Brown boobie sitt on nest made of plastic

Brown boobies nest on the ground using whatever material they can find, including marine debris © Grant et al. 2018

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Seabirds in the Pacific are using plastic to build nests

As brown boobies incorporate materials they find in the environment into their nests, research has found that the birds can act as indicators of the extent of plastic pollution in the tropics.   

We know that marine debris has become pervasive over the last few decades. From chunks of polystyrene on ice floes in the Arctic to a plastic bag found at the bottom of the Mariana Trench, nowhere has been left untouched by human waste.

But assessing the real scale of the problem over vast tracts of ocean is often difficult.

One way to overcome this is to look at wide-ranging marine organisms that can act as indicator species, also known as sentinels, which can give us an idea as to the health of the oceans.

In a new study published in Marine Pollution Bulletin, researchers from both the University of Tasmania and the Museum have studied the amount of plastic found in brown booby nests right across their range from the western coast of Australia to the eastern coast of Brazil.

They found that when plastic debris is available to use as a nesting material, the birds will invariably use it, supporting the case for using them as indicator species.

Sentinels of the ocean

In the northern hemisphere there are a few species of bird that can be used as indicator species. Around the UK, the northern fulmar has been used for decades to assess ocean plastics as the birds have unfortunately been found to feed on it.

In the southern hemisphere, however, things aren't as straightforward.

A booby nest made from leaves

Normally boobies will make nests out of leaves and seaweed © Grant et al. 2018

Dr Alex Bond, a Senior Curator of Birds at the Museum and co-author of the recent paper, says, 'We lack effective sentinel species in the tropics.

'Brown boobies nest across the South Pacific, the Caribbean and the South Atlantic. So we wondered whether these could be some sort of indicator of the extent of ocean plastic.'

The birds build little nests on the ground in colonies, often along beaches. Usually they will create the nests using what they find on the shoreline, such as seaweed and leaves. But in recent times this has started to change.

'We noticed back in 2014 that quite a lot of booby nests had plastic in them,' says Alex. 'From fishing rope to hard pieces of plastic, you name it, the nests contained a whole variety of debris.'

Preferred plastics

This led the University of Tasmania's Megan Grant to investigate whether the nesting material of the boobies could be used as an indication of the local extent of marine plastic.

Megan collected data on the amount and type of debris found in the boobies' nests from 18 different locations right across the birds breeding range. She could then compare what was found in the nests to the amount and type of debris found washed up on the adjacent beaches.       

'The nesting material typically derives locally, so boobies will get their material from the beaches they nest on or very close offshore,' explains Alex, 'and what we found was really interesting.

'At some sites every nest had plastic in them, while at others none of the nests had plastic. This implies that the birds are responding to the amount of plastic that is available locally.'

But that isn't the whole story.

Brown booby sat on its eggs

While the plastic might not affect the birds, it is symptomatic of what is going on in the oceans as a whole © Grant et al. 2018

When the team compared what debris was found on the beaches to what the birds were using as nesting material, there was only a slight overlap. This suggests that the boobies had their preferences.  

'It wasn't consistent across all the sites,' says Alex. 'Some colonies preferred green ropes, others white fragments. That variation among the sites is one of the more fascinating aspects.'

What might be driving this variation is still not really understood. For some seabirds in the UK it has been suggested that the birds select green rope due to its similarity to seaweed. But the truth is that we know very little about colour perception in seabirds and so what might be driving these choices.

The plastic problem

It will come as no surprise that the plastic problem pervading the oceans is becoming more visible and more dangerous to marine life.

'In the worst case scenario, birds using plastic to build nests can lead to entanglement,' says Alex. 'In the UK, for example, we see gannet chicks getting caught and then dying. This is either through being tangled and falling off the nest or getting strangled.'

While for the brown boobies the impact of building their basic nests with plastic might not be so great, these birds are yet another indication that we are rapidly changing the oceans and need to do something about it soon to prevent the further loss of species.