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Older Female Blackbirds Built More Debris Into Their Nests

Female Eurasian Blackbird
Research: Ecology, Behaviour

Blackbirds do not build only with twigs, roots, grass and mud. In a city park in Szczecin, north-western Poland, researchers also found plastic strips, strings and other human-made materials in their nests. Older females used more such items than younger ones, and the number also increased later in the breeding season.

Female Eurasian Blackbirds (Turdus merula) do most of the nest-building. The study examined 81 nests from 44 females, collected in Stefan Żeromski Park during 2014–2021. Individual colour rings allowed researchers to link nests to particular females, their ages and breeding histories.

Strips and Strings in the Nest Base

Human-made materials were common but contributed only a small proportion of total nest weight. Almost all the items were strip-shaped, and they occurred most often in the nest base, which supports the cup and its inner lining.

The shape of these materials is interesting because birds may select objects that resemble natural building materials. Another possibility is that strings and strips help hold a nest together. The researchers discuss both explanations, but the study does not establish why the Blackbirds used these materials.

The greater number of items used by older females raises questions about experience and changing material choices. Timing also mattered: nests in which the first egg was laid later contained more human-made items.

More Items in Nests That Fledged Young

Nests from successful breeding attempts contained more of these items than nests where breeding failed. Success meant that at least one chick fledged.

This finding does not show that debris helped the young. Materials that could support a nest structure can also be dangerous if birds become entangled in them. The central finding is that female Blackbirds used the city’s available building materials differently, with use varying by both age and timing within the breeding season.

Sources and image credit

  1. Cholewa, M., Witkowska, M., Borawski, P., Fritsch, C., & Wysocki, D. (2026). Human-made material use in urban European Blackbird nests varies with breeding characteristics and female age. Scientific Reports.Primary peer-reviewed Article in Press published 21 September 2026. Full 13-page early article checked. Data from 81 nests representing 88 breeding attempts by 44 females were collected in Stefan Żeromski Park, Szczecin, Poland, during 2014–2021.

Image: Female Eurasian Blackbird (Turdus merula), Edinburgh, Scotland, 17 April 2025. Photo: Marcelpb 12 / Wikimedia Commons. Representative image; not a study bird. · CC BY 4.0 · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

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