RARE Eagle Owls are believed to be ruining efforts to build up the population of hen harriers in the Ribble Valley.

The large birds of prey, which are brown and black, can grow to over two feet tall and have a wing span of over a metre, began nesting at Dunsop Bridge in the Trough of Bowland earlier this year.

A footpath, off Whitendale Road was shut in May following the discovery of the birds, which began swooping on walkers and which are believed to have escaped from captivity.

But wildlife police have so far discovered the remains of three hen harriers near the nesting site.

Stuart Burgess, senior press officer for Natural England which runs a harrier recovery programme said: "Natural England is concerned about the perilously low population of hen harriers in England. Our Hen Harrier Recovery Project is working to have a sustainable population of hen harriers that would not be threatened by predation. Eagle owls can breed well in captivity and we would ask that people do not release them and make sure they do not escape and this may actually be illegal."

Eagle owls are not native to the UK but are very common in Scandinavia, Southern Europe, Eastern Europe and Asia.

They will eat almost anything that moves - from beetles to roe deer fawns.

Lancashire police Wildlife officer PC Duncan Thomas said: "Lancashire police and key partners have been monitoring the eagle owl site at Dunsop closely during the breeding season. The adults have successfully fledged three young, which are currently dispersing through the valley. As part of this monitoring process and at the request of local land managers, we have made a number of searches of the rearing site to collate the amounts and types of species the owls have preyed on.

"During the last search we located the remains of a female hen harrier and the suspected remains of a male hen harrier. The site was further visited and the remains recovered. During this visit further remains were located to indicate possible predation on a juvenile hen harrier. They have been submitted for analysis and all available information clearly indicates natural predation."

A spokesman for the National Gamekeepers' Organisation (NGO) said: "Gamekeepers have been warning for some time about how the profileration of eagle owls and this incident confirms just how predatory they can be. It should also serve to remind those who routinely criticise gamekeepers for killing these birds to protect the grouse population that hen harriers can actually die from natural causes.

"The NGO has recently criticised the Government over its inadequate policy for dealing with non-native species, and this incident emphasises the point. Some keepers may well be tempted to say 'every cloud has a silver lining' but what we really need is a proper legal framework for managing grouse, hen harriers and non-native species."

Tim Melling, a conservation officer for the Royal Society for the Protection of Birds, said: "There is no evidence that they have occurred naturally in England since it was an island and connected to the continent via a land bridge.

"However, they are common escapees and there is probably not a town in the country that doesn't have a set of these birds."