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 δ 13C. 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 δ 15N and 0.8 ‰ in δ 13C. 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 δ 13C 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.
Highlights
Stable isotope analysis has provided the study of avian migration with vital trophic and spatial markers (Hobson 1999; Newsome et al 2007; Inger and Bearhop 2008)
We examined isotopic variation in feathers collected from adults of two small congeneric petrel species, the broad-billed prion Pachyptila vittata and Antarctic prion P. desolata
Differences between samples explained a very small amount of variation in the δ15N model (RG2 LMM(m) = 0.8 %), and variation in δ15N was instead explained by the combination of bird identity (Bird ID) (RLRT = 23.66, P < 0.001) and Feather ID (RLRT = 40.73, P < 0.001) in the random-effects structure of the model (RG2 LMM(c) = 87.6 %, Table 2)
Summary
Stable isotope analysis has provided the study of avian migration with vital trophic and spatial markers (Hobson 1999; Newsome et al 2007; Inger and Bearhop 2008). Combining isotopic signatures of feathers with knowledge of moult patterns has allowed the reconstruction of migration routes (Ramos et al 2009a), provided information on the possible transmission of the H5N1 strain of avian influenza (Chang et al 2008; Horacek 2011), and revealed variation in habitat preferences both within and between species during the nonbreeding period (Cherel et al 2006; Phillips et al 2009) This has enabled the migratory patterns and habitat selection of individuals during the winter to be linked to subsequent condition and breeding performance (Marra et al 1998; Furness et al 2006; Inger et al 2008) and identifies the geographical origins of pollutant burdens carried by seabirds (Leat et al 2013)
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