The scientist in charge of the reintroduction of white-tailed sea eagles into this country said the loss of two birds, a male and female, over the past days was "a huge blow" to the project.
The birds, 15 of which were brought from Norway to the Killarney National Park last June, are protected under the Wildlife Acts. The National Parks and Wildlife Service and gardaí are investigating. The eagles had been absent from Ireland for 100 years.
Minister for the Environment John Gormley has expressed his disappointment. A statement from his department said it was "a terrible loss".
The two juvenile eagles were found dead within hours and within metres of each other in the Glencar area of the MacGillycuddy's Reeks on the Iveragh peninsula on Monday evening and yesterday morning. They were outside the national park and in hill sheep-farming country.
They had apparently been poisoned, although perhaps not deliberately, as the poison may have been laid indiscriminately to target foxes and grey crows in advance of the lambing season. In cold weather, some poisons are more effective, however the use of poisoned meat bait is banned since early this year.
The birds were otherwise very healthy according to Dr Allan Mee, the project co-ordinator.
A full analysis will be done at the regional veterinary laboratory in Cork where Dr Mee and wildlife rangers brought them last night.
Most farmers in the area were supportive of the ambitious project and one farmer who had seen the large dead male on Monday night was very upset, Dr Mee said.
A sheep carcass found some kilometres away from the eagles has been sent for toxicology analysis.
Dr Mee, who works closely with farm groups, said: "Our biggest hurdle is education. The vast majority of farmers are well-disposed. We need to make farmers aware that when they put out poison, scavenger birds, along with target species such as foxes, will die."
The sea eagle is among the world's largest birds of prey. Kept in specially built cages and with minimal contact with humans, they had been introduced into the wilds in the Killarney National Park from August. Apart from one death in November near the release area of Tomies Mountain, they had been doing well.
Threats and warnings by concerned farmers who feared for their lambs had not materialised, amid overwhelming public support for the birds. However, these deaths ahead of the lambing season is leading to some concern.
Soaring thousands of feet and spreading as far west as the Blasket Island and the Skellig Rock, several birds have stayed around Killarney, particularly near the Eagles' Nest area of the Lakes of Killarney where their dramatic appearance has already become a focal point for visitors. The project receives an annual grant of €10,000 from the town council and is supported by hotels and tourism bodies.
Lorcán O'Toole, manager of the Golden Eagle Trust in Donegal and partner in the white-tailed project, said it was "a big disappointment", but the project remained on track.
There are now five females left in the Killarney group. It is hoped they will breed in the next four to five years and that further reintroductions will continue.