Curtailed; Will Contraception Spell the End of London’s Grey Squirrels?

© Bertie Gregory 

Our Director of Conservation, Mathew Frith looks into the Government’s plans to control and eventually eradicate the grey squirrel from Britain

I recall a grey squirrel control training session some 25 years ago, and being told that the measures we were shown – the use of bait laced with warfarin - might be useful for protecting trees on a small site, put pointless across the wider landscape. A toxic blood-thinner, warfarin sounded simply noxious, especially as it couldn’t prevent the poisoning of other animals.  Therefore, the Government’s announcement last week (26th January) that they would support a programme of contraception to control and eventually eradicate grey squirrel from Britain raised many eyebrows, and caused me to cast a wry smile.

Its justification was wrapped in that usual nutshell of the impacts of invasive (read ‘non-native’) species on the British economy, an estimated £1.8 billion annual cost. Lord (Zack) Goldsmith said that the damage from grey squirrels also threatens the effectiveness of government efforts to tackle climate change through its tree-planting programmes to create “tens of thousands of acres of new woodlands.”  The programme has the support from the Prince of Wales, who helped co-found the UK Squirrel Accord with the objective of "managing the negative impacts of invasive grey squirrels in the UK", along with a range of forestry, conservation and research organisations, including The Wildlife Trusts.

The proposal, following a pilot trial in Yorkshire, involves luring grey squirrels into feeding hoppers only they can access, containing little pots of hazelnut spread laced with an oral contraceptive.  Results of studies so far suggest that in a small wood only a few days is required in summer to ensure the majority of grey squirrels access and consume the food that will ultimately contain the contraceptive. This non-lethal fertility control, ethically sounder than the other measures used so far, is currently subject to further research to assess its effective roll-out. 

Grey Squirrel

© Bertie Gregory

Grey into red, becomes grey

There is no doubt that grey squirrel has had a profound and negative impact on Britain’s red squirrel populations. Originally introduced here in the mid-1870s from the eastern coast of North America[1], its catholic diet, habitat adaptability, fecundity, and lack of significant predator pressure, has long given it a competitive edge over red squirrel, already vulnerable from habitat loss.[2]  Legislation, first enacted in 1937 to prevent its further introduction into Britain, has been a classic case of ‘horse, open door, bolted.’[3] The grey squirrel also carries a virus, squirrel pox, which is almost always fatal to red squirrels. Grey squirrels rarely contract the disease, but can transmit the virus in high concentrations to reds when the populations mix; an outbreak can wipe out the majority or all of a local population of reds.  Research shows red squirrels die out 17-25 times faster than by competition from grey squirrels alone.

Squirrel pox’s fatal spread into red squirrel populations is linked to grey squirrels entering areas where red squirrels live.  It is through this that the grey squirrel’s spread northwards has been at the loss of the red, at a rate that suggests that the latter would be extinct from much of Britain by 2030.[4]  As such conservation efforts over the past 20 years have tried to prevent grey squirrels getting close to the populations of reds, predominantly those in north of England and Scotland.  Traditional methods of control, usually used to prevent damage on timber trees, such as shooting, trapping, and poisoning[5], are expensive, arguably inhumane, and at a landscape scale, largely ineffective without co-ordination of landowners.

Isolated populations of reds still exist in parts of England; Formby, Thetford Forest, Brownsea Island, and the Isle of Wight.  All these are monitored by a cordon sanitaire to prevent greys getting close.  There have been hopes that pine marten introductions and their recolonisation in England might play a part, as martens find grey squirrels easier prey than red. However, their impacts are likely to be only marginal, as research suggests that martens avoid the greys’ strongholds, our towns and cities.

If the contraception programme takes off, then it offers a much better chance to sustain our red squirrel populations, and will rightly be prioritised at those in northern England and Scotland. Here the greys will need to be eradicated and their potential interaction with reds steadily pushed back to create more and more space for red squirrel populations to recover and return to their previous strongholds in northern and upland England and Wales.

Red Squirrel

© Peter Cairns

What will this mean for London’s grey squirrels? 

The grey squirrel’s first recorded introduction in London was 100 individuals in Richmond Park in 1902[5], which sparked a spate of further successful introductions in the following decade. By the 1930s they were already well-established (and culled in large numbers[6]) as there was little competition and no predators. Red squirrels were already rare (having been largely decimated in southern England by an epidemic in 1900), with only a few populations holding on in Epping Forest until the 1960s (no doubt with the help of some sharp-shooters).  For some of us, red squirrels only survived as a symbol of road safety.[7]

The grey squirrel is ubiquitous throughout London. Whilst their numbers exert some pressure on some other animals (occasionally taking fledglings, for example) and they will strip bark from trees (ash, sycamore, and beech are favoured), their impacts are minor compared to the other pressures nature faces here.  Some ‘control’ (aka culls) does take place in some parks and private land, but usually out of sight given the sensitivities this can cause. Any attempts to visibly drive a reduction in grey squirrels here by lethal means would be highly controversial, and counter-effective.

For the grey squirrel is the one wild mammal most people get to see readily and engage closely with if they wish to in London.  Watching people feed them in parks demonstrates the draw they have.  Yes, maybe their ‘cute and cuddly’ appearance disguises their more damaging traits, but in London we surely must recognise how the grey squirrel acts as a potent portal into the wider world of nature conservation, whether it’s how our parks are managed, or what we need to do to enhance our woodlands.  It is both an example of the multiple origins of the city’s ecology, and the complex issues this can cause. 

It is not without irony that Britain’s red squirrel population is not as indigenous as it seems.  This irrefutably attractive mammal was once seen as a pest and persecuted for centuries, and then often topped up with animals from elsewhere in Europe (including those in Epping Forest in the early 20th century).  Some ill-advised attempts at re-introducing red squirrel into London have all failed.  They will continue to fail whilst the greys are present. Nevertheless, it is our native squirrel and at one time lived in and around London, although at very much lower densities than the greys currently enjoy. 

If the contraception of grey squirrels proves a success and proceeds, then the focus will be need to be where the reds are most threatened.  This isn’t around London, but – if red squirrel populations recover long-lost territories – it just may become an interesting nut to crack in years to come.  Will Londoners be prepared to support the replacement of a brazen, but very watchable squirrel, for another that hasn’t been here for almost a century, and to play a part in this?[8]  As it will undoubtedly need our collective efforts in placing that laced hazelnut spread in feeders to hoodwink the greys into their own eventual demise.

Mathew Frith, Director of Conservation

[1] There were sightings from the 1830s in Wales from escaped individuals.

[2] The relationship between red and grey is complex, and our own impacts on red squirrel (in addition to introducing the grey) in Britain can’t be excluded (see references).

[3] Grey squirrel is listed on Schedule 9 of the Wildlife & Countryside Act 1981 making it illegal to release one into the wild. This poses dilemmas for wildlife hospitals which are brought orphans or injured animals.

[4] There are approximately 140,000 red squirrels and 2.5 million grey squirrels in Britain.

[5] Prohibited in areas where red squirrel are present.

[6] An introduction of five animals in Bushy Park in 1889 failed.

[7] For example, 4,000 shot between 1917-37 in Kew Gardens, and 2,100 shot in Richmond Park 1932-37.

[8] Tufty Fluffytail was a mascot the of the Royal Society for the Prevention of Accidents, used to inform millions of children on road safety from the 1950s-1990s.


Laidler, K, 1980. Squirrels in Britain, David & Charles, London.

Harris, S., and Yalden, D. 2008, Mammals of the British Isles, Handbook, 4th Edition, The Mammal Society, London

UK Squirrel Accord  (accessed 1st February 2021)