A satellite tag fitted to a hen harrier has stopped transmitting in the same mountains where eight tagged eagles "vanished", RSPB Scotland has said.
The hen harrier fledged at a nest in Aberdeenshire in July.
The RSPB said its tag last sent information on 3 August from moorland in the Monadhliath Mountains managed for grouse shooting.
The Scottish Gamekeepers Association said there was "no independent information" on the situation.
Last week, RSPB Scotland and the Scottish Moorland Group, whose members include landowners and gamekeepers, clashed over the loss of the eight golden eagles between 2011 and July this year.
The wildlife charity believes they were killed illegally around grouse moors, and their satellite tracking tags destroyed.
The Scottish Moorland Group said it condemned wildlife crime. It added that the RSPB had not considered other reasons for the loss of the tags.
The hen harrier, known as Elwood, was being monitored under a scheme run by the Partnership for Action against Wildlife Crime Scotland.
After fledging at a nest site in Aberdeenshire the bird spent time near Tomatin, south of Inverness.
The bird's tag last transmitted information a few miles from the Slochd Summit on the A9.
Ian Thomson, RSPB Scotland's head of investigations, said: "This latest disappearance of a satellite tagged bird is deeply concerning, and joins the long list of protected birds of prey that have been confirmed to have been illegally killed or disappeared suddenly in this area.
"The transmitters being fitted to these birds are exceedingly reliable, and illegal persecution is therefore the most likely explanation of the disappearance of these birds of prey.
"The absence of typical breeding raptor species from areas of suitable habitat, or at traditional nesting sites, in large parts of the Monadhliaths is further supporting evidence of a major problem with wildlife crime in this general area."
A spokesman for SGA said: "As with other recent allegations, the SGA will work with Police Scotland and Scottish government in an attempt to get to the bottom of this. It is clearly a situation which cannot go on.
"We have no independent information, at the present time, so getting the facts will be the first step. Speculation, at this stage, will not help.
"The SGA does not, and will never, condone wildlife crime. As an organisation we advocate legal solutions, solely, as the means to resolve conflicts. If there is any evidence of illegal activity by an SGA member, appropriate action will be taken."
Tim Baynes, director of the Scottish Moorland Group, added: "We are as concerned as anyone when a satellite tagged bird goes missing and particularly in this case because the bird was part of a project involving Scottish Land and Estates and our members.
"This bird was tagged on one of our member estates as part of the Heads Up For Harriers."
He added: "Estates in the area where the bird went missing are also concerned but have not been approached by RSPB to help in any search. They are unaware of any incident and would be willing to help."
- 11 August 2016