A common farm chemical possibly made into baits is believed to be behind the mass deaths of protected sulphur-crested cockatoos in Tatong, near Benalla.
More than 250 of the birds died in January and February, prompting calls to wildlife officers from the Department of Environment, Land, Water and Planning.
DELWP senior forests investigator Greg Chant said testing of samples from the dead birds indicated they had died from omethoate poisoning.
‘‘Omethoate is a common farm chemical used to protect crops from red-legged earth mites,’’ he said.
‘‘It’s possible omethoate was illegally used to create a homemade bait, which the birds ate.’’
The cockatoos are protected under the Wildlife Act and there are significant penalties, including imprisonment, for hunting, taking or destroying protected species.
It is also illegal to make bait products without appropriate authorisation, Mr Chant said.
‘‘The incident highlights that using chemical products in an illegal way poses an unacceptable risk to wildlife,’’ he said.
‘‘It is unclear if the birds were deliberately poisoned or not, but illegally destroying protected native wildlife is a serious environmental crime.’’
The department is looking for the person responsible and anyone with information can make anonymous calls to the department on 136186 or Crime Stoppers on 1800300000.