The Royal Society for the Protection of Birds (RSPB) said the female hen harrier was found on its reserve at Geltsdale in Northumberland. It had been poisoned with a banned insecticide called mevinphos.

Two ravens were also found dead

Bait laced with the same poison was also found near two hen harrier nests on the site.

The adult hen harriers from those nests were missing and the fear is that more than one bird may have been killed.

There are fewer than a dozen breeding pairs in England.

'An outrage'

RSPB north England regional manager, Andy Bunten, expressed his horror at the find.

"The loss of these birds to poisoning is an outrage," he said.

"The use of poison in the countryside in this way is illegal, indiscriminate and unnecessary."

Elswhere at the site, two ravens have been found dead. They had been poisoned by carbofuran.

Wardens are trying to provide extra protection to the remaining hen harriers at Geltsdale.

A special government hotline has been set up for the public to report any suspected cases of bird poisoning. The number is: 0800 321600.