Tracing Human Footprint in Bird Nests: Plastic Occurrence and Drivers in the Long-Legged Buzzard (Buteo rufinus)

Anthropogenic plastic pollution is rapidly becoming embedded in terrestrial ecosystems, yet its long-term persistence in raptor nesting structures and its transfer across species remain largely overlooked. We investigated the occurrence of macroplastic debris (≥ 20 mm) in nests of the Long-legged Buzzard (Buteo rufinus) across its breeding range in Dobrogea, Romania, during the 2025 breeding season. A total of 172 historically recorded nest locations were surveyed, of which 60 were confirmed as actively used by Long-legged Buzzards and 68 were reused by secondary species, while the remainder were unoccupied, degraded, or had disappeared. Macroplastic materials were recorded in 63.93% of Long-legged Buzzard nests, a frequency substantially higher than in nests occupied by Common Kestrels (Falco tinnunculus; 14.89%, n = 46) and Eurasian Magpies (Pica pica; 5.26%, n = 19), differences that were statistically significant (χ ² = 37.49, df = 2, p < 0.001). In all secondary users, plastic debris was confined to the basal nest layer, indicating that materials persisted from original buzzard constructions and were subsequently inherited through interspecific nest reuse. Distance to the nearest settlement was the only statistically significant environmental predictor of plastic abundance (Z = -2.878, p = 0.004, 95% CI: 0.0002-0.001), with nests located closer to human settlements containing significantly higher numbers of plastic items. These findings reveal that raptor nests can function as long-term reservoirs of plastic pollution, enabling multi-seasonal and cross-species exposure within avian communities sharing the same nesting infrastructure. Our study identifies a plausible and previously overlooked pathway through which anthropogenic waste may accumulate and persist in terrestrial ecosystems, with potential consequences for nestling survival through entanglement and exposure to plastic-associated contaminants, underscoring the need to integrate plastic pollution monitoring into raptor conservation frameworks.