Seabirds are swallowing shocking amounts of plastic, with hundreds of pieces found in one bird

Plastic pollution in the ocean is often measured by asking a simple question: how many animals have swallowed plastic?

That number matters, but a long-running project on Australian seabirds shows that it can hide a much more serious change.

For Sable Shearwaters on Australia’s Lord Howe Island, the percentage of young birds carrying plastic has stayed fairly similar for years.

What has changed is the amount inside the worst-affected birds, with some recent fledglings carrying hundreds of pieces.

That matters beyond one seabird population. The findings show how an environmental problem can become much worse even when the most familiar measurement barely changes.

Why these birds matter to people

Seabirds spend much of their lives feeding across large areas of the ocean, which makes them useful indicators of what is happening far from shore.

If plastic is becoming easier for these birds to encounter, their stomach contents can reveal changes that beach surveys alone may miss.

Sable Shearwaters breeding on Lord Howe Island travel widely across the Tasman Sea to find food for their chicks.

That means the plastic arriving at the colony may have been collected hundreds of miles away, not just near the island itself.

For people, the bigger lesson is about how environmental problems are measured.

A pollution problem can look stable if researchers only count how many animals are affected, even while the amount of pollution inside individual animals becomes much worse.

A long record reveals change

Researchers followed Sable Shearwaters from 2010 through 2026. Across much of that period, roughly 75% to 85% of sampled fledglings contained plastic.

At first glance, those numbers do not suggest a dramatic change. The share of birds affected stayed within a fairly similar range for many years.

But the team also looked at the 10 most heavily affected fledglings from each season.

That revealed something the simple percentage could not show: the birds carrying the largest plastic loads were swallowing much more than before.

In the early years, 2012 stood out as a particularly bad season, followed by several years with much lower plastic loads. The pattern jumped up and down rather than rising smoothly.

Plastic loads suddenly became extreme

Then the records started breaking.

One fledgling sampled in 2023 contained 403 pieces of plastic. Another in 2024 contained 407 pieces.

In 2025, one bird contained 894 pieces weighing about 2.27 ounces (64.21 grams). The following year, another contained 644 pieces weighing 2.38 ounces (67.4 grams), the highest plastic mass reported in the paper’s results.

Dr. Alex Bond, principal curator of birds at the Natural History Museum and a co-author of the work, said the team had once believed much lower levels represented the physical limit.

“In 2012, we found a sable shearwater with 276 pieces of plastic in it. We thought this was the worst-case scenario, as a fledgling of that size couldn’t survive eating any more,” Dr. Bond said.

“We were wrong. From 2023–2026, the record for the most plastic ingested by these birds has been broken year after year. The plastic crisis is only getting worse, but we’re acting nowhere near fast enough to try to tackle it.”

Some plastic types also increased

The researchers did not only count fragments. They also tracked recognizable items, especially bottle caps and small industrial plastic pellets known as nurdles.

Both became more common in heavily affected birds during recent years. Nurdles were especially unusual because they sometimes appeared in large numbers even when total plastic levels were relatively low.

That suggests different forms of plastic pollution can rise and fall independently. A spill could help explain a sudden burst of nurdles, but the paper could not identify a single source behind the repeated increases.

This matters because some types of waste are easier to target than unidentified fragments. Measures that keep bottle caps attached to bottles, for example, could reduce the number of loose caps entering the environment.

Short projects can miss the problem

One of the most useful parts of the work had little to do with birds themselves. The team asked what conclusions they would have reached if the project had lasted only a few years.

The answer changed dramatically depending on the time period.

Some three-year windows suggested plastic exposure was falling. Others showed no clear change, while others pointed upward.

Five-year periods were still inconsistent. But when the researchers looked across longer 10-year windows, the pattern became much clearer, with later periods showing a significant increase in severe plastic exposure.

That is important for anyone trying to understand pollution, climate change or wildlife decline. Nature does not always change in a smooth line, so a short project can capture a temporary dip and mistake it for improvement.

Limitations of the study

The project does not show exactly why the birds are swallowing more plastic.

Earlier work has found that chick body condition has declined, and the authors suggest that adults struggling to find natural food may become less selective, but this paper did not directly test that explanation.

The researchers used two ways to collect plastic.

Live birds had their upper stomachs flushed, while dead birds could be examined more completely, and stomach flushing can miss plastic in heavily affected birds.

The annual sample sizes also varied. Only two birds were sampled in 2020 because of the COVID-19 pandemic, while other years included well over 100 birds.

Most importantly, the 10 worst-affected birds do not represent the average chick. They were chosen specifically to show what was happening at the extreme end of exposure.

Better measurements show the risk

The main lesson is simple: counting how many animals contain plastic is not enough.

A population can show a similar percentage of affected birds for years while the most heavily exposed animals become far more contaminated.

Without measuring the number, weight and type of plastic, that worsening problem can stay hidden.

For people trying to understand what is happening in the ocean, that makes long-term monitoring especially valuable.

It can reveal changes that short projects miss and can show when an environmental problem is becoming more severe even before the basic percentages move very much.

The study is published in the journal Earth’s Future.

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