A golden eagle has been found dead on the Queensberry Estate in Dumfries and Galloway.
A member of the gamekeeping team found the bird on the ground during routine duties.
The police and the South of Scotland Golden Eagle Project (SSGEP) were informed immediately.
It is understood that the bird was an adult, wearing a monitor linked to the SSGEP.
Kirsty Innes, South of Scotland Golden Eagle Project, said: "Whilst it is very sad to learn of the death of one of our eagles, the project still has 38 birds in the region so there is lots of potential.
"The rest of the birds are still flourishing."
Kirsty also confirmed that the dead bird was a female and part of the project.
She added that there were no signs of physical injury and that Police Scotland was now carrying out tests to determine how the bird died.
The tests are wide-ranging and include potential bird flu or poisoning. It's not clear yet when the results will be available.
They are hopeful that the birds which were introduced in 2018 will be settled enough to begin mating this year.
Benny Higgins, executive chairman of Buccleuch said: “Buccleuch work closely with the SSGEP in the local area and we are extremely proud of our record in recent years of helping rebuild the population.
“The bird was removed from the site on Saturday and is being tested to understand the cause of death.
"Our team will continue to offer any assistance it can on this matter.”
The South of Scotland Golden Eagle Project was named Scottish Project of The Year in the 2022 National Lottery Awards.
The project beat off stiff competition from more than 1300 organisations to reach the public voting stage in the National Lottery Awards.
The project emerged as the Scotland winner following the public vote.
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