It's approaching high tide and the sound of water rushing through a rock wall drowns out the chirping of small birds resting on the tidal flats.
Key points:
- An artificial roost has been installed in the Bundaberg region to offer habitat to critically endangered shorebirds
- Some shorebird populations have declined by as much as 80 per cent in the past 30 years
- Urban sprawl and human disturbance are contributing to the decline
As the water level rises, a line of black floating pillows attached to orange buoys rises too.
The peculiar structure nestled among the mangroves is an artificial roost, the first of its kind to be installed at Queensland's Barubbra Island, off the coast of Bundaberg.
The mesh, oyster shells, foam and zip ties may look like drifting rubbish, but it is a potentially life-saving structure for critically endangered birds.
The roost offers much-needed habitat for migratory shorebirds that have flown thousands of kilometres from breeding sites in Russia and China to the Queensland coastline.
This one, installed by the Burnett Mary Regional Group, is part of a trial hoping to boost the birds' declining populations.
"[The roosts] go up and down with the tides, so they will rest on the sediment at low tide and float at high tide," project officer Samuel Groom said.
"When the bags sit on the sediment, [the birds] can feed around it, so they hopefully don't have to travel far.
"Which means they spend less energy, which means they have more energy to fly back to Siberia or China or wherever they go to breed."
Over time, as the bugs and sea creatures the birds feed on make homes in the oyster shells, it also becomes a valuable food source.
Worldwide decline in species
Several critically endangered shorebird species nest in the region, including the bar-tailed godwit, curlew sandpiper and eastern curlew.
The federal Department of Environment and Water said up to 2 million shorebirds flew more than 9,000 kilometres from the Northern Hemisphere to Australia each September.
According to Birdlife Australia, there are more than 35 species of migratory shorebirds coming to Australia that need to increase their body mass by up to 70 per cent to sustain them on their northern migration.
"These birds are seeing a massive decline worldwide," Mr Groom said.
"They migrate down a very busy area of coastline … so a lot of space that was previously used for feeding and resting, which we call roosting, is being taken away."
More action needed
Birdlife Australia volunteers, such as retired physician and bird expert Chris Barnes, will monitor the number of shorebirds using the new roost.
"The rate that we're losing habitat is probably greater than the amount we're gaining from small wins like this," Dr Barnes said.
"They need all the help they can get."
Dr Barnes said shorebird numbers had fallen by up to 80 per cent in the past 30 years, and while artificial roosts were part of the solution, more action would be needed to arrest the decline.
"We've got to preserve the places we have, be more sensitive with development, leave places for the birds and protect high tide roosts," he said.
"Some people believe we're just documenting an extinction, and an extinction of any species is a great loss.
"We have the chance to protect them and keep them going."
Rafts from an unlikely source
The roost is made out of plastic diamond-mesh "pillows" filled with oyster shells that were originally designed for low-impact oyster farming.
When volunteers for Birdlife Australia noticed migratory birds roosting on floating oyster farm pods, the idea was born.
Secured to a line and anchored into the sand, they offer a low cost, semi-permanent option with little impact on the surrounding environment.
Barubbra Island isn't the only place to have an artificial roost using this method.
The structures have also been installed at three sites in New South Wales's Hunter region and at Port Phillip Bay.
While the sites have attracted a handful of target species, early reports suggest there are natural roosts the birds prefer.
But Mr Groom said it was a different story for a trial in South Korea.
"They saw really high success, upwards of 500 birds being on a single roost," he said.
But he said it was a waiting game to find out how successful the new roost would be.
"We're just dipping our toe in at the moment to see if this will be a viable option."