The manager of the project which saw golden eagles reintroduced to Donegal in 2001 says a bird which was found dead last month had been poisoned.
The bird was found dead in Glenveagh National Park and toxicology tests confirmed it had been poisoned.
Lorcan O'Toole from the Golden Eagle Trust said there were fears that more birds may have been killed in the same manner.
He confirmed that the female bird was found dead on a hillside in the park on Thursday 19 February.
A post mortem and toxicology tests showed the 10-month old bird had died from poisoning and had been dead for about two weeks before she was found.
Mr O'Toole said that apart from the loss of this bird, he believes more birds may have been 'lost to persecution in this area' since 2005 and he referred to a young pair which have not been seen since spring 2006.
'Eagles very rarely die from natural causes at that age,' he said, 'and we now believe that they were also poisoned.'
