to national emblem, but it has also been used to define a peculiar form of 'Englishness', alongside red telephone boxes, warm beer and cricket bats.
During an impassioned squirrel debate in the House of Lords, Lord Inglewood of Cumbria identified the red squirrel as the most "lovable and loved of our British native animals". He even urged celebrity chef Jamie Oliver to promote eating grey squirrels in his campaign to revolutionise school meals. Lord Redesdale, whose seat is in Northumberland, where a population of red squirrels is present, agreed, declaring "if you can't beat them, eat them" and has founded the Red Squirrel Protection Partnership whose mission is simply to "kill grey squirrels"
In another debate in 2006, Lady Saltoun of Abernethy pronounced the red squirrels innate superiority over the grey squirrel. Cloaking reds in the admirable qualities of a better class of person, she observed that they are "rather like quiet, well behaved people, who do not make a nuisance or an exhibition of themselves, or commit crimes, and so do not get themselves into the papers in the vulgar way that grey squirrels do". Media coverage of this has been cited as the cause of anti-Americanism.
A paper published in 2014 indicates that the presence of the native European pine marten (Martes martes) has a positive correlation with the population crash in the Irish Midlands of the grey squirrel, whilst the native red squirrel population is increasing in these areas. It is thought that the red squirrel, being smaller, can escape to the furthest branches, whereas the grey squirrel falls victim to the attentions of a native predator.
We are beginning to understand that ecosystems are complex structures and predators such as pine martens have a place; by eradicating them from an area, we upset the natural balance that has been achieved over time. By introducing non-native species, we also upset the balance. In the long term, the grey squirrel may be the nail in the coffin of the red squirrel, it may only be a temporary guest or it may come to share, equitably, a place in our landscape. Whatever happens, they will always have a welcome at my bird table and I'll always be amused at the look of bewildered consternation on Sidbury's face.
BASC Grey Squirrel Control
Since their introduction into Britain in the 1870s, grey squirrels have spread rapidly. They have displaced the red squirrel throughout most of England and Wales and in southeast and central Scotland.
Grey squirrels can cause serious problems for foresters, native wildlife and gamekeepers. The bark stripping from tree trunks, during the months of May and June, damages stands of timber and natural woodland.
In spring, the taking of eggs and young chicks can be devastating for songbird and ground nesting bird populations. Damage to hoppers, feed bins and water pipes can cause serious and costly shoot management problems.
The grey squirrel is also a significant factor in the decline of the native red squirrel population in the UK. Greys can carry the squirrel pox virus. And, although they are relatively unaffected themselves, the disease causes considerable suffering and death to the red squirrel - which is already severely threatened and extinct in many parts of the UK.
Grey squirrels have limited legal protection and can be controlled all year round by a variety of methods including shooting, trapping and poisoning. It is an offence under section 14 of the Wildlife and Countryside Act (1981) to introduce and release grey squirrels into the wild.
Under the provisions of the Animal Welfare Act 2006, any person using a squirrel trap, would only be responsible for any animal caught by it, but not its offspring still in the wild. Under the act, it is an offence to cause unnecessary suffering to a kept animal (this includes live caught animals).
Methods of Control
At different times of the year, the control of squirrels can take different forms. With the leaf off the trees, winter is a good time for shooting.
Drey poking can be effective, especially on cold winter days. A team of four, with two working the poles and two covering the tree can spend a day clearing a lot of dreys in a wood. When all the dreys are cleared from a wood in winter, it becomes easy to spot new ones made in the summer.
There are a few rules you must adhere to when carrying out this activity. Safety is paramount; guns should stand well back from the tree.
When using the poles, tap the bottom of the drey gently, this will allow the squirrel to run out slowly, it will probably stop just outside which will give the guns time to shoot. Never shoot at a squirrel running down a tree, it is better to either let it run down and run away from you or stop it and turn it back up the tree. Remember you are aiming to cull squirrels, so be efficient and effective.
This method is only one part of a fully effective control programme, as grey squirrels killed at this time of the year will often be replaced by others before the summer.
Tunnel trapping using spring traps
Spring traps are a very useful tool in catching squirrels. Set correctly these traps will effectively catch squirrels moving between trees. Look for the signs of squirrel movement, a common sight is the flat circle around the base of the tree where squirrels run around sometimes chasing each other.
The law and best practice requires you to:
Use the appropriate approved spring trap for your quarry.
Enclose your trap within a natural or artificial tunnel
Firmly anchor your trap
Check your traps at least once a day
All traps should be set in accordance with BASC's trapping pest mammals code of practice.
Live cage trapping
Live cage traps, either single or multi catch, involve attracting squirrels to a trap with a bait (food). These can be used in the same way as spring traps. Set at the base of trees and covered with logs. It is best to pre bait these traps, leaving the entrances open so that the squirrels can run freely for a few days before setting.
The density of traps required depends on whether single or multi- capture traps are used.
Single traps should be spaced 75-125m apart, multi traps 150-200m apart, equating to one trap per ha. In areas where it is difficult to draw squirrels to the ground - for example, pine mixtures, or where traps are disturbed by badgers, deer or wild boar - it may be necessary to site traps on platforms on the trees.
Captured squirrels should be humanely destroyed by guiding them to one end of the trap, where they can be killed with an air rifle or the traps can be emptied into a sack and the squirrels dispatched through a swift, heavy blow to the head. Non target species should be released immediately.
