Bird experts say bad weather and ocean warming are possible reasons for hundreds of short-tailed shearwaters washing up on New South Wales beaches.
Key points:
- Birdlife Australia says "wreck" events are "confronting", but not unusual
- It is suspected that stormy weather or an ocean warming event may have caused the deaths
- Some birds are being euthanased and others are being moved to safe places to recuperate
There have been reports of the species, also known as the mutton bird, being found dead on beaches from Coffs Harbour, on the Mid North Coast, down to Shoalhaven Heads.
The birds are returning from the Bering Sea near Alaska to breed in Victoria and Tasmania.
The journey is part of their 10,000-kilometre migration, which takes three or four weeks.
Mick Roderick from Birdlife Australia said it was normal for birds to perish along the way.
"On that epic migration you can imagine that it wouldn't take much for something to go wrong," he said.
"Some of them get very exhausted and then they wash up on our shores.
"We call it a 'wreck' — it can be confronting, but it's quite normal.
"Whether or not it's been exacerbated by humans is up for conjecture."
Differing theories
Parts of the Hunter and Central Coast copped a deluge over the past 24 hours and more than 100 millimetres of rain fell in some coastal areas.
Wildlife ARC Society volunteer Sam Chatfield said the bad weather was the most likely reason for the birds washing up on beaches.
"It does happen every year, it's just that we don't notice it until there's something significant that gets them all in a group like the storms did," she said.
"They do play a part in the ecosystem — the bodies get washed out and eaten by things like sharks."
But wildlife ecologist Jennifer Lavers, who specialises in seabirds, said she did not believe the deaths were due to an isolated storm event because the birds had evolved to survive extreme conditions.
She said it was more likely a giant eddy off the coast of Sydney generated massive sea warming and put regular food sources out of reach.
"These marine heatwaves, or the eddy structures, are basically like forest fires but in the ocean," she said.
"If we think back to the Black Friday fires a couple of years ago, those had very significant consequences for wildlife — not just for the animals that live in the water where the marine heatwave or forest fire is taking place, but animals that interact with that area that rely on it for food."
University of NSW Oceanographer Moninya Roughen said the eddy extended 400 kilometres east into the Tasman Sea and was three kilometres deep.
She said is increased the water temperature by about three degrees Celsius and that warmer water could destroy ocean habitats.
"That's the basis of where we get our fisheries … the habitat dies and the fish disappear," Ms Roughen said.
Mr Roderick said the ingestion of plastic at the start of the journey could also impact the birds.
He said in 2013 hundreds of mutton birds that washed up on beaches were found to have pumice in their guts.
"This stuff was obviously floating on the surface of the ocean and some birds had ingested it," Mr Roderick said.
"Whether or not that accounted for that big wreck, again, we just don't know."
Inundated with calls
Ms Chatfield said crews had been responding to calls for assistance from distressed members of the community.
She said dead birds were being left to wash back into the sea and that dying birds were being euthanased.
"If they look like they're just tired we moved them to somewhere that was a bit protected from the weather and left them so they could dry and warm up," Ms Chatfield said.
"Some of them were even continuing their migration after a couple of hours' rest."
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