Mercury in Little Brown Bat (Myotis lucifugus) Maternity Colonies and Its Correlation with Freshwater Acidity in Nova Scotia, Canada

Abstract

Insectivorous little brown bats are exposed to elevated concentrations of mercury (Hg) through their preference for aquatic-based prey. Here we investigated spatial patterns of total Hg (THg) in fur from 10 little brown bat maternity colonies across Nova Scotia, and assessed relationships with the acidity of nearby lakes and rivers. Total Hg concentrations were measured in fur samples from 149 adult female little brown bats. Values showed significant variation among colonies (mean range 3.76-27.38 μg/g, dry weight), and 48% of individuals had Hg concentrations in excess of the 10 μg/g threshold associated with neurochemical changes in Chiroptera conspecifics (n = 26) from Virginia. Average surface water acidity parameters (pH and acid neutralization capacity) within an 8 km radius of each maternity roost showed strong negative associations with average colony fur THg concentrations. This suggests that freshwater acidity in foraging grounds explains much of the variation in average fur THg concentrations in little brown bat colonies. These findings highlight the significant role that water quality may have on Hg bioaccumulation within terrestrial species that feed on aquatic prey.

Mercury contamination in bats from the central United States

“…The concentrations of Hg in fur observed in the present study all fell within the previously reported ranges for their respective species, although the bats collected in the present study often had lower maximum values than have been reported previously . For a given species, we may have observed lower maximum values in the present study because none of our study sites are located near point sources, as was the case in previous studies .…”

“…The concentrations of Hg in fur reflect the Hg concentrations in bat diets at the time that the hair was grown, usually during late summer/early autumn before migration begins . The concentration of Hg in fur can also be influenced by local point sources of contamination and has even been shown to vary in resident bats at sites relatively close to one another (e.g., between sites in Nova Scotia ). In the present study, the concentration of Hg in the fur of migrant bats likely reflects the Hg contamination at sites across the central United States, and the presence of migrants from a few Hg hotspots could explain the wide range of Hg concentration values we observed within a single species in the present study.…”

“…Several recent studies have identified elevated concentrations of Hg in the tissues of insectivorous bats living near point sources of Hg discharge and in bats far from known point sources of Hg pollution . Prior studies of Hg contamination in bats from North America have focused on sites in the eastern United States and southeastern Canada while other regions of North America have not yet been assessed. Additional studies are needed to assess Hg concentrations in bats from other regions of North America.…”

A national level assessment of metal contamination in bats

“…Kidneys, therefore, represent a valuable indicator for exposure of bats to non-essential metals (Cooke, 2011;Ma, 2011). Fur can represent a valuable less-invasive proxy for endogenous metals contamination monitoring (Hernout et al, 2016;Little et al, 2015), although cautious interpretation is during the time of formation of the fur. Therefore, the moulting cycle is an important factor to consider (Fraser et al, 2013).…”

“…However, such studies are lacking on a larger scale. A recent study has shown associations between freshwater acidity and mercury concentrations contained in bat fur (Little et al, 2015), and such studies on a larger scale are therefore to be encouraged.…”