The Victorian Conservation Regulator is investigating the death of more than 100 little corellas in the state's north-west.
Bohollow Wildlife Shelter's Kirsty Ramadan was called out to the Barmah area to collect what she thought would be a few sick birds.
Instead she collected 106 bodies.
"I quickly realised once I started scouting out around the town there were dozens upon dozens of dead or dying birds in the bushland and on the riverbanks" Ms Ramadan said.
One bird was found alive but died later that night and another was taken to a veterinarian in Echuca.
"We opened up the bird and inside it had haemorrhaged along the entire intestine." Ms Ramadan said.
"We opened up the gizzard to get a sample of what they consumed and inside was a green stain, which is indicative of rodent poisons."
Probe underway
The Conservation Regulator is working to determine whether the deaths were caused by a disease or because of human actions.
The Department of Environment, Land, Water and Planning acknowledged that native birds could be attracted to poisoned grain intended to kill rodents.
Killing wildlife by poison is an offence under the Wildlife Act 1975 and a person found guilty can receive penalties of up to $18,174 and/or six months in prison.
Authorities do not want to rule out the possibility of disease, such as psittacine beak and feather disease, which has caused native bird deaths in Victoria.
A spokesperson for the Conservation Regulator says anyone with information about this incident or cases of wildlife crime is urged to contact Crime Stoppers Victoria on 1800 333 000.
'One of the worst'
Ms Ramadan has been working in wildlife rescue around the area for more than 30 years and says this is not the first time she has seen mass bird deaths.
"Hotspots for this occurring are Numurkah, Nathalia, Barmah and over towards Kyabram way," she said.
"This is probably one of the worst incidents, however another one similar to this magnitude happened in Nathalia, which is not far from Barmah."
Ms Ramadan urged people to stop using poison for baiting because it could lead to secondary poisoning of raptors and other native wildlife.
"It's just horrific to see such a waste of life," she said.
"With our human activities encroaching more on their natural habitat, we need to learn to live with them rather than just do away with them as soon as they become an inconvenience."
