A 15-year study of sable shearwaters has also shown the bird's complex song repertoire - which helps adults find their way back to their own nesting burrows and chicks - is impaired, reducing breeding success.
The research used the shearwater, which has a 20,000-strong colony on the World Heritage-listed Lord Howe Island in the Tasman Sea, as a case study.
The study's lead author Dr Jennifer Lavers from Charles Sturt University said that average number of plastics the birds were consuming had skyrocketed, leading to increased mortality.
She told AAP that when research on the birds began, their stomachs might contain five pieces of plastic, but now might hold up to 60.
"The challenge has been to link that plastics exposure with population decline," she said.
"So over that 15-year period, we asked the question: who survives and who comes back?
"What we found was if the birds had consumed plastic, their odds of surviving at sea and returning were exceedingly low, and the more plastic they had, the worse the prognosis."
Dr Lavers said that more than 1500 marine, terrestrial and freshwater species were known to inadvertently consume plastics around the globe.
However, she said it was difficult to measure the extent of plastics mortality against other pressures, such as habitat degradation, introduced predators, global overfishing and other extinction drivers.
Lord Howe's remote and otherwise pristine environment made the sable shearwater an ideal subject to tease out the long-term population impacts of plastic pollution.
After hatching on the island, the young shearwaters head out to sea for several years before returning to breed as adults, with parents feeding their chicks plastic waste after mistaking it for food.
This resulted in many chicks experiencing dementia-like symptoms and suffering from a fibrotic disease known as plasticosis, leading scientists to dub them the "walking dead".
"In 80 to 90-day-old seabirds we found signatures of protein change in their blood that is indicative of things like Alzheimer's disease and Parkinson's," Dr Lavers said.
"It is truly remarkable that a three-month-old wild animal could have dementia."
She said proteins in the brain associated with the development of the bird's complex song was also impacted by plastics, making it harder for adults to find their offspring.
When the birds returned from a day at sea to their island burrows, they had to find them and reunite with their chicks amid a din of individual squeaks, hoots and honks.
"What we found was that even if a bird survives all the physical health consequences, its likely future breeding success is going to be impaired," Dr Lavers said.
The research, funded philanthropically and via volunteers, was conducted by applying numbered metal bands to the legs leaving the island for the first time, after checking their stomach contents for plastic.
The research findings come a little over a year after United Nations negotiations for a treaty to curb plastic pollution collapsed in Geneva.
Dr Lavers said a draft proposal released last week had been substantially watered down.
"We need a global plastics treaty that is enforceable, one that is bold, and one with immediate effect," she said.
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