A department spokeswoman said the birds died from suspected homemade mouse bait. She said all the birds had been collected for testing.

“The Department of Environment, Land, Water and Planning will continue to investigate the cause of the birds’ death and we hope to know more by the end of the week,” she said.

Department of Environment, Land, Water and Planning wildlife officer Glenn Smith said it was an offence under the Wildlife Act to destroy or interfere with protected wildlife.

“This includes our native bird species, severe penalties apply,” he said.

“We’re working closely with Agriculture Victoria on this issue, but people need to do the right thing.” 

This year’s high mouse populations have continued to deplete sources of rodent bait throughout western Victoria.

Agriculture Victoria chemical standards officer Alex Perera said people, livestock, pets and wildlife were at risk when mouse baits were manufactured illegally. 

“The temptation to make your own bait can be great, but this is risky and dangerous for you and the environment," he said.

"It can lead to the accidental poisoning of pets, working dogs and native animals. 

“By using a registered chemical and following the label people can be assured they are minimising any risks.”

Registered products for mouse control have been through a rigorous assessment by scientists at the Australian Pesticides and Veterinary Medicines Authority.

Mr Perera said the product labels would often contain specific directions on how to prevent off-target poisonings.

“There are also significant penalties associated with the illegal use of agricultural chemicals,” he said.

Mr Smith said people could call 136 186 for more information.