AUDIE CORNISH, HOST:
Imagine you're passing a fast food restaurant, and you smell hamburger on the grill. You're hungry. So you pull in and eat one and the styrofoam box it comes in. That's kind of like what's happening to some oceanic birds. As NPR's Christopher Joyce reports, scientists think they know why those birds are eating plastic.
CHRISTOPHER JOYCE, BYLINE: It puzzled biologists. Why do sea animals and birds eat floating plastic? Their best guess was it looks like food, but now there's evidence that for a lot of birds, plastic actually smells like food. It all comes down to a common kind of algae floating in the ocean. The algae is food for small animals like krill. When the krill gobble up the algae, the algae emit a chemical - dimethyl sulfide. Biologist Matthew Savoca says it stinks up the place. It's actually a chemical scream.
MATTHEW SAVOCA: The algae are sort of crying out, saying, oh, my gosh, we're being eaten, and can someone please help me?
JOYCE: Now, that may sound ridiculous, but help does come in the form of birds. When seabirds like shearwaters smell that chemical, they know it means tasty krill are in the water.
SAVOCA: Think of it as, like, a dinner bell, right? So if we heard a dinner bell ringing, the dinner bell would signify where we could find food.
JOYCE: At the University of California, Davis, Savoca and his team wondered if birds were eating plastic because there was stinky algae living on it. So they put plastic out to float around in the ocean. Then they took it to the university's food and wine laboratories. This is northern California, after all. They got some weird looks when they stuffed plastic into equipment designed to track chemicals in fine wine, but they did get their answer.
SAVOCA: Sure enough, all this plastic reeked of that sulfur compound, likely due to the algae that coated it when it was out at sea.
JOYCE: So the algae clinged to the plastic, and when the krill eat them, the algae screamed - chemically, that is. The birds smell it, and that's their foraging cue. They scoop up the krill and the plastic. The research appears in the journal Science Advances. Marine ecologist Chelsea Rochman at the University of Toronto says, obviously, eating plastic is not good for the birds, but the plastic also picks up other harmful chemicals that make it even nastier.
CHELSEA ROCHMAN: With plastics, it's a sponge for a lot of the chemicals that are in oil and the chemicals that are washing off from different sources, like pesticides and flame retardants and other industrial pollutants.
JOYCE: Poisoning birds is a problem, but Rochman says biologists suspect that other marine animals, like fish, could also be eating the plastic for the same reason. And that could have consequences for people who eat those fish. Christopher Joyce, NPR News.
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