Recordings of endangered bittern bird calls give scientists insight into impacts of floods

June 18, 2023

Key points:

  • Monitoring of the bittern calls show near-record numbers
  • The Barmah-Millewa Forest is home to 30 per cent of the remaining bittern population
  • Researchers had to paddle into the forest after flooding

Recordings of the deep growls or booming calls of male Australasian bitterns in wetlands in southern New South Wales have sparked hope for the recovery of the endangered bird.

It’s estimated there are only 1,300 bitterns left in the wild. The high volume of calls recorded last spring in the bird’s prime habitat of the reedy wetlands of the Barmah-Millewa Forest show near-record numbers.

Charles Sturt University scientist Elizabeth Znidersic said the bittern was so well-camouflaged that tracking its call gave the best insight into breeding activity.

“[It’s] a very low-frequency boom. It’s the males going, ‘Here I am. I’ve got a good call. I’m very fit. I’m very good looking, come and get me,'” she said.

“I think it was an absolutely amazing outlook for the species.”

Racing floodwater

As floods in the Murray River approached the forest last September, Dr Znidersic and her team rushed to place sound recorders.

“We got out there as quickly as we could and we were basically deploying acoustic recorders up trees,” she said.

“Where we would normally walk we actually had to kayak or use a boat.”

The flood was the largest in a decade and water levels in the forest rose and then fell by about 4 metres.

When the research team retrieved the sound recorders months later they were surprised to find that while the calls stopped as the water rose the birds became active as it receded.

“With the flooding event we thought because all the habitat was under water that was probably it for the breeding season,” Dr Znidersic said.

“But as soon as that water level dropped we saw a later-than-normal breeding season begin and the bird started to vocalise for a few months after that peak water.”

To ensure bittern chicks successfully fledged, as it was so late in the season, additional water was delivered into the wetlands.

The NSW Department of Planning and Environment’s Paul Childs said it was a good result.

“This outcome highlights the importance of long-term monitoring that helps to inform the adaptive management of environmental water and site-based management activities such as predator control, which are essential components for building Australasian bittern populations,” he said.