Abstract
Identifying migratory corridors of animals is essential for their effective protection, yet the exact location of such corridors is often unknown, particularly for elusive animals such as bats. While migrating along the German coastline, Nathusius' pipistrelles (Pipistrellus nathusii) are regularly killed at wind turbines. Therefore, we explored the paths taken on their annual journey. We used isotope ratio mass spectrometry to measure stable hydrogen and strontium isotope ratios in fur keratin of 59 Nathusius' pipistrelles captured on three offshore islands. Samples were pre-treated before analysis to report exclusively stable isotope ratios of non-exchangeable hydrogen. We generated maps to predict summer origins of bats using isoscape models. Bats were classified as long-distance migrants, mostly originating from Eastern Europe. Hydrogen analysis suggested for some bats a possible Fennoscandian origin, yet additional information from strontium analysis excluded this possibility. Instead, our data suggest that most Nathusius' pipistrelles migrating along the German coastline were of continental European summer origin, but also highlight the possibility that Nathusius' pipistrelles of Baltorussian origin may travel offshore from Fennoscandia to Germany. Our findings demonstrate the benefit of using complementary isotopic tracers for analysing the migratory pathways of bats and also potentially other terrestrial vertebrate species. Furthermore, data from our study suggest an offset of fur strontium isotope ratios in relation to local bedrock.
Highlights
Migratory behaviour is observed in a range of vertebrate taxa, including ungulates, birds, cetaceans, sea turtles and bats.[8]. Considering their small size, bats are outstanding among terrestrial mammals in their ability to cover long distances when migrating.[9,10]
Our understanding of where bats migrate remains largely speculative. This lack of knowledge has emerged as a major conservation problem since thousands of migratory bats are killed by wind turbines,[6,17,18] which are increasingly erected along coastal habitats, both onshore and offshore.[13]
Anthropogenic changes to the environment threaten many of these animals during their seasonal journeys
Summary
In the era of the Anthropocene, human-induced changes to the environment, such as land use and global climate changes, threaten a number of species, leading to a worldwide biodiversity crisis.[1,2,3] Migratory species are vulnerable to anthropogenic changes because they depend on intact breeding and wintering locations, and on a sequence of suitable and intact habitats along their migratory routes.[2,4,5] conservation efforts need to be established beyond political borders to protect suitable corridors and habitats for these highly mobile species.[6,7]. Migratory behaviour is observed in a range of vertebrate taxa, including ungulates, birds, cetaceans, sea turtles and bats.[8] Considering their small size, bats are outstanding among terrestrial mammals in their ability to cover long distances when migrating.[9,10] Yet, efficient conservation measures for the protection of migratory bats are impaired by the lack of information on migratory corridors and stopover sites.[11] Currently, it is widely assumed that coastal habitats and river valleys represent suitable pathways for migratory bats in Europe.[8,12,13,14,15] In addition, peninsulas have been identified as suitable stopover sites.[16] Other than that, our understanding of where bats migrate remains largely speculative. Nathusius' pipistrelles observed at the western capturing sites could originate from Baltorussian populations but make use of the Fennoscandian route to reach Germany via Denmark
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