Declining kingfisher assemblages in the face of hazardous metal pollution in tropical wetlands

Objective: Heavy metals are among the potent toxic contaminants that have become a growing global concern. Discharged from anthropogenic activities, these pollutants persist in aquatic environments due to surface runoff and direct industrial effluent disposal. Heavy metal exposure poses significant health risks, primarily to aquatic organisms, and subsequently to their predators, such as birds, that rely on aquatic prey within food webs. Kingfishers are wetlandassociated birds that play a crucial role in maintaining ecological balance and serve as vital indicators of aquatic ecosystem health. Being top predators in their food chain, they are particularly vulnerable to heavy metal bioaccumulation through their prey. The present study aims to investigate the presence of heavy metals in the droppings of the kingfishers. Method: This study quantified four heavy metals, cadmium (Cd), chromium (Cr), lead (Pb), and arsenic (As), in the droppings of five kingfisher species–Common Kingfisher, Pied Kingfisher, White-throated Kingfisher, Black-capped Kingfisher, Stork-billed Kingfisher–collected from selected study sites: Kadalundi-Vallikkunnu Community Reserve, Kallampara mangroves and Vazhakkad agro-ecosystem, during November, December and January between 2023 and 2024. The samples were analysed using a Flame Atomic Absorption Spectrophotometer. Result: We observed significant variations in metal concentrations among different kingfisher species. White-throated Kingfishers exhibited the highest levels of Cd, Cr, and Pb (60 mg/kg), whereas Black-capped Kingfishers had the lowest concentrations (30 mg/kg). The results revealed a negative correlation between kingfisher abundance and the concentrations of these four hazardous metals, highlighting serious concerns regarding the health and sustainability of kingfisher populations in contaminated environments. Conclusion: These findings indicate that heavy metal toxicity may significantly impact kingfisher populations, contributing to their decline in areas with high contamination levels. With increasing human pressures on aquatic ecosystems, protecting these species will necessitate collaborative efforts focused on habitat preservation and pollution control.