Something Smells: Birds' Keen Sense of Smell Causes Plastic Ingestion

Researchers from the University of California, Davis have discovered that an olfactory cue catches the attention of the birds and convinces them that marine plastic is food. In a recently published study in the journal Science Advances, the reason behind ocean-faring birds ingesting large amounts of plastic has been revealed: marine plastic debris emits the scent of a sulfurous compound that some seabirds have relied upon for thousands of years to tell them where to find food.

"It's important to consider the organism's point of view in questions like this," said lead author Matthew Savoca. A member of the Graduate Group in Ecology, Savoca had performed the study as a graduate student in the laboratory of UC Davis professor and his co-author Gabrielle Nevitt. "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."

To determine the flavor profile of trash, the researchers put beads made of high-density polyethylene, low-density polyethylene, and poly-propylene into the ocean at Monterey Bay and Bodega Bay, off the California coast. Making sure not to add to the marine plastic problem by distributing these three most common types of plastic debris, the scientists placed the beads inside specially sewn mesh bags and tied them to an ocean buoy before collecting them about three weeks later.

Once the plastic was retrieved, it was brought to the UC Davis Department of Viticulture and Enology, a place more known for analyzing wine flavor chemistry than garbage. Susan Ebeler, a prominent food-and-wine chemist, allowed the team to use her analyzer where they discovered that the plastic gave off the odor of the sulfur compound dimethyl sulfide or DMS. DMS, as Nevitt had previously established, is released when algae is eaten by animals like krill, one of the birds' favorite meals. So while the algae do not smell like food itself, it is a chemical cue released by algae that trigger tubenosed seabirds to forage.

"This study shows that species that don't receive a lot of attention, like petrels and some species of shearwaters, are likely to be impacted by plastic ingestion," Nevitt stated. "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."

The scientists believe their study could also open the door to new strategies that address the ocean's plastic problem, which plagues not only seabirds, but also fish, sea turtles, and other marine life.