Barn owl feathers as biomonitors of mercury: sources of variation in sampling procedures
Given their central role in mercury (Hg) excretion and suitability as reservoirs, bird feathers are useful Hg biomonitors. Nevertheless, the interpretation of Hg concentrations is still questioned as a result of a poor knowledge of feather physiology and mechanisms affecting Hg deposition. Given the constraints of feather availability to ecotoxicological studies, we tested the effect of intra-individual differences in Hg concentrations according to feather type (body vs. flight feathers), position in the wing and size (mass and length) in order to understand how these factors could affect Hg estimates. We measured Hg concentration of 154 feathers from 28 un-moulted barn owls (Tyto alba), collected dead on roadsides. Median Hg concentration was 0.45 (0.076–4.5) mg kg−1 in body feathers, 0.44 (0.040–4.9) mg kg−1 in primary and 0.60 (0.042–4.7) mg kg−1 in secondary feathers, and we found a poor effect of feather type on intra-individual Hg levels. We also found a negative effect of wing feather mass on Hg concentration but not of feather length and of its position in the wing. We hypothesize that differences in feather growth rate may be the main driver of between-feather differences in Hg concentrations, which can have implications in the interpretation of Hg concentrations in feathers. Finally, we recommend that, whenever possible, several feathers from the same individual should be analysed. The five innermost primaries have lowest mean deviations to both between-feather and intra-individual mean Hg concentration and thus should be selected under restrictive sampling scenarios.
KeywordsBiomonitor Barn Owl Mercury Feathers Intra-individual variations
IR was supported by a doctoral Grant (SFRH/BD/72163/2010), and RL and JPC by post-doctoral degree Grants (BPD/78241/2011 and BPD/102870/2014, respectively) from Fundação para a Ciência e a Tecnologia—Portugal. Fieldwork was partly supported by QREN/INALENTEJO 2007–2013 under the project ECOMEDBIRDS (ALENT-04-0331-FEDER000205) and by Companhia das Lezírias, S.A. through a Business & Biodiversity Protocol with the University of Évora, under the project TYTOTAGUS.
Compliance with ethical standards
Conflict of interest
The authors have no known conflicts of interest associated with this publication and there has been no financial support for this work that could have influenced its outcome.
Human and animal rights
All samples were obtained under the permits of Instituto da Conservação da Natureza e das Florestas (Portugal) numbers: 40, 204-205, 265/2009/CAPT; 165-166/2010/CAPT and 258-260/2012/CAPT (IR, RL and AM). All applicable international, national, and/or institutional guidelines for care and use of animals were followed.
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