A flesh-footed shearwater, a grey and black seabird, sits on a blue water looking towards the left.

Birds provide a vital link between the oceans and the land as they move key nutrients between environments ©Ed Dunens/Flickr CC BY-2.0

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Hundreds of thousands of pieces of plastic are brought back onto land by seabirds

Seabirds on a remote Pacific island have been found to bring on average 688,000 pieces of plastic back onto land every single year.

It is not fully known how this cycle of plastic - from land to sea and back on land again - affects the plants and animals that live in the forests in which the birds breed. 

Seabirds are an integral link between ocean and land. As they feed at sea then return to the coast to breed and raise their young, they provide a major mechanism for nutrients to return to land.

These birds are also some of the key indicators of the health of the oceans, particularly when it comes to the amount and distribution of plastic pollution that is now known to be found throughout every major body of water.

This is because many species of birds will accidently eat pieces of plastic as they mistake it for food. In the same way they bring nutrients back to the forests in which they breed, they are also bringing some of this plastic.

Dr Alex Bond, Senior Curator of Birds at the Museum, has been involved in a project led by PhD student Megan Grant from the University of Tasmania to document just how much plastic is being brought back to land by birds.

A view of Lord Howe Island, with green forest in the foreground leading down to a yellow beach and blue ocean. In the background, mountains rise into low hanging cloud.

On the surface Lord Howe Island may look pristine and untouched, but actually the birds that breed on it are some of the most plastic polluted birds in the world ©Alex Bond

'What we wanted to do was to try and understand the dynamics of seabirds and plastics on Lord Howe Island by figuring out how much plastics the birds were actually bringing back to the colony,' explains Alex.

'And it is pretty shocking. It is much more than we thought it would be.'

The results are published in the journal Environmental Pollution.

The world's most contaminated birds

The ocean is awash with plastic - large, conspicuous pieces (such as fishing gear) floating on the surface, smaller chunks like bottle caps and bags, tiny pieces of microplastic that are almost invisible to the human eye, and everything in between.

This sinister soup of plastic is pervasive, with synthetic material having now been found in almost every single part of the planet's oceans. Even deep-sea fish living at unfathomable depths off the coast of remote islands have been found to contain tiny plastic fibres.

Some of the most plastic contaminated birds in the world are a population of seabirds known as flesh-footed shearwaters that live on the isolated island of Lord Howe, some 600 kilometres off the eastern coast of Australia. These birds breed in a colony of around 22,000 pairs.

While on the surface this tropical island looks pristine, a closer look reveals that the palm forests where the shearwaters nest are speckled with bright, colourful plastic among the leaf litter.  

The forest on Lord Howe, with a large brown trunk in the right of the picture, green bushes in the background, and brown and yellow leaf litter on the floor.

The shearwaters feed at sea but nest within the forests of the island, where they bring back plastics when feeding their chicks ©Alex Bond

'What happens is that the parents go out and forage in the Tasman sea, picking up fish, squid and plastics to bring it back to feed their chicks,' explains Alex. 'Some of the chicks containing this plastic will then die, while when other chicks leave they will regurgitate a pellet of indigestible material.

'That is how all this plastic is found lying on the forest floor.'

This got Alex and his colleagues wondering just how much plastic these seabirds are bringing back to land from the oceans.

The plastic cycle

By mapping out plots within the forest, removing all previous plastic and counting each year how many new pieces turned up, Megan and the team were able to calculate just how much material was being deposited within the breeding colony.

The results shocked the researchers.

Every year, they estimate that the shearwaters bring back and deposit on the island around 688,000 pieces of plastic, weighing roughly 165 kilograms. This works out at about 30 pieces of plastic per breeding pair per year.

The likely impact of this huge amount of plastic is still not known but is something that Megan will be exploring during the next few years of her PhD. 

An array for mulit-cloured plastic pieces laid out on a piece of white paper towel.

The birds eat a variety of plastics ranging in size from a few millimetres to a few centimetres long ©Alex Bond

'In the forest, it mostly it stays on the floor,' says Alex. 'But these birds are burrow breeding species, so some of it gets cycled and mixed in with the soil.

'You have bird species found nowhere else in the world, such as the Lord Howe currawong and the Lord Howe woodhen, which undoubtably poke and prod the plastic. But we haven't looked at these species yet, so we don't know if they are at risk or not.

'But it is not just the plastic itself - it is all the chemicals that come with it. What are these doing to the invertebrate fauna or to nutrient cycling?'

Previous research conducted by Alex and his colleagues has already shown how plastic in the stomachs of birds alters their blood chemistry, which in turn could have knock-on effects on their overall health. It will be important to see if a similar situation is playing out within these forest ecosystems.

It also highlights a relatively unknown cycle that is moving plastic around the world.

Plastic is made and largely used on land, enters the ocean and then is picked up and brought back onto land, in many cases far from where it was originally used. This also raises the question of how migratory birds may be transporting manufactured materials to places usually seen as remote and untouched.

'This is one of the biggest seabird mediated movements of plastic that we know of,' explains Alex. 'But that's not to say it is unique.

'This will be happening in many other places, like with the albatrosses on Midway Atoll, for example. There are more albatrosses and they generally have more plastic by volume in them than the shearwaters on Lord Howe, so you then wonder how much plastic is being deposited onto Midway every year.

'And that's just one seabird island.'