Metal contamination in migratory waterbirds along the East Asian-Australasian flyway: Evidence from a critical wetland stopover site on the Yunnan-Guizhou Plateau

Wetland ecosystems on the Yunnan-Guizhou Plateau constitute critical wintering and stopover habitats for migratory waterbirds along major Asian flyways, yet they are increasingly exposed to environmental pollution pressures. In this study, we quantified concentrations of arsenic (As), lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) in 141 naturally molted feather samples collected from three waterbird species-Ruddy Shelduck (Tadorna ferruginea, n = 94), Eurasian Moorhen (Gallinula chloropus, n = 25), and Little Egret (Egretta garzetta, n = 22)-as well as in 30 sediment samples from a Ramsar-listed plateau wetland in southwestern China. Across all species, feather metal concentrations followed the order Zn > Cu > As > Pb > Cd, with Eurasian Moorhen exhibiting consistently higher burdens of most elements. Despite its low environmental abundance, arsenic displayed the highest bioaccumulation factors, indicating a disproportionate accumulation potential and suggesting that As may represent a priority pollutant in plateau wetland ecosystems. Redundancy analysis revealed that sediment Zn and Cu were the dominant drivers of corresponding feather concentrations, whereas As accumulation showed distinct, species-specific patterns. Feather metal concentrations were positively correlated with body weight, highlighting the role of biological traits in modulating contaminant exposure. Although overall metal levels generally remained within low to moderate ranges, the widespread presence of toxic elements such as As, Pb, and Cd underscores potential ecological risks to waterbirds and reflects ongoing anthropogenic pollution pressures in this internationally important wetland. Our findings demonstrate the value of waterbirds as effective bioindicators and provide critical evidence to support pollution monitoring and management in high-altitude wetlands along migratory flyways.