About 200 pheasants have been found dead on a Norfolk estate after being poisoned.
The birds had been poisoned with a pesticide
Police believe large amounts of a pesticide containing the toxic chemical aldicarb were put into water systems in the birds' pens on the Ringland Estates, near Norwich.
Department for Environment, Food and Rural Affairs (Defra) scientists are helping police with their investigation.
Experts are carrying out tests on samples taken from the birds' water supplies and from the dead birds.
Dr Ed Blane, Defra's wildlife adviser for Norfolk, said: "The deliberate use of pesticides to poison wildlife is a serious problem.
"But this incident is unusual in that water was poisoned and that the target was gamebirds.
"Typically incidents involve the use of poisoned meat or egg baits laced with
pesticides used to illegally kill predatory animals such as foxes.
'Very concentrated poisons'
"This sort of indiscriminate use exposes a wide range of animals, including pets, to the risk of being poisoned and creates a hazard for humans visiting the area."
He added: "If people see something that looks like a victim of poisoning, or
a poisoned bait, they should report it to Defra straight away.
"Covering it can reduce the risk to other animals, but they shouldn't touch it as the poisonous use substances that are very concentrated poisons."
People who suspect a poisoning incident can report it by calling the free
Wildlife Incident Investigation Scheme hotline on 0800 321600.