Continued illegal persecution of hen harriers is pushing the bird of prey to the brink of extinction in England, says the Government's conservation body.
A report by Natural England said hen harriers were particularly at risk from systematic persecution and disruption in areas managed for red grouse or gamebird rearing.
As a result, there are critically low numbers of breeding pairs on areas which provide suitable habitat and could support healthy populations.
Natural England chairman Sir Martin Doughty said today the hen harrier had become the "emblem of man's callous disregard" for the country's wildlife.
Only a quarter (26 per cent) of breeding pairs on red grouse moors manage to produce fledged chicks, while Natural England said there was "compelling evidence" that persecution continued at communal winter roosts.
In one 12-month period, six birds fitted with satellite transmitters were tracked from the hen harrier stronghold of Bowland Fells into parts of the North Pennines managed as driven grouse moors – and literally disappeared off the map.
They have not been recorded subsequently, while in another incident three signals "went dead" in one geographical area between 2007 and 2008.
Monitoring work since 2002 revealed that the relatively tiny area at Bowland, Lancashire, was the site of more than two-thirds of the 127 breeding attempts by the once-common hen harriers during that time.
Bowland, where Natural England and the RSPB work with private landowners and gamekeepers to manage the area in a way that supports the birds, is the only place in England where the bird has increased since the hen harrier recovery project started in 2002.
Some 50 of the 72 successful nesting attempts – in which hen harrier chicks fledged – in the past seven years were at Bowland.
A report in September showed there were just a handful of successful nests again this year, despite estimates by the RSPB that the country's uplands could support at least 200 breeding pairs.
The monitoring programme by the RSPB and Natural England found there were just 10 nests where the chicks were successfully reared, out of 19 attempts.
Last year the figure was 14 successes from 23 attempts, and the number of successful nests in England has not exceeded 15 in any year since 1994.
The hen harrier became extinct in the UK in Victorian times and recolonised in Scotland – where there are now 630 breeding pairs – in the interwar years.
They only began to come back in England in the 1970s and numbers remain extremely low.
Sir Martin said: "This magnificent bird is being persecuted to the brink of extinction as a breeding species in England."
Mark Avery, RSPB director of conservation, said: "The findings of this report reinforce what the RSPB has been saying for years: the hen harrier is being driven to extinction in England by illegal killing."