Using stable isotopes to study diet shifts under climate change in the Alpine swift

Climate change is altering insect communities worldwide, with potentially important consequences for insectivorous birds. Most research has focused on changes in prey abundance, but shifts in food quality may be equally important. In particular, changes in the relative contribution of aquatic and terrestrial insects to the diet could matter because these insect groups differ in nutritional value. In Alpine swifts monitored since 1999, nestling growth rates have increased over the past 25 years in parallel with rising summer temperatures, despite potential changes in flying insect abundance over the same period. Whether climate-driven changes in prey composition, rather than prey abundance alone, contribute to these changes in growth and their consequences for survival remains unresolved. Carbon (δ13C) and nitrogen (δ15N) isotope ratios in nestling feathers can help address this question, as δ13C reflects dependence on different primary producers and δ¹⁵N reflects trophic level, together informing on the relative contribution of aquatic and terrestrial insects to the diet.

This MSc project aims to (1) calibrate stable isotope ratios (δ13C, δ15N) in nestling feathers as indicators of diet composition, and then use these calibrated isotope ratios to (2) investigate changes in nestling diet over the past decades as well as (3) explore the importance of climate-linked diet changes in driving variation in nestling growth and survival.

You will analyse bulk stable isotopes (δ13C, δ15N) in nestling feathers and in the major groups of insects collected from food boluses. Comparing isotope values between prey and feathers will allow you to validate feather isotope ratios as indicators of nestling diet. This calibration will then be applied to isotopes in feathers archived over more than 20 years, allowing to reconstruct seasonal and annual variation in the diet. These records will then be linked to the long-term demographic database to test whether early-life diet composition correlates with variation in nestling development.

We are looking for a student interested in nutritional ecology and isotope analyses. The project is primarily office- and laboratory-based, with the opportunity to join the Alpine swift fieldwork during the breeding season. Previous experience with R for statistics and an interest for detailed laboratory work are desirable. The project would ideally start before March 2027.

This project is part of the SNSF-funded PhD project of Lara Hinninger on Linking climate change to changes in nutrition, physiology and life history in a long-lived insectivorous bird. You will jointly be supervised by Lara and Pierre Bize (Swiss Ornithological Institute/UNIL). The lab work will take place at the Swiss Ornithological Institute in Sempach and at the Eawag in Kastanienbaum, where Cornelia Twining (Eawag/ETH) will provide expertise on stable isotope analysis.