Mercury contamination: a hidden threat to long-distance migrant shorebirds in critical wintering sites on the west coast of India

Of the many hypotheses attributed to the global decline in shorebirds, an important one is the exposure to contaminants, particularly to wintering shorebirds. However, there is limited information available on contaminant levels in winter migrant shorebirds, especially within the Central Asian Flyway (CAF). This research gap is addressed in this study on total mercury (THg) contamination in 10 species of long-distance migrant shorebirds along the west coast of India from 2019 to 2021. Of the 10 species studied, the highest concentration of THg was reported in the droppings of Common Redshank in the mangroves (81.29 ± 6.82 mg/kg wet wt) and the lowest was reported in Little Stint in sand beach (17.40 ± 2.14 mg/kg wet wt). The Kadalundi-Vallikunnu Community Reserve (KVCR) and its adjacent sand beaches serve as vital stop-over sites within the CAF, catering to the nutritional needs of various migratory shorebirds, including transoceanic, oversummering, and locally moving species. This research offers solid evidence of THg concentration in predators occupying high trophic levels of the coastal ecosystems in the KVCR and surrounding areas. Understanding the extent and impact of THg concentration on both organisms and their habitat is crucial. The study highlights a significant increase of THg concentration across the years. Additionally, it provides essential information to support extensive, long-term biomonitoring efforts aimed at conserving shorebirds regionally and globally.