Seabirds spreading plastics pollution through droppings, study suggests
Some of that plastic floating out to sea is coming back to land in the droppings of birds, a new study says.
Jennifer Provencher, a biologist at Acadia University, was part of a team of researchers looking at the issue among seabirds in northern Canada.
She said most research to this point has been looking at how birds are eating and retaining marine plastic in their stomachs, but that led to the question of what it means for the birds and what happens to the plastics from there.
“Does it stay there a long time, do they get rid of it through regurgitation or somehow else?”
That led her and her team to start looking further past the stomach.
“One of the things we were interested in was, what are they pooping out,” Provencher said.
“For other chemicals that go in, we know a bird might metabolize it and change it into something else, or excrete it, or have it in it its eggs or feathers, but don’t know that about plastics. We know that plastics go in, but we don’t know what happens to it.”
She said some birds used in the study had plastic in their stomachs but not in their guano, and for others it was the opposite, while some had both.
“What the study is telling us is that birds are broadly pooping it out even when we don’t see plastics in their stomach,” she said. “So … when those birds are colonial and nest in large numbers, in some cases at the level of tens of thousands of birds, the real question of our finding is what does that mean from a colony impact?”
She said it’s not surprising to see that birds are excreting
plastics, “but the next question is what does that mean when you have a lot of poop coming out in one place.”
“We think about plastics going out into the ocean and often think about these big gyres floating around out there, but when we start factoring in that migratory birds may be feeding in the gyres and flying into different regions, and regurgitating or pooping out plastics, the birds are actually moving plastic around the landscape.”
Provencher said that raised questions about the impact on other species in the area or terrestrial ecosystems.
“The plastics that go into the marine environment are clearly not staying in the marine environment.”
The pieces of plastic being passed by the birds are usually one millimetre in size or micro fibres, compared to one to two centimetres in the stomach.
“They’re breaking them down, then depositing them. They pick the bigger pieces up in the ocean, and over the natural course of their digestion over time they’re pooping out these smaller pieces.”
The ingestion happens when the birds mistakenly take in microscopic pieces when they are feeding, eat fish that may be carrying plastics themselves, or mistake a piece for food.
“The findings mean that plastic pollution could be more widespread and more dense in areas not previously expected, like in the north or along coastlines. It could be on the ground around colonies, or washing back into the ocean.
“You may find that bivalves like clams or mussels right beside a colony of birds may have higher levels of micro plastics. That’s something people are really thinking about today,” Provencher said.
She said it may not have health effects, but for people who monitor plastic levels in their local shellfish, they could have different test results in shellfish near a colony than further down the coast.
“Understanding what that kind of halo of plastic could look like might actually help aquaculture and others plan or understand how plastics might be exposed to their (operation).”
This summer, the researchers are following up on their findings by going to a bird colony in the Arctic to take air, water, sediment and bivalve samples in and around a bird colony, as far out as 10 km away.
“Based on our understanding, it is likely there is a halo of plastics around some of the bigger bird colonies, but it could be a very tight one, or it could be 500 metres or two kilometres, depending on the winds and the local conditions.”
She said beside aquaculture, knowing how far out the plastics spread from a colony can help people harvesting bivalves and help plan monitoring programs.