Validating quantitative fatty acid signature analysis to estimate diets of spectacled and Steller’s eiders (Somateria fischeri and Polysticta stelleri)

Abstract

Fatty acid (FA) signature analysis has been used to study foraging ecology and food webs in marine ecosystems. This powerful method provides information about diets over an extended time period (e.g., 2-4 weeks), rather than just the most recent meal as with most traditional approaches. Using consumer FA signatures, along with a comprehensive database of diet FA signatures, and accounting for consumer FA metabolism, it is possible to estimate the proportions of diet items in the consumer's diet using quantitative FA signature analysis (QFASA). However, before applying QFASA to free-ranging populations, ideally, controlled feeding studies are performed to determine FA deposition and turnover characteristics. We conducted feeding experiments to validate QFASA in captive spectacled eiders (Somateria fischeri) and Steller's eiders (Polysticta stelleri) as a minimally invasive method for studying the diets of these threatened species. We determined FA deposition in eider adipose tissue relative to long-term diet, and developed calibration coefficients (CCs) to account for eider lipid metabolism. Using these CCs with subsequent diet trials, QFASA accurately indicated diet and diet switches. QFASA estimates also indicated that turnover of dietary FAs was not complete by 21 or 29 days, and confirmed that diets could be estimated over an extended period of >29 days. Thus, our understanding of diet can be backtracked to more than a month in captive feeding eiders. We conclude that applying QFASA techniques to eiders and other birds in the wild has the potential to provide valuable information about their diets at various life history stages.

From lavage to lipids: estimating diets of seabirds

“…CCs are determined from captive validation studies in which a predator consumes a single diet over a period long enough for complete FA turnover, assuming then that the FA signature of the predator's lipid stores will resemble the diet FA signature as much as possible and any differences can be attributed to metabolic processing of individual FAs. To date, seabird adipose tissue CCs have been estimated in chicks of common murres and tufted puffins Fratercula cirrhata and in adults of Steller's eiders Polysticta stelleri, spectacled eiders Somateria fischeri and yellowlegged gulls Larus michahellis , Williams et al 2009, Wang et al 2010, Käkelä et al 2010. Although the CCs estimated from the various studies share many similarities (including some similarities with CCs determined for marine mammals; Iverson 2009), it is not yet known whether differences are due to species, age (adult versus chick), feeding regime, and/or study effects.…”

“…Secondly, a better understanding is needed of the time frames of FA turnover in fat stores and thus the time frame of dietary history they represent. Several controlled studies have been conducted that begin to address this in seabirds (Williams et al 2009, Wang et al 2010. However, how these time fames differ during periods of fat storage versus high-energy use is not known.…”

Carbon isotopic fractionation in eider adipose tissue varies with fatty acid structure: implications for trophic studies

“…Adipose tissues were collected from all birds at the end of the 180days. A biopsy technique was used to obtain approximately 0.1g of synsacral adipose tissue samples from individuals via a 1cm skin incision Wang et al, 2010). The area was disinfected prior to biopsy with a betadine swab and lidocaine spray.…”

“…It may also be possible to combine information from proportional FA composition (e.g. Iverson et al, 2004;Wang et al, 2010) with d…”

“…New techniques using minimally invasive sampling methods and biochemical signatures in stored fat Wang et al, 2010), blood (Käkelä et al, 2009;Federer et al, 2010), stomach oil (Connan et al, 2005;Wang et al, 2007), feathers (Hobson and Clark, 1992) or eggs (Hobson, 1995;DeVink et al, 2011) provide promising alternatives for diet assessments in avian populations. These biomarker techniques typically involve either stable isotope or fatty acid (FA) analysis.…”