A bird no larger than a cricket ball could derail plans to build the biggest coal mine in Australia.
A legal challenge to Indian giant Adani's plans for the $16.5 billion Carmichael mine by environment group Coast and Country began in the Land Court of Queensland on Tuesday.
If approved, the project would extract at least 50 million tonnes of coal a year from the Galilee Basin and export it through the Abbot Point coal terminal, north of Bowen.
"The environmental harm it will cause, or is at risk of causing, will be correspondingly great," lawyer Saul Holt QC, for Coast and Country, told the court.
The case will put the spotlight on environmental and economic concerns, including the plight of the endangered Black-Throated Finch.
"If this mine goes ahead ... there is a high likelihood of species-threatening harm to the world's most significant population of the endangered Black-Throated Finch," Mr Holt said.
"As an environmental issue and risk, it is of the first order and it will be treated as such."
The mine would also have an effect on the threatened Waxy Cabbage Palm and may dry up the nearby Doongmabulla Springs, opponents argue.
But lawyer Peter Ambrose, for Adani, defended the company's environmental modelling and previewed evidence by a range of experts in his opening address.
The company accepts there has been a serious decline in finch populations - which Mr Holt said was 80 per cent since the 1980s.
But Adani pointed to offset and management plans that would "provide appropriate controls on the environmental impact".
In exchange for the 9789 hectares of habitat that would be affected by the mine, there was an offset area of 30,999ha, Mr Ambrose said.
"The applicant's evidence is they don't have to move too far, as the offset areas are right beside where they are known to breed."
Mr Ambrose cited estimates the mine could produce net economic benefits of between $18.6 billion and $22.8 billion.
But Mr Holt said the project would also contribute to the degradation of the Great Barrier Reef through a contribution to climate change.
Adani's witnesses will argue that thermal coal use is generated by demand - not supply - and electricity generators would find alternative sources of coal if the mine does not go ahead.
Therefore, Adani argues, there will be no net increase in greenhouse gas emissions.