Abstract
Animal migration has fascinated humans at least since Aristotle’s time, but we only started to understand itsdetails thanks to the famous “arrow storks” in the 19thcentury that returned to Europe with arrows in their bodies, providing the first clues of African wintering sites. Bird migration has received a large amount of attention since then, but knowledge about migration of other organisms, even small passerine birds, remains rudimentary (Bowlin et al. 2010).
Documenting individual migration altitudes is particularly important because of increasing densities of wind power turbines—a major cause of migrating bat mortality (Voigt et al. 2012). Suitable GPS devices for these small animals have only recently been developed, are still relatively heavy, and require relocating the logger. This necessitates additional approaches to study individual three-dimensional movement.
Development of miniaturized barometric pressure radio transmitters (Sparrow Systems, Fisher, IL, USA) encouraged us to follow the three-dimensional paths of migrating noctules (Bowlin et al. 2015).
Individual migratory flights differed, both within and among individuals. This is similar to Swainson’s thrushes, which show a large amount of variation intiming, duration, and altitude of individual tracks (Bowlin et al. 2015). This suggests that individuals make decisions to take advantage of wind, landscape, and navigational conditions or other, yet-unknown factors, to optimize their nightly flights. Our results once more confirm that the flexibility and behavioral repertoire of individuals in the wild are greater than we assume. More work is necessary to understand the threats and challenges common noctules and other migrating species encounter as they move across the landscape, particularly as over 40% of our observations were within the sweep range of most wind turbines inGermany.