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99 percent of all seabird species will have plastic trash in their bellies by 2050. But why do seabirds have such an apparent appetite for bottle caps and wrappers? According to researchers from the University of California, Davis, “the answer stinks.”

According to the new study published in Science Advances, the birds could be attracted to the smell of algae on the plastic. The researchers found that the algae that cakes much of the sea’s drifting plastic debris releases a chemical sulfur compound, dimethyl sulfide (DMS), which is also released when algae is eaten by krill and other prey of the birds. So, for seabirds, the scent of DMS is – and always has been – associated with food.

“It’s important to consider the organism’s point of view in questions like this. Animals usually have a reason for the decisions they make. If we want to truly understand why animals are eating plastic in the ocean, we have to think about how animals find food,” lead author Matthew Savoca said in a statement.

The scientists made the discovery by placing three different types of plastics in waters off the Californian coast in Monterey Bay and Bodega Bay, which were placed in mesh bags so marine life couldn’t eat them. After three weeks, they took the samples back to the lab and used a chemical analysis that is usually used to analyze scents for fine wine. It was this off-the-wall method that detected the presence of DMS.

Seabirds that have a keen sense of smell for hunting, such as petrels and albatrosses, are the most affected by eating plastics. In fact, birds that track their prey by sniffing for DMS were six times more likely to have ingested plastic.

Sadly, this is an issue that affects all types of marine life, from turtles, to fish, to whales. Early this year, a post-mortem showed that 13 sperm whales that had washed ashore in Germany had plastic trash in their intestines.

Co-author Gabrielle Nevitt warned that some bird species, including petrels and shearwaters, are being impacted by plastic ingestion but are often being overlooked. 

“These species nest in underground burrows, which are hard to study, so they are often overlooked. Yet, based on their foraging strategy, this study shows they’re actually consuming a lot of plastic and are particularly vulnerable to marine debris,” she added.

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