The RSPB has called for sporting estates to stamp out illegal persecution of the protected hen harrier after a male bird was allegedly hunted down and shot in the Cairngorms.
But gamekeepers say they should not be “demonised”.
Conservationists described the killing, on a Highlands grouse moor, as “appalling”. Two witnesses reported the incident to police on 30 May last year.
They described watching for almost three hours as two people with shotguns searched the moor for the bird’s perch. It’s believed the gunmen were taking directions by radio from at least one other person in a vehicle.
A police investigation was launched but found insufficient evidence to bring charges.
Ian Thomson, RSPB Scotland’s head of investigations, said: “All the evidence indicates that this appears to have been an appalling, organised killing of one of our rarest birds of prey, which shows a complete disregard of the laws protecting our wildlife. The hen harrier population in Scotland is in trouble, with a 20 per cent decline from 2004 to 2010.
“The intolerance shown towards this species on grouse moors, with this latest case being yet another example, gives a clear indication of one of the main causes of this decline.”
The harrier is a natural predator of the red grouse but the conservation charity said techniques such as providing alternative food have proven effective and should be more widely embraced.
But a spokesman from the Scottish Gamekeepers Association said: “Our understanding from the case in the Cairngorms is that there is no evidence to support the RSPB’s interpretation of events, and the RSPB is aware of this.
“The RSPB, as a bird charity, could spend donor money more wisely by assessing the bigger picture of harrier decline and the criminal drop in the smaller, less-iconic prey birds, rather than spending it on demonising gamekeepers.”
The spokesman argued that the vast majority of land managers work within the law in challenging circumstances to ensure a balance of species is maintained alongside grouse for sport.
Last year the Partnership Against Wildlife Crime Scotland launched its Heads up for Harriers project, aiming to raise public awareness of the bird’s plight and prevent illegal persecution.
Duncan Orr-Ewing, RSPB Scotland’s head of species and land management, said gamekeepers should protect grouse chicks by providing alternative food sources for the raptors.
He said diversionary feeding – putting out food such as chicks and rats for hen harriers – is proven to cut the numbers of grouse chicks taken for food by up to 86 per cent.
The SGA insisted it advocates legal methods for dealing with species conflicts.
The hen harrier is on the red list of endangered species with fewer than 500 breeding pairs in Scotland.
In England, the species is on the verge of extinction.