Murray-Darling water targets bring boom time for waterbirds in the Gayini wetlands

Tens of thousands of breeding waterbirds, including the endangered Australasian bittern, are thriving in the culturally important Gayini (Nimmie-Caira) wetlands in south-west NSW.

The event is the result of a collaborative effort involving UNSW Centre for Ecosystem Science and Charles Sturt researchers, state and federal environmental water managers, and traditional owners.

Researchers say this has been one of the largest colonial waterbird breeding events this year, supported solely by water that has been specifically set aside for the environment.

“This has been a fantastic result for the Basin’s waterbird populations and for water management in the Murray-Darling Basin,” UNSW Centre for Ecosystem Science Research Fellow Dr Kate Brandis said.

“The fact that we can actually get enough water for the environment to stimulate the birds to breed and mimic a flood is really promising.”

Dr Brandis said the water had supported the breeding of many waterbirds, including a significant colony of 36,000 straw-necked and glossy ibis.

“I’ve seen royal and yellow-billed spoonbills, cormorants, Australasian darters, rufous night herons and pied stilts,” she said.

“Importantly, a number of lesser-known or threatened waterbirds also benefited including great egret, great crested grebe, and the endangered Australasian bittern.”

More than 15,000 hectares of wetlands in the Gayini system were inundated by the water for the environment release, as well as a similar area in the adjoining Yanga National Park, reaching as far as Yanga Lake in the lower Murrumbidgee Floodplain system near Balranald.

NSW Department of Planning, Industry and Environment Senior Environmental Water Management Officer, James Maguire, said the water for the environment release also supported improved aquatic vegetation growth and floodplain wetland health.

“It also created opportunities for native fish, turtles and frogs – threatened southern bell frogs in particular – to breed and move,” Mr Maguire said.

“The population growth in Southern Bell Frog in the Gayini wetlands has been another fantastic outcome. Water for the environment has been strategically used for many years and we are finally seeing this threatened species in great numbers across dozens of wetlands from Gayini over to Yanga National Park.”

Dr Brandis said even larger waterbird breeding colonies typically establish following high rainfall that leads to natural flooding.

“These birds only breed when flooding conditions are right,” Dr Brandis said. “What would normally happen is we would have lots of rain, a big flood, and then the birds would start breeding. Then we would use environmental flows to either extend the flood duration or top up water levels in colony sites.”

She said this event is special because all the water that is currently in the wetlands has come from water for the environment – a component of water that is kept in dams and is marked for environmental use only. 

“The event has demonstrated that we can help support smaller-scale bird breeding events in between the larger breeding events that are supported by floods,” Dr Brandis said.

“The ‘ticking over’ of the system through the use of water for the environment in between larger floods can be critical for some species.”

The waterbirds nest in flooded vegetation and need the water to stay stable, she said.

“If the water levels drop too quickly, they will abandon their nest. So once they start nesting there's pressure to make sure they stay and finish their nesting and fledge their young. And so water for the environment continued to be provided until after the breeding season.”

Gayini, an extensive wetland complex between Maude and Balranald in south-west NSW, is an area of Murray-Darling Basin with state, national and international conservation significance.

It is the largest remaining area of wetlands in the Murrumbidgee Valley, within the southern Murray-Darling Basin and provides feeding and breeding habitat for many different species of freshwater birds.

Water recovery for environmental use was a policy that was introduced by the Murray-Darling Basin plan in 2012.