Origin of Sulfur in Diet Drives Spatial and Temporal Mercury Trends in Seabird Eggs From Pacific Canada 1968–2015

Mercury (Hg) is a neurotoxin that can be particularly harmful to top predators because it biomagnifies through the food web. Due to variation in the food web structure, variation in Hg exposure in predators may represent variation in diet rather than Hg availability. We measured Hg in eggs from six seabird species (<i>N</i> = 537) over 47 years. In contrast to expectation, storm-petrels feeding partially on invertebrates had the highest Hg burden while herons feeding on large fish had the lowest Hg burden. A multiple regression showed that Hg correlated with δ³⁴S (<i>R</i>² = 0.86) rather than trophic level (δ¹⁵N of “trophic” amino acids). Sulfate-rich environments (high δ³⁴S) have sulfate-reducing bacteria that produce methylmercury. Variation in Hg within and among seabirds near the top of the food web was associated with variation in δ³⁴S at the base of the food web more so than trophic position within the food web. Hg levels in seabirds only changed over time for those species where δ³⁴S also varied in tandem; after accounting for diet (δ³⁴S), there was no variation in Hg levels. Variation in Hg in seabirds across space and time was associated with the origin of sulfur in the diet

Counts and flushing of Thick-billed murres

Sheets 1: Thick-billed murres counts in various plots at Digges Island (with UAV and with ground camera). NA indicate days when we could not count murres in a plot due to various reasons. ///// Sheets 2: Thick-billed murre flushing pourcentage in a plot in reaction to an approaching drone at Coats Island. See the related article for details

Difference between lipid-extracted and non-extracted stable isotope ratios for bird egg tissue.

<p>Specifically (A) carbon (Δδ¹³C), (B) nitrogen (Δδ¹⁵N) and (C) sulphur (Δδ³⁴S) increases with ratio of carbon to nitrogen by weight (C∶N ratio) across seven aquatic bird species: ancient murrelet (ANMU), double-crested cormorant (DCCO), great blue heron (GBHE), Leach's storm-petrel (LESP), osprey (OSPR), pelagic cormorant (PECO) and rhinoceros auklet (RHAU). Also shown are results from studies listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0083597#pone-0083597-t001" target="_blank">Table 1</a> (eider average with SD bars shown, Arctic birds) and best-fit habitat- and species-dependent regression models listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0083597#pone-0083597-t002" target="_blank">Table 2</a>. (D) Δδ¹³C for groups within our study compared with arithmetic lipid-correction models proposed by Post et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0083597#pone.0083597-Bodin1" target="_blank">[29]</a>, Ehrich et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0083597#pone.0083597-Kiljunen1" target="_blank">[33]</a> (filled lines) and within our own study (dashed lines).</p

Difference between lipid-extracted and non-extracted samples for bird egg tissue for carbon (Δδ¹³C), nitrogen (Δδ¹⁵N) and sulphur (Δδ³⁴S).

<p>Difference between lipid-extracted and non-extracted samples for bird egg tissue for carbon (Δδ¹³C), nitrogen (Δδ¹⁵N) and sulphur (Δδ³⁴S).</p

Ranking of models used to describe the difference between lipid-extracted and non-extracted bird egg tissue.

<p>Ranking of models used to describe the difference between lipid-extracted and non-extracted bird egg tissue.</p

Supplementary Methods from Fear creates an Allee effect: experimental evidence from seasonal populations

Detailed method

Frequency of fasting duration at the time of measurements of incubation metabolic rate in ancient murrlets at Reef Island in 2010.

<p>Frequency of fasting duration at the time of measurements of incubation metabolic rate in ancient murrlets at Reef Island in 2010.</p

Baseline CORT levels (ng mL⁻¹) of 38 ancient murrelets by number of chicks that departed to sea.

<p>All samples were taken at the end of incubation period at Reef Island in 2008.</p

The relationships between RQ and the length of fasting endurance, and CORT levels and reproductive success in ancient murrelets.

<p>The relationships between RQ and the length of fasting endurance, and CORT levels and reproductive success in ancient murrelets.</p

DEE calculations

Excel spreadsheet shows raw ppm values from blood samples used for measurement of energy expenditure using doubly-labelled water and equations used to convert those ppm values into energy expenditure. Also shown are calculated PDBA (partial dynamic body acceleration) values relative to measured energy expenditure. The "ID" is the band number that can be cross-referenced with the activity/accelerationd data