A paired analysis of mercury among non-invasive tissues to inform bat conservation monitoring

Contaminant exposure can harm wildlife. However, measuring contaminant exposure in wildlife can be challenging due to accessibility of species and/or sampling tissue matrices needed to answer research questions regarding exposure. For example, in bats and other taxa that roost, it may be best to collect pooled feces from colonies for minimal disturbance to species of conservation concern, but fecal contaminant concentrations do not provide contaminant bioaccumulation estimates. Thus, there is a need for quantifying relationships between sample matrices for measuring contaminant exposure to answer research questions pertaining to wildlife health and addressing conservation needs. Our goal was to determine relationships between fecal and fur total mercury (THg). To do so, we collected paired feces and fur from Mexican free-tailed bats (Tadarida brasiliensis) in summer 2023 in western Oklahoma at a maternity roost with no known Hg point source. We analyzed THg in each sample matrix for each individual (n = 48). We found no relationship between individual fecal and fur THg. However, when averaged, fur THg was 6.11 times greater than fecal THg. This factor can be used as a screening-level risk assessment of under-roost feces, which could then be followed by direct assessments of fur THg concentrations and health impacts. We encourage the use of this conversion factor across other insectivorous bat species and sites for estimating initial risks of contaminant exposure with minimal disturbance to species of conservation concern, when timely research for conservation actions are needed, and when a contaminant point source is not yet known. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=103 SRC="FIGDIR/small/587502v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@4bac41org.highwire.dtl.DTLVardef@1a13deorg.highwire.dtl.DTLVardef@e8e58org.highwire.dtl.DTLVardef@1a33a9d_HPS_FORMAT_FIGEXP M_FIG C_FIG Graphical abstract created in BioRender under a free subscription. Cave icon created by artist Freepik at https://www.flaticon.com/free-icons/cave. HighlightsO_LIUnder-roost sampling for contaminant exposure minimizes species disturbance C_LIO_LIContaminant exposure relationships in tissues can aide in measuring wildlife health C_LIO_LIWe sampled Tadarida brasilliensis for paired fecal and fur total Hg (THg) C_LIO_LITHg in fur averaged 6.11 times greater than feces C_LIO_LIThis factor can be used as an initial risk assessment for under-roost fecal sampling C_LIO_LIMore invasive follow-up sampling (bat fur) can be justified following risk assessment C_LI