Stable hydrogen isotope variability within and among plumage tracts (δ2HF) of a migratory wood warbler

Abstract

Hydrogen isotope analysis of feather keratin (δ2HF) has become an essential tool for tracking movements between breeding and wintering populations of migratory birds. In particular, δ2HF has been used to create δ2HF isoscapes that can be used to assign the geographic origins of molt. The majority of past studies have sampled a portion of a single feather as an isotopic proxy for the entire plumage although surprisingly little is known about variation of stable isotopes within and between feather tracts of individuals in local populations. Here we examine δ2HF variation in 24 pterylographic variables (9 primaries, 6 secondaries, 6 rectrices, and 3 patches of ventral contour feathers) in individual specimens of black-throated blue warbler (Setophaga caerulescens) breeding in the Big Santeetlah Creek watershed (5350 ha), southern Appalachian Mountains. By restricting our study to territorial ASY males (after second year) inhabiting a small watershed, we could focus on δ2HF variation generated during the complete prebasic annual molt in a circumscribed population while factoring out age and sexual differences in foraging behavior, isotopic incorporation, and post-breeding dispersal. Summed within-individual variation (δ2HF) across 24 pterylographic variables ranged from 12 to 60‰ (= 21.8 ± 9.4‰), with 81% of the individuals exhibiting variation ≥ 16‰ (reproducibility of analyses was ≤ 4 ‰). Adjacent feathers in feather tracts tend to have more similar δ2HF values than feathers grown weeks apart, consistent with the stepwise replacement of flight feathers. The pooled population sample exhibited significant δ2HF variation in primaries (-78 to -21‰), secondaries (-80 to -17‰), rectrices (-78 to -23‰), and ventral contour feathers (-92 to -32‰). Strong year effects in δ2HF variation were observed in each of the 24 pterylographic variables. Altitudinal effects were observed only in ventral contour feathers. The current findings demonstrate that within-individual variation (δ2HF) may be much greater than previously thought in migratory species that molt on or near breeding territories. Our study also highlights the need for greater pterylographic precision in research design of isotope-based studies of avian movement. Within-individual and within-population δ2HF variation should be incorporated in geographic assignment models. In a broader context, the staggered Staffelmauser pattern of molt in wood warblers provides an exceptional view of the seasonal variation of hydrogen isotopes circulating in blood plasma during the six-week period of annual molt.

Stable isotope (C, N, O, and H) study of a comprehensive set of feathers from two Setophaga citrina

“…While the range of δD values for the full feather set showed some variability, excluding the body feathers shows relative homogeneity for the flight feathers. This contrasts with the findings of Graves et al (2018) [ 15 ], which found δD variation within flight feathers for S . caerulescens .…”

“…There are a few possible explanations for this discrepancy. One explanation could be methodology: Graves et al (2018) [ 15 ] analyzed only the vane of the feathers, whereas both the vane and rachis were analyzed in this study. In addition, differences in the habitats, diets, and/or isotopic fractionation between the two species could also lead to detectable differences in isotopic trends.…”

“…Graves et al (2018) [ 15 ] conducted an analysis of D/H ratios for 24-feather sets (9 primaries, 6 secondaries, 6 rectrices, and 3 patches of ventral contour feathers) from specimens of the black-throated blue warbler ( Setophaga caerulescens ). That study focused on the deuterium isotope composition in territorial male specimens to analyze variability generated during the complete annual prebasic molt.…”

“…Motivated in part by the Graves et al (2018) [ 15 ] study, we use the stable isotope approach to reconstruct molt strategies and timing in two AHY (after hatch year) male Hooded Warblers ( Setophaga citrina ). In particular, we examined the isotopic variability between feathers to assess the robustness of analyzing individual feathers to infer a specimen’s ecological history.…”

Spatial and temporal diet variability of Adélie (Pygoscelis adeliae) and Emperor (Aptenodytes forsteri) Penguin: a multi tissue stable isotope analysis

“…Guano samples were cleaned, the residues of uric acid rich in inorganic nitrogen were removed with a scalpel in order to reduce any alteration during the nitrogen isotope analysis (Bird et al 2008). In order to remove surface oils and impurities, feathers were washed with a sonic bath in a 2:1 chloroform-methanol, rinsed with distilled water, dried at 60 °C in oven for at least 24 h and then cut into small fragments (Graves et al 2018).…”