Mercury contamination, a potential threat to the globally endangered aquatic warbler Acrocephalus paludicola

Abstract

Mercury (Hg) contamination is considered a global concern for humans and wildlife, and although the number of studies dealing with that issue continues to increase, some taxonomic groups such as small passerine birds are largely understudied. In this paper, concentration of mercury in the aquatic warbler (Acrocephalus paludicola) feathers, a globally threatened passerine species, was examined. The concentration differences between two ages and sexes were investigated. The comparison of feathers taken on autumn migrants of two age categories act as a comparison of the species’ exposure within the two different areas (European breeding or African wintering grounds). The average Hg concentration for all sampled individuals [2.32 μg/g dw (range 0.38–12.76)] is relatively high, compared with values found in other passerine species. An age difference was found, with first-year individuals displaying higher mercury concentrations than adults. This indicates that birds are exposed to mercury pollution during the breeding season, i.e., in the continental floodplains of eastern Europe. The average Hg concentration in feathers grown on the breeding grounds was 3.88 ± 2.59 μg/g dw, closer to the critical value of 5 μg/g dw, which is considered to impair the health of individuals. The findings suggest that mercury pollution may constitute a threat so far neglected for the endangered aquatic warbler.

Global mercury concentrations in biota: their use as a basis for a global biomonitoring framework

“…An increasing number of studies characterizing Hg exposure in songbirds (Passeriformes) are demonstrating that certain clades are at higher risk than others, based largely on foraging behavior, and breeding habitats (Cristol and Evers 2020 ). Generally, gleaning, flycatching, and “predatory” songbirds that breed in wetland habitats (Edmonds et al 2010 ; Jackson et al 2011a , 2015 , 2020 ; Hartman et al 2013 ; Ackerman et al 2016 ; Pacyna et al 2017 ; Ackerman et al 2019 ), including estuaries (Lane et al 2011 ; Kopec et al 2018 ; Sayers et al 2021 ), rice fields (Abeysinghe et al 2017 ; Xu et al 2024 ) and tropical evergreen forest floodplains (Sayers et al 2023 ) are at highest risk of Hg exposure, especially species that forage on predaceous arthropods such as spiders (Cristol et al 2008 ; Janssen et al 2023 ). The availability of MeHg to tropical resident songbirds (and other landbird groups) is increasingly becoming more evident and are more elevated for certain foraging guilds and habitat types (Lane et al 2013 ; Townsend et al 2013 ).…”

“…Contamination can arise directly from inorganic Hg point sources, such as those along rivers (Jackson et al 2011a ; Kinghorn et al 2007 ; Nguetseng et al 2015 ; Santschi et al 2017 ; Geyer and Ralston 2018 ), around lakes (Anderson et al 2008 ; Suchanek et al 2008 ; Kumari and Maiti 2019 ; Chen et al 2021 ), and in estuaries (Eagles-Smith and Ackerman 2009 ; Chen et al 2014 ; Buckman et al 2015 ; Sullivan and Kopec 2018 ). Owing to atmospheric transport, inorganic Hg sources may not be local (i.e., <100 km) and subsequent impacts to biota are well described in most continents, including North America (Evers and Clair 2005 ; Evers et al 2011a ; Ackerman et al 2016 ; Eagles-Smith et al 2016a , b ; Evers et al 2020 ; AMAP 2021 ), South America (Sebastiano et al 2016 ; May Junior et al 2017 ; Manhães et al 2022 ), Europe (Åkerblom et al 2014 ; Nguetseng et al 2015 ; Pacyna et al 2017 ), Asia (Kim et al 2012 ; Watanuki et al 2016 ; Abeysinghe et al 2017 ; Noh et al 2017 ), Africa (Hanna et al 2015 ; van Rooyen et al 2023 ), and multiple ocean basins (Carravieri et al 2014 , 2016 ; Peterson et al 2015 ; Drevnick et al 2015 ; Lee et al 2016 ; Bodin et al 2017 ; Drevnick and Brooks 2017 ; Chastel et al 2022 ).…”

Mercury toxicity risk and corticosterone levels across the breeding range of the Yellow-breasted Chat

“…Most passerines replace their tail feathers about halfway through their moult beginning with the innermost tail feathers (Pyle 1997 ). Therefore, using tail feathers likely underestimates the true body burden of chat Hg concentrations accumulated since the last moult, but these are common feathers used in analyses and therefore are suitable for comparison (Warner et al 2012 ; Pacyna et al 2017 ; Óvári et al 2018 ). We believe that the strength of our study is that the same methods were employed across all individuals in their range, allowing for suitable relative comparisons of Hg exposure between individuals and populations (Bortolotti 2010 ).…”

“…Recent evidence suggests that songbirds, especially those that use riparian, aquatic, and wetland habitats, may be at risk of Hg exposure through the consumption of carnivorous and aquatic invertebrates (Rimmer et al 2005 ; Brasso and Cristol 2008 ; Edmonds et al 2010 ; Evers et al 2012 ; Jackson et al 2015 ; Ackerman et al 2016 ; Pacyna et al 2017 but see Brasso et al 2020 ). Because Hg biomagnifies, songbirds that consume arthropods at higher trophic levels, including spiders, can accumulate elevated levels of Hg (Rimmer et al 2005 ; Cristol et al 2008 ; Keller et al 2014 ; Li et al 2021 ).…”

Mercury exposure in relation to foraging ecology and its impact on the oxidative status of an endangered seabird

“…Indeed, although the detrimental effects of Hg exposure in captive birds have long been known, we still have a poor understanding of the effects of sublethal Hg concentrations on individual health of free-living birds (Whitney and Cristol, 2017), and their consequences at the population level (Goutte et al, 2014a;Goutte et al, 2014b), particularly in bird species of conservation concern (Pacyna et al, 2017;Tsao et al, 2009). Seabirds are long-lived top predators of marine food webs, bearing high levels of Hg (Rowe, 2008); thus they prove valuable to study the effects of Hg exposure in birds.…”