Human-made material use in urban European Blackbird nests varies with breeding characteristics and female age

Abstract Human activity has profoundly altered the environment, with anthropogenic material pollution posing serious threats to wildlife. In birds, the incorporation of human-made materials into nests may have harmful effects, such as reducing survival and reproductive success, or beneficial effects, including parasite deterrence or social signalling. We investigated the use of human-made materials in the nests of an urban population of European Blackbirds ( Turdus merula ). We found that the use of human-made materials was common. Nearly all incorporated items were strip-shaped, their total mass represented only a small proportion of the nest mass, and they were most frequently located in the nest base. The number of human-made items increased with female age and first-egg laying date. Nests with successful breeding attempts contained more human-made items than nests in which breeding failed. These findings are discussed in the context of several hypotheses that may explain the incorporation of human-made materials into bird nests. They also contribute to our understanding of the ecological and evolutionary significance of human-made material use in nesting.