Dataset for the manuscript Litter availability shapes nest attachment behaviour in open cup-nesting birds

Nest architecture is an important component of avian reproductive behaviour, yet variation in how nests are mechanically attached to supporting vegetation remains poorly documented, particularly in human-modified landscapes. Many birds use flexible natural materials to stabilise open cup nests, but anthropogenic materials may increasingly function as structural “tying” elements where they are locally available. We examined the use of plastic string to attach open cup nests to shrub and tree branches by Red-backed Shrikes (Lanius collurio) across three agricultural landscape types in Poland during the 2021 breeding season (May–August). We monitored 112 nests from egg laying to fledging and recorded anthropogenic litter within 20 m of each nest. Nests were collected after fledging or failure for inspection. String-mediated attachment was common and strongly tracked local availability of strings/litter near nests. Both litter occurrence and attachment frequency varied markedly among landscape types, being highest in intensive arable fields and lowest in meadows and mixed-crop mosaics. In contrast, nest attachment was not associated with laying date or clutch size, and the study period was characterised by broadly similar weather conditions among sites. These findings suggest that open cup-nesting birds can plastically exploit readily available anthropogenic strings as a functional structural component to reinforce nest attachment, linking nest-building behaviour to land-use structure and litter distribution in agricultural environments.