Plastic Triggered a New Geological Epoch—and the Evidence May Be in Bird Nests

Plastic may have started a new geological era on our planet, sometimes called the Anthropocene. Hundreds and even thousands of years from now, scientists may date sediment layers by finding bits of old plastic, similar to how today’s archaeologists date excavations by the art styles of ancient pottery. In fact, this has already begun: Researchers revealed the history of bird nests in The Netherlands by scrutinizing plastic litter used in the nests’ construction.

Many different birds, including the common coot, have started incorporating human-made food and drink packaging into their nests. This allowed three biologists to reconstruct the individual histories of dozens of common coot nests in Amsterdam using a simple trick: Reading the expiration date on the plastic.

There’s only one problem—these nests aren’t supposed to have a history, because common coots don’t normally reuse their nests from year to year. As detailed in a study published February 25 in the journal The Scientific Naturalist, not only has plastic turned bird nests into time capsules, but it might also be fundamentally impacting the evolution of certain species.

“The common coot is a wetland bird that in The Netherlands originally built its nests of plant materials which rapidly decay, so coots normally construct a new nest every year. However, as plastics and other artificial, more durable materials are used for nest construction, new behavior, namely, the reuse of nests from previous years, may appear,” the researchers wrote in the study. “This, in turn, may create a history of multiple years of nest use, reuse, and reconstruction to be studied using the stratigraphy of dateable plastic debris in the nest.”

Leiden University’s Auke-Florian Hiemstra collected over a dozen empty coot nests to get to the bottom of the new nesting behavior. Back in his lab, Hiemstra deconstructed and sorted the nests into two piles, one filled with natural materials used in the nests and one that consisted of human-made materials. Many of the human-made materials used in the coots’ nests had expiration or packaging dates that allowed Hiemstra to date layers of the structures very accurately.

“You flip through these nests like through pages of a history book, uncovering the past,” Hiemstra said in a Naturalis Biodiversity Center statement. In one of the most striking nests, Hiemstra counted 635 artificial items, of which 32 were food-related waste with dates going back decades. Almost half of these datable materials were from McDonalds, and they even found a Mars wrapper advertising the 1994 FIFA World Cup in the United States.

“From these dateable items, a picture emerges of what happened at this nesting site over the past 30 years,” the researchers explained. “As the nest was located at a dock for tour boats, which were constantly mooring, the nest could not be deconstructed layer by layer in chronological order. Yet while collecting, we observed recent top layers of facemasks and the deepest layers of nest material showed plastic dating back to the early 1990s.”

Cross-referencing these dates with archived Google Street View imaging confirmed that “Coots were indeed nesting in the years corresponding to the expiration dates found in the nest.”

In total, Hiemstra and his colleagues identified 15 common coot nests whose use of plastic materials pointed to a multi-year existence. They suggest that this new behavior may give the birds evolutionary advantages. For example, coots that simply add more material to previously existing nests have more time and energy to defend their territory and breed than coots that have to build from scratch.

“Layer upon layer, with every new breeding attempt, an accumulation of plastic litter in stratigraphic order is laid down, which forms a historical time series,” the researchers concluded. “The serial deposits, constructed out of artificial material, may not only document the history of a bird nest, but also reflect the history of our Anthropocene Epoch.”

It’s difficult to say how future researchers will interpret our layers of waste, but one thing is clear: Humans are leaving a lasting impact on Earth, one evident in plastic left in everything from birds’ nests to Iron Age archaeological sites.