These birds are keeping a record of humanity—one wrapper at a time
An advertisement for the 1994 World Cup, fast food wrappers, COVID-19 masks—what birds used to build their nests reflects a world with more plastic.
Coots, rotund black waterbirds with big feet, don’t seem like they’d run the waterways. But in Amsterdam, they’re the “canal gangsters,” territorial and tenacious. They moved in from nearby farms more than thirty years ago, and they’ve toughed it out even in the dense urban core.
Scientists are researching how coots and other birds adapt to urban environments and whether that move is even a good thing.
Now, a new study unravels thirty years of plastic trash in one of the city’s biggest coot nests, revealing when coots build and breed in the city.
One particularly large nest documented 30 years of coots living in the red-light district. The oldest item in the nest was a Mars bar advertising the 1994 World Cup; the newest, a protein bar wrapper. Candy packaging, McDonald’s sandwich wrappers, and face masks represented the years in between, the latter correlating with the COVID-19 pandemic. Similar face mask layers were also found in other nests.
(Related: Gulls Be Gone: 10 Ways to Get Rid of Pesky Birds)
By dissecting the plastic stratigraphy found in the birds’ nests scientists say it’s not just birds they learn about, but humans too.
LIMITED TIME OFFER
Coots take on the concrete jungle
The Netherlands’ capital city has concrete canals, throngs of tourists, and little vegetation. Unlike the idyllic farms and wetlands that surround the city, it’s not the most appealing spot for a coot looking to nest.
Nevertheless, the birds arrived in the 1980s.
“A few brave ones must have been exploring and ended up in the heart of the city,” said Auke-Florian Hiemstra, a biologist at the Naturalis Biodiversity Center in the Netherlands who led the study.
The coots persisted. They began building nests with whatever they could, and that mostly meant trash, from food wrappers to condoms. Today, there are at least 200 coots in the city, Hiemstra estimated. Their messy nests dot docks, pilings, and boats, to the owners’ chagrin.
Hiemstra wondered what the plastic nests of Amsterdam’s coots could tell him not only about the birds’ behaviors, but also about humans.
Curating the Anthropocene
Hiemstra his colleagues collected 15 abandoned coot nests from around Amsterdam. In the nest with the longest and most dateable history, researchers spent slow hours dissecting the nest layer by layer, examining each piece of trash for clues to its age, such as expiration dates or old logos. Once they completed their stratigraphy, they compared when they thought nest-building had happened to Google Street View, first available in 2008, from the nest locations.
“I was studying all the garbage so intensely, especially McDonald’s,” which contributed a significant portion of the dateable trash, Hiemstra said.
Their plastic-based nesting timeline matched up with street imagery. In one year, they could see a coot on the nest; in another, the nest was clearly built up with plastic, and people sitting nearby were eating food with disposable packaging. That gave Hiemstra confidence that his inferences about nesting patterns were accurate.
Studying nests is one of the only ways biologists can study bird behaviors without directly observing them, and opportunities to granularly dissect and date a nest like Hiemstra did are rare, said Dominique Potvin, a behavioral ecologist at the University of the Sunshine Coast in Australia who was not involved in the study.
Potvin’s previous work found that plastic begins appearing in nests around 1950, when plastic use ramped up worldwide. (As newspapers declined, so did their presence in nests, removing useful, obvious dates.)
“The fact that you can look at trends over time is really neat,” Potvin said. Other birds, such as spoonbills, thrushes, and gulls, use plastic for their nests — “it’s a global phenomenon,” she said—but she’d only seen similar nest stratigraphies studied in one other species, bowerbirds.
Still, only about five percent of the material in the large nest was dateable, so Hiemstra still has questions. For example, it’s hard to confirm whether thicker layers of plastic correlate with more foot traffic. He’s also set on finding older nests of other bird species that used plastic, perhaps as far back as the 1950s.
Since his study published, archaeologists have reached out to Hiemstra, excited by the possibilities of plastic nests as records of human activity. “Many never really thought about these bird nests as being archeological deposits,” he said. “Sadly, in the Anthropocene, they are.”
Adapted, but trapped?
Both Hiemstra and Potvin wonder whether plastic nests are helping or harming coots. Plastic nests last longer than natural nests, but that may not mean better protection from predators or the elements. The birds could get tangled in them, especially in items with strings, like face masks. They could choke or suffer internal damage if they eat the trash. And harmful chemicals could leach out.
There’s also the question of whether it’s good that the birds have adapted to live in the city, with its many threats.
“On the one hand, it’s great that they’re able to persist in urban environments and environments we’ve changed, because we’re changing so much of the world,” Potvin said. “But we do see that they can suffer.”
Polluted air and water can impact their health, and if new foods alter their hormones, their reproductive success can drop.
Hiemstra and his collaborators plan to keep studying the pros and cons of plastic construction, and he’ll keep looking for coot nests with dense plastic records like those in the study. The plastic in nests is “kind of a mirror,” Hiemstra said. “It really tells us how humans are treating the environment.”
