Auke-Florian Hiemstra, a doctoral student at the Naturalis Biodiversity Center in the Netherlands, has spent years studying how birds use human materials in their nests.
Much of his research involves collecting abandoned coot nests and painstakingly logging their contents: drug paraphernalia, earbuds, windshield wipers. “Everything that ends up in the canals in Amsterdam most likely finds its way to a coot nest,” he said.
But in late 2021, he found a piece of trash, buried at the bottom of a large coot nest, that stopped him short: a wrapper from a Mars bar promoting the 1994 World Cup. “That really gave me goose bumps,” he said. “Suddenly we had this big realization. Like, these deeper layers are actually older layers.”
Fittingly, the nest had been built just outside an archaeological museum, atop a metal pipe jutting above the canal’s surface. Mr. Hiemstra wondered if, like an archaeologist, he could peer back in time by dating the artifacts he found in each layer of the nest.
All told, the nest contained 635 artificial items, including foil from cigarette packages and a ticket to Amsterdam’s National Maritime Museum. Roughly one-third of the items were related to food. Mr. Hiemstra carefully examined each object for an expiration date that might indicate roughly when it had been added to the nest.
These were estimates. Highly processed foods could have expiration dates that extended for months or years after when they were eaten. And any given piece of trash might have lingered for a while before a coot added it to its nest.
For a recent paper, published in the journal Ecology, Mr. Hiemstra and his colleagues documented every roughly datable item they found in the nest, opening a small window onto the history of the city’s avian and human residents.
Near the top of the nest was a bounty of candy bar wrappers (including one from a Bounty chocolate bar) bearing 2021 expiration dates, as well as packaging from a protein bar set to expire in 2022.
There was also a thick layer of surgical face masks, which was likely to have been added to the nest sometime after the Covid-19 pandemic began in 2020.
“Face masks, of course, are like a little mattress,” Mr. Hiemstra said. “They’re soft and they may be very warm.” But they can also be dangerous, he added, if the birds become entangled in the masks’ elastic loops.
Much of the food packaging came from items with long shelf lives. But the scientists also found a carton of milk that must have been purchased — and, one hopes, consumed — close to its expiration date of May 2013.
Mr. Hiemstra also found an abundance of trash emblazoned with the logo of a single brand: McDonald’s. The sauce containers were easy to date, as they bore expiration dates on their lids.
A faded plastic foam McChicken box was trickier, bearing only a 1996 copyright date.
“I was in a very deep rabbit hole at a certain point, just talking with these people who were vintage McDonald’s collectors,” Mr. Hiemstra said. “It really felt like a kind of McDonald’s archaeology.”
Ultimately, he was unable to pinpoint a clear date for the container, although the item remained an evocative artifact. “We found the packaging of one bird, a McChicken, as part of the nest of another bird,” he said.
And then, in a deep, mud-covered layer of the nest, which emitted “a distinct canal smell,” was the Mars wrapper that started it all. It carried a FIFA logo with a 1993 copyright and promoted the 1994 World Cup, which took place in the United States and was won by Brazil.
Mr. Hiemstra had no memory of that World Cup; he was born in 1992. “So this wrapper was just as old as I am, almost,” he said.
The nest is a testament to the ingenuity and resourcefulness of wild animals in a rapidly changing world. “It really tells the story of the Anthropocene, but then from the bird’s perspective,” Mr. Hiemstra said.
It’s also a physical embodiment of how profoundly humans are reshaping the environment, he added, and how long-lasting the effects can be.
Roughly three decades ago, some weary commuter or ravenous teenager ordered a McChicken sandwich and then tossed out the box that it came in. “Just one meal from one person — the packaging is still here,” Mr. Hiemstra said. “A bird has been breeding on it for 30 years.”