Avian botulism has been confirmed as the cause of a mass bird death event at Bells Swamp Nature Reserve, south-west of Bendigo.

More than 700 birds have died during the event, which was first reported on 8 February.

Laboratory test results, in combination with the signs observed in affected birds, are consistent with Clostridium botulinum toxin, which attacks the brain and nervous system of infected animals, causing paralysis.

Parks Victoria has coordinated the response as land manager for Bells Swamp, leading a combined effort with the Department of Energy, Environment and Climate Action and other organisations.

Rangers and volunteers have removed dead birds for disposal and collected sick or injured birds for monitoring and care. These efforts will continue over the coming days.

The reserve will remain closed until further notice, to limit disturbance to the birds and protect the public.

Avian botulism is a serious illness of birds caused by a toxin produced by Clostridium botulinum bacteria, which survives as spores in soils and sediment in wetlands and lakes. Events like this one have been recorded in Victoria since 1938, and usually occur in the summer months.

Humans and pets are primarily at risk only if they eat infected fish, birds or maggots, and botulism toxin is not infectious.

More information on avian botulism is available on the Agriculture Victoria website.

Further updates will be posted as Change of Conditions on the Bells Swamp Nature Reserve page on this website.

Quotes attributable to Parks Victoria District Manager Suzanne Hughes

“Since the start of this event we have suspected avian botulism as the cause and that’s now been confirmed. Sadly, hundreds of birds have died but at this stage the event appears to be limited to Bells Swamp.”

"We know the community will be concerned about the event, but avian botulism poses very little risk to humans or pets. We ask that people stay away from Bells Swamp until it is reopened to the public.”

“The efforts of volunteers, Parks Victoria rangers and other agency staff to respond to the event have been magnificent and are deeply appreciated.”