The disappearance of a satellite-tagged hen harrier in "suspicious" circumstances will not halt vital conservation work to protect endangered species, a charity has vowed.

Calluna, a young female harrier, was tagged this summer at a nest on the National Trust for Scotland's (NTS) Mar Lodge estate near Braemar, Aberdeenshire, as part of the charity's EU-funded Hen Harrier LIFE project.

Her last recorded position was on a grouse moor a few miles north of Ballater, in the Cairngorms National Park.

Conservationists have called the unexplained disappearance "very concerning" and are urging anyone with information to contact police.

David Frew, operations manager at the Mar Lodge estate for NTS, said staff at the charity and estate are "deeply saddened" by the apparent loss of the bird.

"She was the result of only the second successful breeding attempt by hen harriers on the estate in living memory," he said.

"We are not going to let this stop our vital conservation work. We are going to carry on at Mar Lodge and our other properties, doing what we can to ensure the survival and recovery of endangered species."

Data from Calluna's transmitter was being monitored by RSPB Scotland and showed that the bird fledged from the nest in July, left the area in early August and gradually headed east over the Deeside moors.

Transmissions were said to have ended "abruptly" on August 12, the start of the grouse shooting season.

Ian Thomson, head of investigations at RSPB Scotland, said: "This bird joins the lengthening list of satellite-tagged birds of prey that have disappeared, in highly suspicious circumstances, almost exclusively in areas intensively managed for grouse shooting."

He went on: "The transmitters used in this project are incredibly reliable and the sudden halt in data being received from it, with no hint of a malfunction, is very concerning"

A Scottish Gamekeepers Association (SGA) spokesman said: "Obviously any news like this is very disappointing.

"The SGA condemns raptor persecution and if any of our members are convicted of a wildlife crime they are removed from our organisation.

"We have learned from those monitoring tags that birds can move some distance away from where they were last recorded so it is important that, if people know anything, they alert the police immediately.''

Hen harriers are one of the UK's rarest raptors and are struggling even in Scotland, their stronghold.

The number of breeding pairs in Scotland now stands at 460, a fall of 27% since 2004, RSPB Scotland said.

The NTS reported that another hen harrier chick it tagged last year, named Harriet, remains alive and well, having overwintered in the Lake District and returned to Mar Lodge estate earlier this year.

The estate is made up of more than 29,000 hectares of moors, Caledonian pine forest, mountains and wetlands and is home to wading birds and otters. It is described as one of the most important areas for nature conservation in Britain.