Microplastics in guano of three Peruvian guano seabird species at Punta Coles, Humboldt Current System

Microplastics (MPs) are increasingly reported in seabird feces, but fecal deposits of Peruvian guano birds remain unexplored. We quantified MPs in feces of three guano-producing seabirds (Sula variegata, Phalacrocorax bougainvillii, Pelecanus thagus) at Punta Coles, a guano headland within the Reserva Nacional Sistema de Islas, Islotes y Puntas Guaneras (RNSIIPG), Peru. Fecal samples from 67 sampling points were processed by density separation (NaCl, ~1.2 g cm^-3), Fenton oxidation, stereomicroscopy and μ-Raman spectroscopy. MPs were detected in 80.6% of samples (n = 54 particles), with median abundance 0.20 items g^-1 dw (mean 0.16 ± 0.08) and no significant differences between habitat zones (Wild vs. Direct-use; Mann-Whitney U = 534.5, p = 0.985) or among species (Kruskal-Wallis H = 0.772, p = 0.680). Assemblages were dominated by filaments (66.7%), with fragments (29.6%) as secondary contributors and microbeads rare (3.7%). Polyester (PET, 58.0%) was the main polymer, followed by polyamide (PA, 20.0%) and polypropylene (PP, 8.0%); blue and white/grey were the most frequent colours. μ-Raman spectroscopy confirmed 92.6% of analysed particles (50/54). Multivariate analyses (PCA, NMDS, MFA, PERMANOVA) and co-occurrence networks revealed a homogeneous PET-PA-PP filament-dominated assemblage with no detectable compositional differences between zones or species (all R² ≤ 0.16, p > 0.05). Effect sizes were small (r ≤ 0.18, η² ≈ 0), and the detection limit (~40 μm) excluded smaller MPs and nanoplastics. Fecal surveys offer a practical, non-lethal approach to monitor seabird-mediated fluxes of MPs in the Humboldt Current system, with potential applications for long-term surveillance within Peru's marine protected area network.