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Older Female Blackbirds Used More Human-Made Items in Their Nests

Female Eurasian Blackbird
Research: Ecology, Behaviour

Older female Eurasian Blackbirds (Turdus merula) used more human-made items in their nests in an urban population in Szczecin, north-western Poland. The number of artificial items also increased in nests where the first egg was laid later in the season. Human-made material was common, but contributed only a small proportion of total nest mass and was most often placed in the nest base.

The study used nests collected between 2014 and 2021 from a long-term monitored population in Stefan Żeromski Park in central Szczecin. Most birds in this population are individually colour-ringed, allowing the researchers to connect nest composition with the age and breeding history of identified females.

81 nests represented 88 breeding attempts

The researchers examined 81 nests associated with 88 breeding attempts by 44 females. Sixty-one nests could be separated into lining, cup and base, allowing the distribution of natural and human-made materials within the nest structure to be examined. Nearly all artificial items were strip-shaped, and the base was the part of the nest where such material occurred most frequently.

The number of human-made items increased with female age. It also increased with the date of the first egg, meaning later breeding attempts tended to contain more artificial material. Because the study was observational, those relationships do not establish whether age itself changes material preference or whether experienced females encounter, select or use available materials differently.

Successful nests contained more artificial items

Among the 88 breeding attempts, 30 were successful, while other clutches were lost at the egg or chick stage or were abandoned. Nests from successful attempts contained more human-made items than nests where breeding failed.

That association is not evidence that plastic, strings or other artificial materials improved breeding success. Human-made material can have very different effects depending on its form and context: it may alter nest structure or deter some parasites, but debris can also entangle birds, reduce camouflage or expose them to harmful substances. The study discusses several such possibilities without identifying one causal explanation for the pattern seen in these Blackbirds.

Urban nests record both behaviour and material availability

Blackbird nests are built mainly by females from materials collected in the surrounding environment. In cities, the available material pool includes plastics, synthetic strings and other human-made debris alongside twigs, roots, grass, leaves and mud.

The Szczecin results show that incorporation of those materials is not simply a yes-or-no response to living in a city. It varied with the female’s age, breeding date and breeding outcome. Determining whether these patterns reflect experience, local availability, nest function or other behavioural differences will require further tests, but the nests themselves provide a record of how an urban bird interacts with an increasingly human-modified material environment.

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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