# Relationship between Hg accumulation and diet in bats from Atlantic forest reserves

## TL;DR

Bats in the Atlantic Forest show mercury levels linked to their diet, with insect-eating bats most affected, suggesting they can help track mercury pollution in ecosystems.

## Contribution

This study demonstrates how bat feeding habits influence mercury accumulation and stable isotope signatures in a tropical forest ecosystem.

## Key findings

- Mercury concentrations varied significantly among bat feeding guilds, with carnivorous bats having the highest levels.
- Insectivorous bats showed higher δ¹⁵N and mercury concentrations, likely due to their diet of invertebrates.
- Twenty-three percent of bats exceeded a mercury threshold linked to neurological effects, highlighting their role as pollution sentinels.

## Abstract

Bats are valuable bioindicators of Hg contamination due to their wide representation across food webs, broad distribution, and high species richness worldwide. This study evaluated the influence of feeding habits and stable isotopes (δ¹³C and δ¹⁵N) on Hg concentrations in bats from a protected forest complex in southeastern Brazil. We collected road-killed bats (n = 100) along a highway crossing protected areas between 2012 and 2017. The mean Hg concentration (5.6 mg/kg; range: <0.003–71.3 mg/kg) found in the present study was higher than values reported for bats from reference sites, comparable to levels observed in the Peruvian Amazon (an area also affected by artisanal small-scale gold mining), and considerably lower than those measured in populations from highly contaminated regions. Hg concentrations did not vary with forearm length or sex but differed among feeding guilds, following the order: carnivorous > insectivorous > omnivorous > nectarivorous > frugivorous. Higher δ¹⁵N values and Hg concentrations observed in insectivorous bats likely reflect their diet of invertebrates, while lower δ¹⁵N values in frugivorous and nectarivorous bats are consistent with primarily plant-based diets. Differences in δ¹³C values among feeding guilds indicate variation in carbon sources and habitat use. In this study, 23% of bats exceeded the sub-clinical threshold of 5 mg/kg, a level associated with potential neurological and neurochemical effects. These findings demonstrate the influence of feeding guilds on δ¹³C, δ¹⁵N, and Hg concentrations in a tropical bat assemblage from the Atlantic Forest, highlighting their potential as sentinels for monitoring Hg contamination. Given their ecological diversity and varied feeding strategies, bats provide valuable insights into Hg sources and pathways within ecosystems. The susceptibility of insectivorous bats underscores the need to prioritize this group in future monitoring programs and conservation strategies, particularly in tropical ecosystems where high bat diversity coincides with intense anthropogenic pressures.

The online version contains supplementary material available at 10.1007/s10646-026-03067-y.