RSPB Scotland has said it is "devastated" by the death of a hen harrier found shot and the disappearance of two more birds.
The dead bird was discovered by a member of the public near Wanlockhead, in the south of Scotland, in June.
Two other hen harriers last recorded in northern Scotland have also disappeared in "suspicious circumstances".
Anyone with information has been urged to contact Police Scotland or the RSPB's raptor crime hotline.
What has happened?
The first incident occurred on a grouse moor on the boundary between Dumfries and Galloway and South Lanarkshire on 7 June.
A post mortem examination found the bird died of "penetrating trauma" injuries consistent with shooting - it also showed the bird had been shot before.
The disappeared birds had been tagged as part of an RSPB project this summer.
One of them - which had its tracker fitted after it fledged from a nest on the Mar Lodge Estate in Aberdeenshire - was last recorded on 11 September over a grouse moor between Tomintoul and Grantown-on-Spey.
The final transmission from the other hen harrier - tagged in Easter Ross - came on 12 October in east Sutherland.
RSPB Scotland said that despite laws to protect them, hen harriers remained one of the UK's "rarest and most persecuted birds of prey".
Dr Cathleen Thomas, Hen Harrier LIFE project manager, said: "We're devastated to have lost more young birds in suspicious circumstances."
Scottish Land & Estates (SLE) said the incidents were a matter of concern but described the RSPB's appeal as a "blatant attempt" to put pressure on the government ahead of the publication of a report into grouse moor management.
A group looking at the issue - chaired by Prof Alan Werritty - delivered its findings to the Scottish government last month.
The SLE said that there were "serious questions" about the reliability of tags and not every failure meant a crime had been committed.
It also said the incident at Wanlockhead had been investigated by police and the estate where the dead bird had been found had hosted "several successful hen harrier nests".
The Scottish Gamekeepers Association said it had an "unequivocal stance" on wildlife crime and had removed eight members in the last seven years.
It echoed claims RSPB Scotland was trying to put pressure on the Scottish government.
A report issued earlier this year looked at the "successes and challenges" of moorland management on land in southern Scotland.
The Langholm Moor Demonstration Project aimed to see if a grouse moor could be commercially viable while at the same time protecting hen harriers and other raptors.
Some elements of it were deemed to be a success including addressing decades of heather loss.
However, grouse numbers did not recover sufficiently for commercial shooting.