Across southern Europe’s farmland, towering stork nests have long stood as signs of life and resilience. Built over decades, these massive structures—some weighing up to a tonne—house not only white storks but also a host of other bird species. Yet, inside these high nests, a silent threat is emerging: plastic.

Recent field research has uncovered alarming patterns of entanglement in white stork chicks, primarily caused by synthetic baler twine—plastic string commonly used in agriculture. In an intensive multi-year study, ecologists systematically photographed and climbed hundreds of nests during the 2023 breeding season. Their goal: to understand the real impact of plastic debris on land-based birds.

The results are stark. About 90% of nearly 600 nests examined contained plastic. Of those nests physically inspected during the breeding season, over one in four had chicks tangled in plastic, most of them only weeks old. These chicks often suffer strangulation, amputations, or lethal infections.

The leading source of entanglement is baler twine or its wrapping, while household plastics like bags and containers played a smaller role. As chicks grow and instinctively move within the nest, plastic cords can cinch tighter around their bodies, turning a safe haven into a trap.

While the dangers of marine plastic pollution are well documented, with many species suffering from ingestion or entanglement, terrestrial birds are facing similar threats that have gone largely unnoticed. Part of the issue is methodological: traditional nest monitoring often occurs too late to capture early chick fatalities. In many cases, dead nestlings are removed by parents before researchers ever arrive.

What sets this study apart is its frequency and depth. Weekly nest inspections allowed for a clearer picture of mortality and its causes, revealing an entanglement rate much higher than previous estimates, which ranged from 0.3% to 5.6% in other regions. The findings raise concerns about the broader impact on bird populations, especially those already vulnerable to habitat loss and climate change.

Plastic baler twine is used extensively across Europe, with tens of thousands of tonnes deployed each year. While some collection and recycling efforts exist, they are inconsistent, and in many areas, plastic is left behind in the fields, where it’s picked up by birds during nest-building. Although biodegradable alternatives are under development and some are available, uptake remains limited.

Conservationists are now calling for stronger action: classifying polypropylene baler twine as a hazardous material and removing it from circulation. They also recommend targeted cleanup efforts in rural landscapes to reduce the existing environmental burden.

The presence of plastic in nests is not isolated to Portugal or storks alone. Reports of similar entanglements are emerging from multiple continents and across a wide range of bird species. As the use of synthetic materials grows and natural habitats shrink, the nesting behaviors that once ensured survival are now becoming a point of vulnerability.

In what were once symbols of renewal and continuity, plastic has quietly woven itself into the fabric of life—and death—at the treetop level.