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New research reveals the impact of discarded plastic materials on young birds—with chicks dying after becoming entangled in synthetic fibers used to build their nests.

Scientists from the University of East Anglia (UEA) examined the impact of plastics and rope in the nests of land-dwelling birds, using white storks as a case study. As is happening in the oceans due to human plastic pollution, they found that discarded synthetic materials can be a serious hazard on land too.

The , published today in the journal Ecological Indicators, found human-derived materials were present in 91% of 568 stork nests monitored in Portugal over four years. During a year of weekly checking, 12% (35) of nestlings became entangled, with many of those dying, often due to injuries such as necrosis and limb loss.

Soft plastic, such as plastic bags, was the most prevalent material and found in 65% of the nests. This was followed by synthetic ropes—the main cause of entanglement—found in nearly half (42%) of the nests.

Baler twine, a slow degrading polypropylene rope, accounted for 63% of the entanglements and was present particularly in colonies surrounded by agricultural areas.

The team, including researchers from the University of Montpellier and University of Lisbon, also found that white stork chicks in nests containing a higher number of ropes were more likely to become entangled and had lower survival rates.

The authors warn that as a common indicator species, the entanglement of white storks, particularly in baler twine, highlights a broader environmental issue not limited to that species or Portugal.

Lead author Ursula Heinze, a postgraduate researcher in the School of Environmental Sciences at UEA, said, "Our findings offer new insights into the extent of nestling deaths caused by entanglement, and highlights the urgent need to remove and replace hazardous materials such as polypropylene baler twine from both agricultural use and the environment, given its harmful impacts on nestlings.

"This study suggests that the threat posed by human-derived materials to terrestrial birds may be far more severe than previously recognized."

Co-author Prof Aldina Franco, also from UEA, said, "This is a serious issue. These chicks get entangled in synthetic ropes when they are very young and the ropes slowly strangle their limbs as they grow, mostly legs and feet, leading to necrosis and amputations. They suffer a horrible death.

"Our paper is really timely, it highlights a widespread issue with poorly quantified consequences. In Ukraine, for example, soldiers are finding nests with fiber optic wires from remote controlled drones. In the UK, several passerines, such as goldfinches and wrens, have also started using different color polypropylene threads to build their nests. People spotting empty nests at the end of the breeding season may have started to notice this.

"We show that the impact of plastic in the nests can be underestimated because the negative effects of the ropes and other human-produced materials tend to happen in the early life of the chicks, at an average age of two weeks, and the deaths can go unnoticed.

"Our main goal has been to identify the nesting materials that may pose significant risks to terrestrial bird species and pinpoint their origins, in order to develop effective strategies to mitigate these risks to wildlife."

While the use of human-derived materials in bird nests is well known, previous studies have mainly focused on quantifying their prevalence rather than their direct impacts, such as entanglement deaths.

This is the first comprehensive survey of nestling entanglements in a terrestrial bird species to systematically monitor nests from hatching of the eggs to fledging of the birds, to detect early entanglements and provide more accurate entanglement and mortality rates.

Co-author Dr. Inês Catry from the University of Lisbon added, "White storks are known to incorporate discarded human-made materials into their nests, frequently nest near or within human settlements and often forage on organic waste at landfill sites.

"The reasons for using these materials in nest-building are not fully understood, but may relate to their availability and the scarcity of natural ones, while some might also be mistaken for food, being inadvertently incorporated in the nests.

"This study highlights that plastic pollution in terrestrial environments needs to be addressed and solutions to replace or safely discard of hazardous materials are urgently needed."

In this study, the researchers monitored and photographed 32 white stork colonies and 568 nests in Alentejo and the Algarve, southern Portugal, over four years.

They aimed to quantify the amount and types of potentially hazardous anthropogenic nest materials and their impact on nestling mortality. They also analyzed the habitat characteristics and proximity to landfill sites to determine the sources of the materials.

In 2023, they also monitored 93 nests weekly from hatching to fledging to identify vulnerable developmental stages and high-risk materials. Accessing nests where possible with a ladder, they freed the nestlings and removed the materials that had caused the entanglements.

The team found that in 63% of cases, entanglements were caused by ropes, affecting 22 nestlings. The number per nest was highly variable, with some nests having up to 22 ropes. Baler wrap, plastic mesh used to cover hay bales, was found in 13% of nests and caused six nestling entanglements.