Broken Secrets

Seabirds Eat Plastic Because it Looks and Smells Like Food

July 7, 2018 at 3:01 am Stephanie Wolek 1 comment

Marine pollution is a well-known, continuous problem in our world’s oceans. Of the types of anthropogenic debris (waste originating from human activity), plastic is perhaps the most dangerous. Few plastics are biodegradable, which means they stick around for a very long time without breaking down. According to NOAA and the Mote Laboratory in Florida, it can take hundreds of years for plastics to degrade. The length of time varies based on the type of plastic, product, and environmental conditions—but that doesn’t change the fact that it takes an average of 450 years for a plastic bottle to break down! A fishing line can take 600 years. Even when they do break down, they release tiny pieces of plastic that seem to persist indefinitely. Even worse, they’re regularly consumed by marine animals—often by accident. This can cause serious health problems, resulting in mortality for a large number of birds and other sea critters.

Recently, a dead sperm whale was found with 64 pounds of plastic and other human waste in its stomach. It’s believed that the large amount of plastic was a major contributor to the animal’s untimely death. Plastics are even polluting the deep ocean, with many deep-sea creatures consuming microplastics (pieces of plastic about the size of a sesame seed or smaller) on a regular basis—including lobsters, crabs, and sea cucumbers. Of all the animals being affected, the worst off are probably the seabirds.

Seabirds have been known to consistently ingest plastics, generally resulting in early deaths for the unlucky fowl. While the exact numbers are unknown, scientists have previously estimated that 80 to 90 percent of studied seabirds have consumed plastic. This includes many endangered and threatened species which are already in decline due to overfishing, chemical pollution, climate change, and other human-driven factors.

So why are seabirds consuming so much plastic? It makes sense that it could all be accidental but they’re consuming marine debris at a faster rate than other ocean animals. Thankfully, marine biology research is beginning to provide some insights into this major conservation problem.

In many cases, the plastic simply resembles the bird’s primary food source. In one Australian study, the researchers discovered that surface feeders were more likely to consume floating objects such as plastic bags and balloons. One species (short-tailed shearwaters), which normally feed on red arrow squid, were consistently eating red and orange balloons—clearly a case of mistaken identity! Shoreline birds were more likely to be found consuming lures and other beach debris. This isn’t the end of the story, however, as a stranger factor is at play.

A later study provided another possible reason for why so many seabirds were consuming plastics and then dying. As it turns out, the plastic doesn’t simply look like food—it also smells like food. Scientists from the University of California placed plastic beads in mesh bags underwater off the Californian coast. Three weeks later, the team returned to retrieve and analyze the beads. The plastic had changed—it was now emitting a new chemical signature. The plastic beads were releasing dimethyl sulfide. In the wild, zooplankton (tiny aquatic animals) release the same chemical as they’re eaten. Unfortunately, zooplankton predators (such as fish) are a preferred food source for many seabirds and these chemicals are how they track their prey. The birds were smelling chemicals that normally led to food—and they were instead greeted with deadly plastic. The groundbreaking study finally explained why seabirds were consuming plastic at a much greater rate than other marine animals.

Seabirds aren’t just accidentally swallowing plastic and other debris, they’re seeking it out because it both looks and smells like their natural food sources. By the time they’ve snagged the trash in question, it’s too late. This, unfortunately, points to only one way of stopping seabird plastic ingestion—we need to stop using so many one-use plastic products while working on ways to break down the plastics that already exist in the ocean. Otherwise, we’re going to lose many threatened and endangered bird species very, very quickly.

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Photo: Peretz Partensky (cc)

Sources: des.nh.gov, des.nh.gov, cnn, plos.org, sciencemag.org, nature.com, noaa.gov

Entry filed under: Animals, Be Green. Tags: birds, plastic, pollution.