Untangling causes of variation in mercury concentration between flight feathers

Abstract

Bird feathers are one of the most widely used animal tissue in mercury biomonitoring, owing to the ease of collection and storage. They are also the principal excretory pathway of mercury in birds. However, limitations in our understanding of the physiology of mercury deposition in feathers has placed doubt on the interpretation of feather mercury concentratoins. Throughout the literature, moult sequence and the depletion of the body mercury pool have been taken to explain patterns such as the decrease in feather mercury from the innermost (P1) to the outermost primary feather (P10) of the wing. However, it has been suggested that this pattern is rather a measurement artefact as a result of the increased feather mass to length ratio along the primaries, resulting in a dilution effect in heavier feathers. Here, we attempt to untangle the causes of variation in feather mercury concentrations by quantifying the mercury concentration as mg of mercury (i) per gram of feather, (ii) per millimetre of feather, and (iii) per day of feather growth in the primary feathers of Bulwer's Petrel Bulweria bulwerii chicks, effectively controlling for some of the axes of variation that may be acting in adults, and monitoring the growth rate of primary feathers in chicks. The mercury concentration in Bulwer's Petrel chicks' primaries increased from the innermost to the outermost primary for all three concentration measures, following the order of feather emergence. These observations confirm that the pattern of mercury concentration across primary feathers is not an artefact of the measure of concentration, but is likely an effect of the order of feather growth, whereby the earlier grown feathers are exposed to higher blood mercury concentrations than are later moulted feathers as a result of blood mercury depletion.

Higher mercury contamination is associated with shorter telomeres in a long-lived seabird – A direct effect or a consequence of among-individual variation in phenotypic quality?

“…In 2017, 2 cm of the tips of the secondary 8 flight feather from both wings were sampled. These specific feathers are postulated to moult or regrow while the birds are in the non-breeding area and after many other flight feathers have already moulted (Ramos et al, 2009), reflecting accumulated mercury birds are exposed to in the non-breeding area (Gatt et al, 2021a). Mercury concentration in homogenised feather samples was quantified by thermal decomposition atomic absorption spectrometry with gold amalgamation using an AMA-254 spectrophotometer (LECO, Czech Republic), as described by Costley et al (2000).…”

“…Telomere length was measured in erythrocytes using high precision telomere restriction fragment analysis (Nussey et al, 2014), which provides information on average telomere length and the intra-individual telomere length distribution within the genome (Bauch et al, 2014;Pineda-Pampliega et al, 2019). Mercury concentration was measured in secondary 8 flight feathers, which is an integrated measure of contamination accumulated over the period of feather growth (Gatt et al, 2021a). Specifically, our aims were to test (1) whether mercury concentration is related to telomere length;…”

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

“…We acknowledge that there have been mixed recommendations on using feathers, especially flight feathers, to draw conclusions about Hg exposure in birds (Bond and Diamond 2008;Peterson et al 2019;Low et al 2020). Hg levels in feathers generally correspond with the order of moult, with the first-moulted feathers containing the highest Hg levels (Furness et al 1986;Bottini et al 2021;Gatt et al 2021). Most passerines replace their tail feathers about halfway through their moult beginning with the innermost tail feathers (Pyle 1997).…”

Monitoring of mercury in the mesopelagic domain of the Pacific and Atlantic oceans using body feathers of Bulwer's petrel as a bioindicator

“…As a result, quantifying mercury in feathers provides temporal and spatial contexts (Hobson, 1999;Monteiro and Furness, 1995). It is known, however, that some mercury is accumulated previous to moult, and the first feathers to be moulted display higher concentrations than the ones moulted later (Gatt et al, 2020a). Avoiding feathers that are moulted earlier (such as the inner primaries) and taking a large number of feathers minimizes and dilutes this problem.…”