Two endangered hen harriers have died with one believed to have starved to death and the other left weak after flying hundreds of miles.
Sibling chicks, Grayse and Mannin, were fitted with satellite trackers on the Isle of Man for a protection programme.
The female bird of prey was found dead on the island last month and the male was washed up on a beach in Scotland.
Manx Birdlife said there were "no signs of stress" and more research was needed to "ensure their survival".
After being tagged, the Manx-born birds were monitored by scientists who sounded the alarm when Grayse's tag became stationary.
Neil Morris, from Manx Birdlife, said: "We formed a search party and found her in a ditch - there was no sign of poisoning or trauma, we think she died of hunger.
"We think Mannin was not strong enough for the journey to Scotland."
Official figures from the Royal Society for the Protection of Birds (RSPB) show a decline in the number of nesting hen harriers.
They are the most endangered breeding bird of prey in England with illegal killings and destruction of their habitat being behind the collapse of their population.
Mr Morris said: "We need to find out more about these birds to ensure their survival.
"The stakes are high, the success of hen harriers on the Isle of Man could prevent extinction."