Impaired Reproductive Performance of Waterbirds in Metal-Contaminated Tropical Rice Agroecosystems: Evidence from Little Egrets ().

Heavy metal pollution in rice fields is a major concern; however, little research has addressed its exposure and risk to waterbirds inhabiting rice fields. We investigated the accumulation of heavy metals (Cd, Pb, As, Cr, Cu, and Zn) in sediment, water, food, feces, feathers, and eggshell samples collected from different nesting sites (Chongwei Village and Wuji Village) of little egrets () on Hainan Island, China, and compared the differences in their breeding parameters and eggshell quality. Higher levels of heavy metals were observed in all samples except feces from Wuji Village compared to those from Chongwei Village. As, Cd, and Pb exhibited little bioaccumulation in all feather and eggshell samples, whereas Cr concentrations in feather samples from both heronries and eggshell samples in Wuji Village exceeded the toxicity threshold in birds, indicating that the high maternal Cr was transferred to eggs in Wuji Village. Significantly lower hatching and breeding success rates were observed in Wuji Village than in Chongwei Village, which may be closely related to Cr contamination. This study revealed that waterbirds breeding in rice fields are under threat from heavy metal contamination and highlighted the suitability of bird feathers and eggshells as biomonitors of the environment.