Seasonal mercury in an endangered primate from fragmented karst forest: Does behavioral observation advance...

Pollution may drive local extinctions, particularly among threatened species, yet ecological risk assessments seldom incorporate animal behavior-potentially underestimating risks for behaviorally flexible species. Using year-round, individual-level behavioral data, we assessed mercury (Hg) exposure and ecological risk in the critically endangered White-headed Langur (Trachypithecus leucocephalus), which inhabits fragmented karst forests in Southwest China. Langurs spent approximately 90 % of their foraging time along forest edges near agricultural areas, where Hg exposure was elevated due to the consumption of preferred young leaves, with Hg concentrations often exceeding national food safety standards. Specifically, 66 % of sampled plants surpassed the Chinese threshold for vegetables (10 µg/kg), in some cases by up to threefold. During the dry season, when natural food was scarce, langurs expanded their diet and increased foraging near agricultural zones by 8.4 %, further intensifying their exposure risk. Mercury concentrations in both food plants and fecal samples were significantly higher during this period. Overall, the population faces notable ecological risks from Hg exposure, with lactating females being particularly vulnerable during the dry season. Our findings demonstrate that adaptive foraging behavior strongly influences Hg intake, underscoring the need to integrate behavioral ecology into ecotoxicological assessments to better inform effective conservation and management strategies.