As anyone in mainland Britain who has ever attempted to grow berries or nuts – or indeed feed the birds – will know, doing so is tantamount to an opening move in a game of chess with local grey squirrels, a game the squirrels tend to win. Grey squirrels are also partial to the occasional bird’s egg or fledgling, and enjoy stripping and eating the bark of young broadleaf trees, which can either kill the trees or leave them open to infection. This, quite apart from affecting biodiversity and landscape, harms the timber industry. The loss – in damaged timber, lost carbon revenue and tree replacements – is not insignificant: £37m a year in England and Wales.
Greys (Sciurus carolinensis), introduced from North America in 1876, have almost replaced native red squirrels (Sciurus vulgaris) by outcompeting their British counterparts for food and habitat. They are larger and more robust, and immune to squirrelpox, while reds are not. About 3 million grey squirrels now live in the UK; the International Union for Conservation of Nature lists the grey squirrel among the top 100 most harmful invasive species in the world.
Much effort and ingenuity has been expended in halting grey squirrel progress, from trapping (then bludgeoning) and shooting them, to releasing pine martens into their habitats. From 2016 to 2020, Red Squirrels United – a campaign supported by over 30 conservation groups – set out to control their spread (and claims to have now made nine areas in the British Isles safe for reds); even Prince Charles, as patron of the Red Squirrel Survival Trust, has put his weight behind eliminating greys.
The latest move, a workable system for which was thought to be a decade away, is sterilisation. Fertility-based wildlife control is not unusual – though it has been controversial. In northern Italy, a sterilisation campaign for greys was considered 20 years ago as a humane alternative to live capture and euthanasia with halothane. However, legal challenges brought so many delays that the invasive grey squirrel population expanded to an unmanageable level and eradication plans were abandoned. The main issue in Britain was thought to be more technological than legal – designing an oral contraceptive that targets only grey squirrels. But scientists are now testing a special feeder that would distinguish them by body weight. Another possibility in the years ahead is to use DNA editing to ensure grey females are born infertile.
There is an uncomfortable tinge of xenophobia to some of the language used about a species which has now been here for nearly 150 years (and, in many areas, is the only type of squirrel anyone has seen), while it is instructive to note that reds – which also strip bark and take eggs – were seen as pests until the early 1930s, and extensively culled. There is, too, a strong argument that ecosystems change: that that is their essential nature, in fact, and it is quixotic to stop it. Grey squirrels do actively threaten another species in Britain with extinction. The attraction of contraceptive methods is that they are less inhumane, and aim for balance rather than eradication. A willed stalemate, if you will.
