Can culling non-native species such as the grey squirrel be justified? Only if they pose a ‘credible threat’, according to one ecologist

Grey squirrel culls are a popular – and controversial – method for controlling the UK’s best-known invasive species. Native to North America, the grey cousin of our own native red squirrel was first introduced into British woodlands in the 1870s.

Often believed to be a highly adaptable species that was able to rapidly colonise the UK, the grey squirrel’s widespread distribution is more likely a result of numerous introductions over several decades. According to Lisa Signorile, a biologist at Imperial College London, one of the worst offenders at spreading grey squirrels was the 11th Duke of Bedford, Herbrand Russell, who released and gifted many grey squirrels around the UK.

Grey squirrels are adaptable, however, and outcompete red squirrels for resources. They also carry diseases such as squirrel pox, a virus that is usually fatal to red squirrels, but which greys rarely contract. As a result, grey squirrels have largely displaced reds in their historic habitats across England and Wales, and several conservation charities have decided that a grey squirrel cull is the only solution to preserving the UK’s biodiversity.

However, ecologist Nigel Dudley says that control of non-native species such as the grey squirrel is only justified if they pose a ‘credible threat’ to the existence of other species. In his new book, Why Biodiversity Matters, Dudley highlights that red squirrels are not in danger of extinction on a global basis and still have healthy populations in parts of Britain. This is in contrast with places such as long-isolated islands, where invasive species can and do have a devastating effect on endemic, native ones. As a consequence, he argues, grey squirrel culls are not necessary for protecting biodiversity.

In Why Biodiversity Matters, Dudley goes on to discuss how three important ethical issues – human rights, animal rights and biodiversity rights (which he defines as ‘the right of all species to continue their natural span of existence within a functioning ecosystem’) – interact and sometimes clash. Protecting biodiversity, he says, does not mean prioritising animal lives at all cost, or focusing narrowly on nature’s economic values.

‘It’s not that the ecosystem services are unimportant, far from it,’ says Dudley. ‘But there has been a tendency for the utilitarian and economic values of wild plants and animals to dominate discussion to the exclusion of the basic rights that species have to live their natural evolutionary span.’ Dudley says the failure of some governments to respect biodiversity rights is threatening the survival of many species, as well as the future of the planet.