A man has been arrested after five red kites were found dead in a field.
The birds of prey were found poisoned in Orsett, Thurrock, and a man from Aveley has been arrested.
PC Luke Jones, of Essex Police, said: “Tests have shown that they were poisoned. The poisons used are deadly not only to wildlife but also to humans.”
The force said the man had been released under investigation and its inquiries were continuing.
“Red kites, along with all birds of prey, are protected under the Wildlife and Countryside Act 1981,” said PC Jones.
“Anyone who finds a dead bird of prey or suspects illegal activity should report the information to police via our website. But please take care not to touch them.”
Red kites are found only in Europe and were extinct in England and Scotland 40 years ago.
After hard work from conservationists, their population surged between 1995 and 2022, and there are thought to be 6,000 mating pairs.