Hen harrier breeding season 'very poor' says RSPB
It is set to be a "very poor" year for hen harriers, with only a handful of nest attempts so far, the RSPB said.
The "persecuted" birds are the focus of a government plan to increase their numbers across moorlands in England.
The charity said "human interference" could be a factor for the lack of nests and cited a recent incident involving an armed man in the Peak District.
Raptor Persecution UK, a conservation group, said the plan was not working and the RSPB should withdraw support.
The action plan, launched in January by the Department for Environment, Food and Rural Affairs (Defra) and supported by organisations including the RSPB and the Moorland Association, was set up to revive the bird's fortunes.
It followed the disappearance of five male hen harriers from sites in Lancashire and Cumbria, in 2015, leading to the collapse of nests.
The hen harriers' predation of grouse has been a source of conflict on moors used for shooting, but there was hope the diverse partners could come together and reverse the decline.
However, several incidents have led some conservation groups to suggest that little has changed.
In April, a video emerged apparently showing an armed man using a decoy bird to attract a hen harrier in the Derbyshire Peak District.
In May, a man was caught on camera setting illegal pole traps on the Mossdale estate, near Hawes, North Yorkshire.
In both incidents hen harriers had been spotted in the area.
A spokeswoman for Raptor Persecution UK said: "There has been clear evidence that illegal raptor persecution is continuing.
"The RSPB should withdraw its support of the Hen Harrier Action Plan and join the increasing call for a ban on driven grouse shooting."
Martin Harper, the RSPB's conservation director, said it was too "premature to change tack" and hoped by the end of the season there might be progress.
Amanda Anderson, director of the Moorland Association, which supports grouse shooting, said the organisation was committed to the successful breeding of hen harriers.
"We have joined voices with conservationists to condemn all wildlife crime and will continue to do so," she said.