Shooting of grey squirrels can be a very effective method of control, especially in early spring when young shoots are showing in trees. On a sunny day, grey squirrels will work in the outmost branches of a tree chewing the new shoots and can present an easy target.
A shotgun or powerful air rifle would be suitable for this form of control but remember, as with all shooting, assess your background before taking any shot. If in doubt, don't shoot. A rimfire rifle would be more suitable for shooting squirrels on the ground around the base of a tree where a safe backstop is provided.
The EU licence for the production and sale of warfarin as a grey squirrel bait ended on 30 September 2014. Manufacturers and stockists are no longer able to sell warfarin to control grey squirrels.
Disposal of carcasses
Unless you intend to eat them, all dead squirrels should be deeply buried or incinerated. Any carcasses showing signs of squirrel pox virus (scabs around eyes, nose, mouth and feet) should be sent to the Animal Health and Veterinary Laboratories Agency (AHVLA) for investigation. Gloves should be worn when handling potentially infected animals.
Information provided by the British Association for Shooting & Conservation www.basc.org.uk
Black squirrels are becoming an increasingly common sight because of a genetic mutation which stops their fur turning to grey and could make them more immune to diseases, scientists have found.
Researchers will study whether the faulty gene, which is also found in white blood cells, makes the black squirrel more aggressive, as it does in other species.
The mutation in pure black squirrels, which are no threat to greys and can mate with them, is inherited from both parents and has a piece missing which is involved in producing pigment.
This makes their fur remain black rather than develop white and orange stripes which gives grey squirrels their coat.
In grey squirrels, the pigment gene works by producing two hormones - one which turns a switch on to produce black fur and another which turns this off, so that white and orange can be produced - creating the stripes.
In black squirrels the missing piece of the gene means this 'switching off' process never happens and their fur remains jet black.
Helen McRobie, senior lecturer in Biomedical Science at Anglia Ruskin University, said: "If you look closely at grey squirrel hairs, they are not actually grey at all but are a combination of white, black and orange stripes. However, the hairs of black squirrels have no stripes; they are just plain black."
"Our research shows that one hormone turns the switch on to make black fur, and a different hormone turns the switch off to make orange and white fur."
"So in the grey squirrel, as the fur is growing, the switch turns on and off to make the stripes.
"However, in the black squirrel, because there is a piece of DNA missing, a piece of the switch is also missing."
"The first hormone that switches it on still works and black fur is made, but the second hormone that should switch off, actually switches on as well. The off switch fails and the black fur continues to grow."
The black squirrel is the same species as the grey squirrel and poses no threat to the variety. Black squirrels can mate with greys and, if this happens, offspring will have a combination of faulty and fully working genes, giving them a brown-black coat.
There have been around 6,100 sightings of black squirrels living in the UK.
Both are a threat to the red squirrel and can carry a pox which can kill reds and damage trees.
McRobie, who leads the black squirrel project at Anglia Ruskin University, said she now plans to study the other effects of the DNA mutation to determine whether this helps the black variety survive by giving them competitive advantages.
It has been reported that the black mutations have more testosterone, making them more aggressive and attractive to females, but there is little current evidence to support this.
A similar mutation occurs in the black jaguar and McRobie predicts this is caused by the same faulty gene.
She added: "This gene is found in other places in the body. It is also found in white blood cells and could have other effects. It is not yet known how it is going to affect the squirrel. In some animals it does affect immunity and can make their immunity better."
The black squirrel was first spotted in Bedfordshire in 1912 and has been seen in South West England, Wales and Southern Scotland in the last two years.
Anglia Ruskin University's The Black Squirrel Project aims to gather data on the geographical range of the black squirrel within the UK.
Visit http://www.blacksquirrelproject.org/ for further information
British Broadcasting Corporation. (2006). Jamie 'must back squirrel-eating'. Available: http://news.bbc.co.uk/1/hi/uk/4835690.stm.
Broome and Johnson. (2001). An Evaluation of the Costs of Grey Squirrel Bark-Stripping Damage in British Woodlands. Forestry Commission.
Macdonald, D. and Burnham, D. (2011). The state of Britain's mammals a focus on invasive species. People's Trust for Endangered Species.
MAF. 1943. Memorandum to executive officers of County War Agricultural Executive Committees in England and Wales, destruction of grey squirrels: Grey Squirrels Order. MAF 44/45
Newson, S., Rexstad, E., Baillie, S., Buckland, S. & Aebischer, N. (2010). Population changes of avian predators and grey squirrels in England: is there evidence for an impact on avian prey populations? Journal of Applied Ecology.
Parliamentary publications. (23rd Jan 2008). Column 221 House of Lords. Available: http://www.publications.parliament.uk/pa/ld200708/ldhansrd/text/80123-0001.htm.
Rotherham, I. and Lambert, R. (2011). Invasive and Introduced Plants and Animals: Human Perceptions, Attitudes and Approaches to Management. London: Earthscan. p44.
Sheehy, E. & Lawton, C. (2014). Population crash in an invasive species following the recovery of a native predator: the case of the American grey squirrel and the European pine marten in Ireland. Biodiversity Conservation. 7 (23), 753-774.
The main article was first commissioned and published by Fair Acre Press for the Arts Council England funded poetry-writing project: Maligned Species http://fairacrepress.co.uk/projects/maligned-species-project/