The hen harrier, one of the country’s rarest birds of prey, could be in danger of disappearing from England, a study has found.

Only six pairs bred successfully this year, a figure described as “critically low”. This has made the hawks especially vulnerable to hunters and natural events.

For years the hen harrier has been at the centre of a dispute between the hunting fraternity — which says the bird destroys their livelihoods by killing grouse chicks — and conservationists who accuse gamekeepers of persecution by illegally killing the harriers.

The figures, released by Natural England and the Royal Society for the Protection of Birds, are the worst since monitoring began in 2002. They are believed to be the result of a harsh winter and a shortage of prey. Last year there were 10 breeding pairs.

Professor John Edwards, chairman of the Hawk and Owl Trust, said the birds were still being targeted by gamekeepers.

“It is likely there is still persecution,” said Edwards. “It’s just barbaric in this day and age.”

The hen harrier used to nest throughout Britain. William Dunbar, the medieval poet, wrote about the “Sanct Martynis fowle”, believed to be the hawk, but by the end of the 19th century it had become extinct in Britain. The population recovered only after the second world war.

There are now hundreds of pairs in Scotland, but the English stock is falling.

Of the six pairs bred this year, four were at the Forest of Bowland in Lancashire. The other pairs were bred at undisclosed locations.

“When a species gets down to as few as half a dozen pairs, then any mortality is likely to be critical,” said Edwards.

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