Quantifying variation in δ 13C and δ 15N isotopes within and between feathers and individuals: Is one sample enough?

Abstract

Studies of avian migration increasingly use stable isotope analysis to provide vital trophic and spatial markers. However, when interpreting differences in stable isotope values of feathers, many studies are forced to make assumptions about the timing of moult. A fundamental question remains about the consistency of these values within and between feathers from the same individual. In this study, we examine variation in carbon and nitrogen isotopes by sub-sampling feathers collected from the wings of adults of two small congeneric petrel species, the broad-billed Pachyptila vittata and Antarctic prion P. desolata. Broad-billed prion feather vane material was enriched in 15N compared to feather rachis material, but there was no detectable difference in δ13C. Comparison of multiple samples taken from Antarctic prion feathers indicated subtle difference in isotopes; rachis material was enriched in 13C compared to vane material, and there were differences along the length of the feather, with samples from the middle and tip of the feather depleted in 15N compared to those from the base. While the greatest proportion of model variance was explained by differences between feathers and individuals, the magnitude of these within-feather differences was up to 0.5 ‰ in δ15N and 0.8 ‰ in δ13C. We discuss the potential drivers of these differences, linking isotopic variation to individual-level dietary differences, movement patterns and temporal dietary shifts. A novel result is that within-feather differences in δ13C may be attributed to differences in keratin structure within feathers, suggesting further work is required to understand the role of different amino acids. Our results highlight the importance of multiple sampling regimes that consider both within- and between-feather variation in studies using stable isotopes. Electronic supplementary materialThe online version of this article (doi:10.1007/s00227-015-2618-8) contains supplementary material, which is available to authorized users.

Stable isotope analyses as a forensic tool to monitor illegally traded African grey parrots

“…d 2 H values differ with distance from the coast (Hobson, Michener & Lajtha, 2007) and d 13 C and d 2 H with increased aridity (Rubenstein & Hobson, 2004;Neto, Newton & Gosler, 2006;Hobson, Møller & Wilgenburg, 2013) and anthropogenic change (Hobson, 2007;Hobson et al, 2013), resulting in possible isotope differences between the African grey parrots from the more forested and mesic central Africa and from the xeric and agriculturally transformed western and eastern regions (Mayaux, 2004; Hobson et al, 2013). Often illegally caught African grey parrots are subjected to stressful and nutrient-deficient conditions, resulting in variable isotope values, as observed in several captive and wild bird studies (Hobson & Clark, 1992b;Bearhop, Waldron & Votier, 2002;Fox, Hobson & Kahlert, 2009;Grecian, McGill & Phillips, 2012), where body stores are utilized to recover from nutrient deficient situations. The variability in d 13 C and d 2 H isotope values in the unknown and captive feathers was greater than the wild samples, and likely a result of differences in diet.…”

“…It was suggested that primary feathers of bullfinches Pyrrhula pyrrhula and greenfinches Carduelis chloris grow slower than both body and tail feathers (Newton, 1967) and thus assimilate nutrients at different rates; this may also apply to African grey parrots. An alternative explanation could be the routing of d 13 C and d 15 N to different tissues or from different body pools for different tissues/feather types (Gannes et al, 1997;Bearhop et al, 2002;Ayliffe et al, 2004;Dalerum & Angerbjӧrn, 2005;Fox et al, 2009;Grecian et al, 2012;Storm-Suke, Norris & Wassenaar, 2012).…”

Are stable isotope ratios and oscillations consistent in all baleen plates along the filtering apparatus? Validation of an increasingly used methodology

“…Validation and standardization of the sampling of archival tissues to infer ecological and physiological traits, variation in diet or migration have been conducted in a number of species and for a variety of keratinous structures, such as human and other animal hair, pinniped vibrissae or bird feathers . These studies have involved assessment of variability within individuals and within repeated samples of the same individual.…”

Age, growth and population structure of invasive lionfish (Pterois volitans/miles) in northeast Florida using a length-based, age-structured population model

“…Gardner et al (2015) reported two peak spawning periods for lionfish in the Cayman Islands occurring in spring and late summer, and spawning activity also peaks in summer in the eastern Gulf of Mexico (Fogg, Brown-Peterson & Peterson, 2013), North Carolina and The Bahamas (Morris Jr, 2009). Source populations for larvae settling in northeast Florida are not definitively known, but evidence from population genetics (Freshwater et al, 2009; Butterfield et al, 2015), biophysical modeling (Cowen, Paris & Srinivasan, 2006; Johnston & Purkis, 2011; Johnston & Purkis, 2015) and chronology of invasion history (Schofield, 2009) suggest a combination of self-recruitment and subsidies from upstream locations such as southern Florida and northern Cuba. Unfortunately, little is known about reproductive biology of lionfish in these regions.…”