Should wild animals be reintroduced into areas where they have become extinct? In recent years, the issue has split European conservationists and farmers, who disagree over the future of species such as wolves. Now the unexpected arrival of a tiny population of owls in Britain has divided even advocates of conservation.

The breeding pair of eagle owls (Bubo bubo) first attracted attention last autumn, when they featured in a television documentary. Many ornithologists believe that the birds, which have a wingspan of two metres, haven't lived in Britain since the last ice age, 10,000 years ago. The owls are fearsome hunters, happy to dine on mammals — sometimes as large as small deer — or on other birds of prey.

The Royal Society for the Protection of Birds is calling on the British government to monitor the new arrivals, resident in Yorkshire in northern England, in case the population grows. The society is worried that the owls might start to kill significant numbers of endangered species, such as black grouse and hen harriers.

It’s churlish to suggest that the owls don’t belong here.

But some researchers argue that eagle owls should be protected as native birds. John Stewart, a palaeontologist at University College London, says fossil evidence suggests that the owls survived previous ice ages. He argues that remains from the past 10,000 years should be taken as evidence that the owls existed in the wild — ornithologists had previously assumed that the remains came from tame eagle owls that had been imported for hunting. “If you look at the owls' distribution around Europe, it is like that of other animals such as wolves and beavers that have been pushed out of northwest Europe,” adds Stewart. “It's churlish to suggest that they don't belong here.”

If he is right, eagle owls could be added to the British List, the register of birds recorded in recent times in Britain and Ireland. This would give them the right to be protected, and perhaps even actively reintroduced. But Tim Melling, secretary of the records committee at the British Ornithologists' Union, which compiles the list, says he is not convinced by Stewart's points.

Melling says he and colleagues have reviewed every published British bird book and found no evidence for an established population of eagle owls. He points out that the birds have been popular pets for hundreds of years and that reports of wild eagle owls often note that the animals are unusually tame.

A similar debate over belonging was ignited last year by carbon dating of bones of the Eurasian lynx (Lynx lynx) from caves in Yorkshire. The lynx was thought to have died out in Britain several thousand years ago, when climate change turned much of its forest habitat into boggy peatlands. But the bones were just 1,500 years old, suggesting that recent human activity was responsible for the animals' demise.

The result was a boost for conservationists wanting to bring the lynx back to Britain, including David Hetherington, who led the carbon-dating study at the University of Aberdeen. He suggests that forestry projects and deer in the Scottish Highlands would provide suitable habitat and prey.

But whatever the fossil evidence, any reintroduction needs local backing, cautions Toby Aykroyd, vice-chairman of the Wilderness Foundation, a charity based in Chelmsford, Essex. Farmers in France have protested against the return of wolves, which prey on livestock. And beavers, which have been successfully reintroduced in many European countries, have proved controversial in Britain: farmers fear they will be not be allowed to remove the animals from their land.

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Soar point: should the eagle owl be allowed to repopulate Britain?