Tim Mackrill from the Roy Dennis Wildlife Foundation said: “So many people in the area had shared the joy of seeing these birds breed again after hundreds of years and our ongoing monitoring has shown how well they were fitting into the landscape.
“To have that destroyed just a few months later is deeply shocking.”
Dyfed Powys Police is investigating a similar incident on 13 September, where a satellite tag belonging to white-tailed eagle G615 was recovered in remote moorland near the Gwgia Reservoir, Tregynon.
Police Scotland is treating the disappearance of a third bird as suspicious. The tag for G819 stopped transmitting data daily on 8 November in the Moorfoot Hills area.
The Birds of Poole Harbour group said any illegal persecution of the birds was “sickening”.
The group promotes conservation efforts on the Dorset coast where a single male white-tailed eagle chick hatched earlier this year.
In a Facebook post it said: “The return and recolonisation of white-tailed eagles is still in it’s infancy, so the illegal killing of the birds can have a massive detrimental impact on the project and their recovery across their historic range.”