It’s hard to believe, but nearly a quarter of a billion metric tons of plastic debris is floating in the world’s oceans. Waves and sunlight combine to break the stuff into small pieces that, sadly, are readily consumed by many seabirds, with disastrous effects.

It has long been assumed that floating plastic might look like food to ocean-patrolling seabirds, but researchers at the University of California, Davis, have learned that’s not the case. In a paper published recently in Science Advances, they explain that odor, rather than appearance, likely provides the most influential signal that prompts seabirds to eat plastic.

Albatrosses, petrels, and shearwaters are known as tubenoses because of their prominent nostrils. Possessing an extremely keen sense of smell, the birds are attracted to the odor of dimethyl sulfide (DMS), a sulfur compound created when phytoplankton (microscopic marine plants) are eaten by predators such as krill. The small crustaceans are a favorite food of many oceanic birds. Thus, the smell of DMS provides a strong foraging cue to seabirds that specialize in eating krill and related phytoplankton grazers.

In a study, the researchers exposed plastic beads to real-life ocean conditions. The beads were made of the same types of plastic found in the ocean: high-density polyethylene (used in many food containers, such as milk jugs), low-density polyethylene (grocery bags), and polypropylene (yogurt and similar containers).

After just three weeks in the ocean, all the beads gave off DMS at levels that had previously been found to be detectable to seabirds. Beads that had not been exposed to the ocean did not. Plastic debris, write the researchers, are colonized readily by micro-organisms that produce DMS, and trigger foraging in susceptible seabirds. The species most at risk include Sooty and Short-tailed Shearwaters and other burrow-nesting tubenoses.

It’s hoped that understanding the attraction of plastics to seabirds and other marine life will inspire strategies to reduce the threat posed by increasing plastic pollution. — Julie Craves

A version of this story appeared in the January-February 2017 issue of BirdWatching, on sale now at Barnes & Noble and other newsstands.

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Originally Published January 20, 2017