"These seabirds actually use odours to find their way around in the world and to find food", Matthew Savoca, of University of California, Davis, told the BBC.
So the algae cling to the plastic, and when the krill eat them, the algae scream - chemically, that is.
As plastic floats in the ocean, it accumulates a host of organic matter, including that stinky sulfur compound known as dimethyl sulfide, or DMS.
It might sound weird, but these birds are putting themselves in harm's way by eating these poisonous plastics because they simply smell appetizing.
Seabirds eat plastic because it smells terrible.
"Plastic might not only be visually confusing for these birds, but chemically confusing", Savoca said. In this case, however, the smell was released by algae that coated the floating plastic. The scent elicits a feeding response from seabirds, especially species that heavily rely on their sense of smell to find food.
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.
It had been suggested that perhaps the plastic simply looked like food to marine animals (as it's not just birds nibbling on the trash). The beads were made up of poly-propylene, low-density polyethylene and high-density polyethylene. "Our work does not disprove that plastic might also look like food to some marine animals that eat it", Savoca explained.
They feed on swarms of krill - tiny crustaceans that swirl near the surface of the ocean - and their relatives.
They analyzed the plastics at the UC Davis Robert Mondavi Institute for Wine and Food Science, where researchers are more accustomed to testing wines and whiskeys than plastic trash. The findings help clarify why birds like the albatross and petrels (tube-nosed seabirds) are among the birds most significantly impacted by plastic ingestion. After a while, the plastic may take on the tasty chemical profile, attracting seabirds. These beads, which were placed inside mesh bags and tied to an ocean buoy, were collected three weeks later.
And they say it might be possible to develop plastics that either do not attract algae or break down more quickly in the environment.
It is also produced in the oceans through the breakdown of microscopic algae or phytoplankton, which collects on plastic. For example, Savoca says, some scientists said perhaps sea turtles were eating plastic bags because they looked like jellyfish in the water. But he says the biggest priority should be keeping plastic out of our waterways in the first place.
"[The study] provides a salient mechanism for how this group of birds might be detecting plastic and consuming it", Nevitt said.