Migration is an essential process in animals’ lives, which they use to avoid adverse weather conditions and resource scarcity. Migratory animals are considered particularly vulnerable to anthropogenic changes to their environment because they require a specific temporal and spatial progression of appropriate habitats for foraging and reproduction, and a refuge from harsh environmental conditions. Anthropogenic activities that change the environment such as habitat loss, habitat fragmentation, and climate change have had a global effect on migratory species resulting in widespread population declines. Climate change is a particularly serious threat for migratory species as it can have impacts across all the habitats within which migratory animals must move. Efforts to mitigate climate change may also have adverse effects on migratory species. The trade-off between renewable energy use and wildlife conservation is not always straightforward. Changes in energy systems have the potential to alter the functioning of ecosystems and wildlife populations by affecting species' access to resources, habitat availability, and connectivity. The use of wind energy poses a particular threat for many migratory species. Studies have shown that wind energy farms pose a mortality risk to flying migratory individuals both inland and on the coast, and new concerns are being raised around offshore establishments. Conservation of migratory species in the face of such threats is of vital importance and will likely require the protection of the multiple habitats that are used during the migratory journey. However, there is often limited knowledge about the migratory pathways and stopover sites used by migratory species, posing a major challenge for effective conservation. Stable isotope analysis can be used to trace terrestrial migratory routes and identify migratory origins. The development of such techniques to determine the corridors and pathways migratory animals are using to move between habitats has assisted us in further honing conservation efforts. Stable isotope analysis allows the use of a small number of samples, which can be collected in one sampling event, to detect environmental tracers that are related to the spatial-temporal movement of animals. The application of stable isotopes in conservation biology is growing rapidly and shows great promise for the conservation of endangered species. Bats are one of the most taxonomically diverse groups of mammals, however, only a few species are known to migrate long distances. These species have evolved a combination of physiological and morphological traits to allow long-distance migration. The European Nathusius’ pipistrelle (Pipistrellus nathusii) is one of the most well-studied migratory bat species worldwide. The species is known to maintain a long-distance migration with both coastal and offshore pathways. Recent studies have shown that Nathusius’ pipistrelles have been increasing their geographical range, even reaching 60° N in latitude. Their long-distance migratory behaviour and the increase in European wind farms make them highly vulnerable to environmental changes. Considering their broad European range, high vulnerability to environmental changes, and the current need to protect migratory species, Nathusius’ pipistrelles are an interesting model species in which to apply stable isotope analysis to investigate migration patterns. In this thesis, I use stable isotope analysis to identify the northern migratory corridors of Nathusius’ pipistrelles (chapter 1) and differentiate the mortality risk posed by wind turbines on different demographic groups during migration (chapter 2). In chapter 1, I use a dual-isotope approach (δ2H and 87Sr/86Sr) to determine the origin of bats found on three islands in the north of Germany. Although δ2H analysis suggested a possible Fennoscandian origin, 87Sr/86Sr analysis refuted this possibility and proposed they would be originating in Russia and the Baltic states. In chapter 2, I use a comprehensive dataset of fur samples from carcasses collected beneath wind turbines and living individuals across Germany to assess the vulnerability of different demographic groups to wind turbine mortality. Compared to adults, juveniles were more vulnerable at low wind turbine densities; this effect was minimised at high density, with both ages equally affected. In addition, I found more females and regional migrants in both living and carcass populations. Overall, this dissertation demonstrates the importance of stable isotope analysis in wildlife research and provides a practical example of how it can help inform species conservation.
