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Dietary studies in birds of prey involve direct observation and examination of food remains at resting and nesting sites. Although these methods accurately identify diet in raptors, they are time-consuming, resource-intensive, and associated with biases from the feeding ecology of raptors like Gyps vultures. Our study set out to estimate diet composition in Gyps vultures informed by stable isotopes that provide a good representation of assimilated diet from local systems.\ud We hypothesized that differences in Gyps vulture diet composition is a function of sampling location and that these vultures move between Serengeti National Park and Selous Game Reserve to forage. We also theorized that grazing ungulates are the principal items in Gyps vulture diet.\ud Through combined linear and Bayesian modeling, diet derived from δ13C in Gyps vultures consisted of grazing herbivores across sites, with those in Serengeti National Park consuming higher proportions of grazing herbivores (>87%). δ13C differences in vulture feather subsets did not indicate shifts in vulture diet and combined with blood δ13C, vultures fed largely on grazers for ~159 days before they were sampled. Similarly, δ15N values indicated Gyps vultures fed largely on herbivores. δ34S ratios separated where vultures fed when the two sites were compared. δ34S variation in vultures across sites resulted from baseline differences in plant δ34S values, though it is not possible to match δ34S to specific locations.\ud Our findings highlight the relevance of repeated sampling that considers tissues with varying isotopic turnover and emerging Bayesian techniques for dietary studies using stable isotopes. Findings also suggested limited vulture movement between the two local systems. However, more sampling coupled with environmental data is required to fully comprehend this observation and its implications to Gyps vulture ecology and conservation.

We present the isotopic discrimination between paired skin and bone collagen from animals of known life history, providing a modern baseline for the interpretation of archaeological isotopic data. At present, the interpretation of inter-tissue variation (Δ(skin–bone)) in mummified remains is based on comparisons with other archaeological material, which have attributed divergence to their contrasting turnover rates, with rapidly remodelling skin collagen incorporating alterations in environmental, cultural and physiological conditions in the months prior to death. While plausible, the lack of baseline data from individuals with known life histories has hindered evaluation of the explanations presented. Our analysis of a range of animals raised under a variety of management practices showed a population-wide trend for skin collagen to be depleted in 13C by –0.7‰ and enriched in 15N by +1.0‰ relative to bone collagen, even in stillborn animals. These results are intriguing and difficult to explain using current knowledge; however, on the basis of the findings reported here, we caution any results which interpret simply on differing turnover rates. We hypothesize that there may be a consistent difference in the routing of dietary protein and lipids between skin and bone, with potentially on-site synthesis of non-essential amino acids using carbon and nitrogen that have been sourced via different biochemical pathways.

Rationale? \ud The study of insect migration is problematic due to the small size of insects. Stable isotope analysis can be used to elucidate movement, either by geographic assignment of location of a species, or by simply distinguishing migrant from resident populations. There are few isoscapes of any kind in the UK/Ireland available for interrogation. Thus, I have measured stable isotope ratios (of H, C, N and S) of 299 individuals of the non-migratory Brimstone moth (Opisthograptis luteolata) collected from 93 locations around the UK and Ireland by citizen scientists.\ud \ud Methods: \ud After removing lipids, stable isotope ratios were measured by continuous flow isotope ratio mass spectrometry, using either a conventional elemental analyser (C, N and S) or a high temperature, thermal conversion elemental analyser in reductive mode.\ud \ud Results: \ud Maps (isoscapes) were constructed that illustrate the stable isotope spatial distribution of this insect. These are the first isoscapes of H, C, N and S of biological samples covering both UK and Ireland.\ud \ud Conclusions: \ud The insect isoscape patterns can be explained from what we know of moth diet, climate and geology. Sulfur isotopes may be of particular use for distinguishing individuals from areas of unique geology. Isoscape patterns may (with care) predict isotope compositions of other, herbivorous, non-aquatic, chitinous taxa. Such isoscapes, when extended beyond the UK and Ireland, would provide a useful tool to elucidate insect migration.

Figure S1: a) Skin of SH12, a five-year-old Shetland Ewe who was in poor health prior to death. Note the large patch across the trunk where the wool has fallen off ante-mortem. b) Skin of SH12. Close up of the wool-less area. c) Skin of SH03, a six-month-old Shetland Ram who was in poor health prior to death. Despite this, the fleece and skin were in very good condition, comparable to those of healthy sheep. d) Skin of SH03. As with the hair-side, the flesh-side was in very good condition. e) Skin of SH13, a twenty-four day old Shetland Ram who died of unknown natural causes. Unlike SH12, this sheep had a thick fleece despite its young age. The hairless patches are the armpits and groin. f) Skin of SH28, a twenty-month old Leicester Longwool who was in good health prior to death. Here the wool has been removed post-mortem to reveal the uniform surface of the skin, typical of healthy sheep.