In short:

The combined impact of bird flu and a proposed wind farm in Victoria's south-west poses risks to threatened bird and bat species, ecologists say.

Developer HMC Capital says the project has undertaken extensive measures to mitigate the risks.

What's next?

A decision is expected on the future of the Kentbruck wind farm next month.

Expertly camouflaged amid reed beds and sedgeland, the elusive Australasian bittern is a highly revered sight among birdwatchers.

Across Australia, fewer than 1,500 birds are estimated to remain in the wild.

In south-west Victoria, a small population of the endangered birds inhabit the Glenelg Estuary and Discovery Bay Wetlands all year round.

In winter, the population at the Ramsar-listed site grows when more birds fly hundreds of kilometres south after breeding on the inland rice fields of the New South Wales Riverina.

The bittern, along with the endangered fairy tern, hooded plover and the brolga, which is also at risk from habitat loss in Victoria, are among the species ecologist and managing director of the Nature Glenelg Trust Mark Bachmann holds concerns for amid nearby mass bird flu mortality events and a proposed 105-turbine wind farm.

"The big question … we just don't know which species are most likely to be severely impacted by bird flu,"he said.

In August, hundreds of dead and dying birds were found to have contracted H5N1 avian influenza at Portland and the Glenelg River Estuary at Nelson.

Mr Bachmann said the "compounding threat" associated with bird flu "presents too much risk for the wind farm project to go ahead".

Decision on nation's tallest turbines looms

Seven years ago, renewable energy developer HMC Capital put forward plans for the wind farm — including turbines up to 270 metres tall — in commercial pine plantation land between Nelson and Portland.

A final decision on the 600-megawatt Kentbruck Green Power Hub project is expected on November 10.

A spokesperson for the developer said the project's approach was "highly sensitive to the impact on birds" and had undertaken "extensive research" and independent expert investigations to mitigate the risk to birdlife and bat species inhabiting the nearby wetlands.

Among measures taken to placate dissent from community members and environment groups, the developer reduced the number of wind turbines by 33 per cent and agreed to set up a $30 million ecology fund to sponsor ecological studies, protection activities and species recovery projects.

The spokesperson added that the wind farm project was "critical for the transition to clean energy and will power hundreds of thousands of homes, as well as provide power to the nearby Port of Portland and Portland Aluminium Smelter".

A 'litmus test' for renewables projects

Back in Nelson, Mr Bachmann said the federal government's looming decision on the wind farm would be "critical" to the intersection of environment, community and future renewables development.

The project, he said, would see turbines situated about 300 metres from the Ramsar wetland and 500 metres from the coast, "potentially disrupting flight paths of birds and bats".

"This is the dilemma of developments like this being placed in close proximity to really biodiverse areas; you just encounter lots and lots of these issues."

Mr Bachmann argued the additional proximity to coastal areas experiencing "more frequent" bird flu cases heightened uncertainty.

He said the impending decision on the wind farm would set a national precedent.

"It could either deter development in inappropriate locations, or it could signal that you can pretty much put a wind farm anywhere.

"There's a lot at stake here."