Four rare birds of prey have been killed by “deliberate” poisoning, the RSPCA said.
The four goshawks and a buzzard were discovered in woodland to the west of Exeter, Devon.
The charity said there were only 20 breeding goshawk pairs left in the county. It is now offering a £1,000 reward for information leading to a conviction.
The birds were killed with the banned pesticide carbofuran. This substance has been identified in a number of other bird of prey poisoning incidents, the RSPB said.
All birds of prey are fully protected under the Wildlife and Countryside Act 1981, but goshawks are specially protected because of their low numbers.
There are believed to be only 410 pairs of nesting goshawks in the whole of the UK.
Devon and Cornwall Police have joined forces with the RSPB to investigate the incident and are appealing for information.
PC Josh Marshall, wildlife crime officer with Devon and Cornwall police, said: “These four goshawks represent a significant percentage of the Devon population and it’s a huge setback for what is a magnificent bird.”
The RSPB was informed of the incident by a member of the public in March and recovered the birds in liaison with the police and the Forestry Commission, which owns the land.
Only now have toxicology reports revealed that the birds were poisoned.
Forestry Commission ranger for the area Ian Parsons said: “The people that do this to our wildlife not only deprive people of the chance to see these rare birds but they also put the public at risk.
“The poison involved is lethal to dogs and humans and the land where this happened is open to the public. These people obviously don’t care about the dangers of doing this.”
Members of the public with any information are being urged to contact the police or call Crimestoppers on 0800 555 111.