Plastic in nests like 'pages of a history book', says scientist

A birds' nest that appears to go back 30 years is helping researchers with a new study.

For the first time researchers have studied the plastic found in birds' nests to work out how old they are.

Using the expiry dates on the layers of plastic packaging biologist and urban ecologist Auke-Florian Hiemstra was able to put together a timeline of the nests.

"Some nests are remarkable time-series: from early 90s fast-food packaging all the way to face masks from the COVID-19 pandemic. We even found a Mars wrapper promoting the USA FIFA World Cup 1994!" Auke-Florian said.

Auke-Florian first started looking at plastic as a historical document while studying the nests of common - or Eurasia - coots in Amsterdam the capital city of the Netherlands.

Coots nests are made up of bits of plastic alongside natural materials like twigs and leaves.

Researchers only collected nests after the breeding season, when coots have discarded their nests.

The main way the researchers were able to work out how old the plastic packaging was, was by looking at the use by dates.

A large proportion of these dateable plastics was fast food packaging.

There were other ways of working out time periods.

A Mars bar wrapper promoted the 1994 FIFA World Cup in the USA, while the upper layers contained face masks, a direct result of the COVID-19 pandemic.

Previous studies have shown how plastic pollution can impact birds with young chicks getting tangled up in string or birds eating plastic by mistake.

An old McDonald's container and a Mars bar wrapper promoting the 1994 World Cup were found in one nest

Auke-Florian says the study reveals how animals unintentionally document environmental problems.

"History is not only written by humans, nature is also keeping score," he said.

Traditionally the coot did not used to reuse their nest because it was made from plant material which would quickly fall apart.

But Auke-Florian discovered that the birds were often reusing the bases of old nests because they were made of plastic which is made not to fall apart.

With one nest "we could see nest upon nest, upon nest upon nest. You can flip through the nest as through pages of a history book!" Auke Florian told Newsround.

The nesting material is deposited in the collection of the Museon-Omniversum in The Hague, where it will be included in the museum's presentation on the Anthropocene.