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Sensory and cognitive ecology of species interactions in bat communities

Final Report Summary - INTERBAT (Sensory and cognitive ecology of species interactions in bat communities)

Sensory systems are at the centre of the ecological and evolutionary interactions of animals with their mates, competitors, predators and prey. The ERC-funded interBAT project investigated interspecific interactions and cognition across species boundaries and the functional role of animal sensory systems for ecological processes.

Echolocating bats and their prey are an ideal model system for this research question since their interaction depends only on acoustic information. This allows us to quantify the information generated and perceived, and to experimentally manipulate the acoustic environment.

In a series of experiments, we tested the heterospecific recognition hypothesis; i.e. asking if bats can perceive the species identity of other bat species and if they use this information for their own behavioural decision. We used loudspeaker playbacks of echolocation calls to simulate foraging bats of five different species. In two field studies and one lab experiment, we quantified the flight trajectories, foraging time and bat abundance of the trawling bat Myotis capaccinii in response to these playbacks. We found that M. capaccinii only reacted to the simulated activity of its own species and of its sister species M. daubentonii, which has a similar foraging ecology and call design. M. capaccinii did not react to calls of species which were only ecologically similar or only acoustically similar. This result supports the idea that M. capaccinii is able to perceive species identity, but only reacts to species that are very similar both in foraging ecology and acoustic call design. Further studies are needed to determine if ecological and acoustic similarity are equally important, if bats also react to species that are only ecologically similar, despite acoustical dissimilarity (and thus to clearly exclude the acoustic similarity hypothesis) and to quantify how similarity is perceived by bats.

Many bats also rely on prey-generated sounds for prey detection, localization and classification. We thus aimed to analyse the available acoustic information for detecting prey. We analysed the temporal properties of thousands of insect rustling sounds, revealing a complex picture of how prey sounds are influenced by prey taxon, prey mass and the substrate on which insect prey is walking. While amplitude and frequency information show clear correlates with prey mass and type of substrate, the temporal sound characteristics, such as roughness, rhythmicity or repetitive structure, is more variable. One parameter, the roughness which describes the temporal regularity of a sound, was strongly correlated with peak amplitude, and thus with prey mass. Since the amplitude perceived by a predator depends on the distance to prey, it is not a reliable parameter to estimate prey mass. Roughness, in contrast, is distance-independent and thus allows a predator to estimate prey mass from a distance. Redundancy in signal information makes sound signals thus robust against information loss during transmission, providing predators with information that prey inevitably emit while moving about.

In a methodological side project, we tested different labels that can be attached to scientific equipment to reduce theft and vandalism of this equipment. A friendly label that informed the public about the ongoing work in a friendly and personal voice reduced vandalism by 40-60 percent in comparison to labels in a neutral and threatening tone, respectively. We suggest that not only researchers, but also private companies, the public sector and private persons, distribute information in a detailed and friendly way to maximise impact.