A white-tailed eagle which was found dead in a nest in Connemara on 1 April was poisoned, toxicology reports show.
The female eagle was released in Killarney National Park in 2009 as part of a reintroduction programme managed by the Golden Eagle Trust and the National Parks and Wildlife Service.
The bird settled in the Roundstone area of Co Galway, where she paired up with a male.
The pair laid eggs at a nest last year but the eggs failed to hatch successfully.
A post-mortem examination showed the bird was within days of laying another two eggs.
It is the 13th confirmed poisoning of a white-tailed eagle since the reintroduction programme began in 2007.
Of the 100 eagles released, 31 have been found dead.
It is now believed there are 14 breeding pairs in the wild.