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Food stress, but not experimental exposure to mercury, affects songbird preen oil composition


Mercury is a global pollutant and potent neurotoxic metal. Its most toxic and bioavailable form, methylmercury, can have both lethal and sublethal effects on wildlife. In birds, methylmercury exposure can disrupt behavior, hormones, the neuroendocrine system, and feather integrity. Lipid-rich tissues and secretions may be particularly susceptible to disruption by lipophilic contaminants such as methylmercury. One such substance is feather preen oil, a waxy secretion of the uropygial gland that serves multiple functions including feather maintenance, anti-parasitic defense, and chemical signaling. If methylmercury exposure alters preen oil composition, it could have cascading effects on feather quality, susceptibility to ectoparasites, and mate choice and other social behaviors. We investigated whether exposure to methylmercury, either alone or in association with other stressors, affects preen oil chemical composition. We used a two-factor design to expose adult song sparrows (Melospiza melodia) to an environmentally relevant dietary dose of methylmercury and/or to another stressor (unpredictable food supply) for eight weeks. The wax ester composition of preen oil changed significantly over the 8-week experimental period. This change was more pronounced in the unpredictable food treatment, regardless of dietary methylmercury. Contrary to our prediction, we found no main effect of methylmercury exposure on preen oil composition, nor did methylmercury interact with unpredictable food supply in predicting the magnitude of chemical shifts in preen oil. While it remains critical to study sublethal effects of methylmercury on wildlife, our findings suggest that the wax ester composition of preen oil is robust to environmentally relevant doses of this contaminant.

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We thank T. Kelly and R. Whiley for help with mist netting in 2018 and R. Whiley, J. Fu, A. Khaira, J. Kwon, T. Meng, S. Park, and T.H. Woldetensae for assistance with animal care. A. Boyer, M. Brodbeck, N. Carfagnini, C. Carter, G. Casbourn, A. Diez, T. Kelly, and B. Samuels helped with blood sampling. Finally, we thank J. Warner and the Biotron Centre for Climate Change Research Analytical Laboratory for assistance with mercury analyses. We acknowledge that the land on which this research was conducted is located on the traditional territories of the Anishnaabek, Attawanderin, Haudenoshaunee, Huron-Wendat, and Lenape.


This work was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) through Discovery Grants to EAM-S and SAM-S and a Vanier Canada Graduate Scholarship to LAG.

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Correspondence to L. A. Grieves.

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All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All birds were captured under permission from the Canadian Wildlife Service and Environment and Climate Change Canada (Scientific Collection Permit CA 0244; banding subpermits 10691E, F). All animal procedures were approved by The University of Western Ontario Animal Use Subcommittee (protocol #2017-161).

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Grieves, L.A., Bottini, C.L.J., Branfireun, B.A. et al. Food stress, but not experimental exposure to mercury, affects songbird preen oil composition. Ecotoxicology (2020).

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  • Mercury
  • Methylmercury
  • Preen oil
  • Songbird
  • Stress
  • Uropygial gland