Relating trophic ecology and Hg species contamination in a resident opportunistic seabird of the Bay of Biscay.

Methylmercury (MeHg) is the most bioavailable and toxic form of the globally distributed pollutant Hg. Organisms of higher trophic levels living in aquatic ecosystems have potentially higher concentrations of MeHg. In this work, we analysed both MeHg and inorganic Mercury (Hg(II)) concentrations from dorsal feathers of chicks from ten colonies of Yellow-legged Gull (Larus michahellis) in the south-eastern part of the Bay of Biscay. Overall, we detected a high mean MeHg concentration that, however, differed among colonies. Additionally, based on stable isotopes analysis (δ13C and δ15N) and conducting General Linear Mixed Models, we found that chicks which were mostly/mainly fed with prey of marine origin had higher levels of MeHg. We propose Yellow-legged Gull as a reliable biomonitor for Hg species, as it is easy for sampling and in compliance with the Minamata convention on Mercury.

Heavy metal concentration in feathers of Little Egret (Egretta garzetta) nestlings in three coastal breeding colonies in Spain.

The colonial ardeid Little Egret (Egretta garzetta), which is is protected under the European Birds Directive (2009/147/EC), can be a reliable bioindicator of aquatic environmental pollution. Concentrations of the heavy metals Cd, Cr, Cu, Hg, Ni, Pb and Zn in nestling feathers were assessed for three different breeding colonies of Little Egret on the Spanish coast during 2013 (5 individuals in Urdaibai, 10 in Santoña and 26 in Odiel). There were no significant differences in mean tissue residues of Cd, Ni, Pb and Zn between the colonies; however, mean concentration of Hg in Odiel nestlings was approximately three times lower than that of the other colonies, while Cr and Cu were significantly higher. In general, Little Egret nestlings from the three study sites had low levels of most of the measured metals, and thus the breeding populations did not appear to be at risk from heavy metal pollution. Baseline metal concentration in feathers derived from this study and calculated as the 90th percentile values were: 0.02 µg Cd g(−1) dw, 0.42 µg Cr g(−1) dw, 1.63 µg Hg g(−1) dw, 0.40 µg Pb g(−1) dw and 122 µg Zn g(−1) dw. However, mean Cu residues attained relatively high levels (17.6­26.9 µg Cu g(−1) dw) compared with data reported elsewhere, which raises concern and indicates a need for further research.