Sally was one of only four breeding pairs of Montagu’s harriers in Britain Credit:RSPB Montagu’s harriers are the UK’s rarest breeding bird of prey. For that reason nest sites are kept secret, and fenced off by the RSPB which has been protecting the birds since 1982.But wildlife experts say they are often targeted by landowners and gamekeepers on grouse moors to stop them taking chicks.Sally’s ‘disappearance’ comes almost three years to the day when another tagged Montagu’s harrier called Mo vanished in the same area on land bordering the Sandringham Estate.Sally had the letters ‘CP’ attached to her leg, in honour of the naturalist Chris Packham. Anyone with any information is urged to call Norfolk Police on 101 quoting ref 12815082017. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. Mark Thomas, Montagu’s harrier species lead for the RSPB said: “Since then we have had no more transmissions and she hasn’t been seen despite searching. Roger has been at the nest site, alone.“We are obviously very concerned about what has happened to Sally. This is a major blow for this species in the UK and we are gutted. Norfolk Police have been informed. “Sally, you were a remarkable harrier and have given us a clear insight into the ecology and problems faced by this species.” A rare Montagu’s harrier, which was tagged and released into the wild on BBC Autumnwatch is feared to have been illegally killed.Sally, who was described as the ‘poster girl’ for harrier conservation was released by presenter Martin Hughes-Games last July and has been followed ever since as she migrated to Africa and back to the UK.Along with her mate Roger, another satellite-ragged male, they were one of only four pairs left in Britain, but had been successfully breeding for the last two seasons, raising five young in Norfolk.However the RSPB lost track of Sally on August 6 and there has been no data on her location since. Usually if animals die naturally the tags still operate and their bodies can be found.