Feather‐based measures of stable isotopes and corticosterone reveal a relationship between trophic position and physiology in a pelagic seabird over a 153‐year period

Abstract

Diet during the non‐breeding period influences condition and subsequent reproduction. Physiological mechanisms underlying such carry‐over effects are poorly understood but could be clarified by studying physiological responses to variation in diet during non‐breeding. The hormone corticosterone provides a functional link between diet and survival and reproduction, but methodological limitations have prevented previous studies from testing the hypothesis that, on an individual level, avian corticosterone levels during the non‐breeding period reflect broader patterns in feeding ecology during that time. Using museum specimens (1859–2002) and live birds (2012), we found that corticosterone from feathers (CORTf) is negatively related to trophic position (TP) inferred from feather stable‐nitrogen isotope values (δ15N) in Leach's Storm‐petrels Oceanodroma leucorhoa. CORTf was not related to stable‐carbon isotope values (δ13C). We detected no temporal trends in CORTf or δ15N, and neither was related to a large‐scale index of winter climate, suggesting a general ecological phenomenon rather than a reflection of historical environmental changes. However, we detected a temporal trend in feather δ13C, and δ13C was related to δ15N. Our findings suggest a physiological benefit of feeding at higher TPs, either through increased nutritional value or reduced foraging costs associated with higher TP prey, and future research should aim to distinguish between these two explanations. Nevertheless, ours is the first evidence of a correlation between individual endocrine levels and foraging ecology, and demonstrates non‐lethal variation in a physiological mediator in turn related to variation in resource use.

Museum specimens of terrestrial vertebrates are sensitive indicators of environmental change in the Anthropocene

“…R. Soc. B 374: 20170387 [93], mammals [94][95][96] and birds [89,[97][98][99], with ratios of isotopic nitrogen and carbon, in particular, providing insight into shifts in dietary regime over the past several decades. Isotopes can also be used to create 'isoscapes', maps of isotope isoclines across the landscape, allowing researchers to connect breeding and wintering ranges of migratory species [100], among other inferences such as elevational migration [101].…”

Matching geographical assignment by stable isotopes with African non-breeding sites of barn swallows Hirundo rustica tracked by geolocation

“…Herein, the tissue’s isotopic composition mirrors the source composition of the diet in a predictable manner [6]. Moreover, various tissues in a broader sense differentially archive this information on temporal scales from hours, like the composition of breath and blood plasma [7], to very long times in metabolically inert tissues like teeth [8], keratin in claws and feathers [9,10] or in hair of ancient mummies [11]. …”

Contrasting migratory responses of two closely related seabirds to long-term climate change

“…C values for changes in ocean [CO 2 ] aq due to anthropogenic carbon emissions, as the magnitude of this effect is small relative to the analytical error of our measurements (Hilton et al 2006, Quillfeldt et al 2010, Fairhurst et al 2015 …”