THE National Parks and Wildlife Service (NPWS) is investigating the deaths of nine magpies found near Hyde Street, South Grafton, last week.
NPWS Clarence Area manager Andrew Lugg said there was no visible signs of death.
"Although there may be a natural explanation, we cannot rule out the possibility that the birds have been deliberately or accidentally poisoned," he said.
Mr Lugg said magpies were a protected species, and anyone found to have deliberately harmed them would face heavy penalties.
He asked for anyone with information to contact the NPWS in Grafton.