First Retrospective Study of Avian Mercury Exposure in a Tropical ASGM Hotspot

Artisanal and small-scale gold mining (ASGM) is the largest anthropogenic source of mercury globally. Few studies have explored how this toxicant affects avian wildlife in Indonesia, an ASGM hotspot. Here, we use feather samples from museum specimens (n = 92) of Indonesian birds to examine changes through time in methylmercury (MeHg), diet, and foraging habitat (inferred from stable isotope ratios of nitrogen, δ¹⁵N, and carbon, δ¹³C, respectively). We ask how MeHg changes between time period (1860-1980 vs. 1980-2019) given increases in mercury emissions due to ASGM and describe how foraging guild and among-species variation in diet influence Indonesian bird feather MeHg concentrations. Time period was not a significant factor, with specimens associated with increased ASGM activity (collected post-1980) not significantly higher in MeHg concentrations compared to specimens collected pre-1980. Feather MeHg concentrations varied significantly among species, foraging guilds, and by habitat use. Carnivore and insectivore MeHg concentrations were above thresholds associated with sublethal effects. This is the first report of MeHg in Indonesian passerines, kingfishers, and woodpeckers. It provides critical information on mercury exposure in a region with high avian diversity that is severely impacted by mercury pollution.