Auditory scene analysis in echolocating bats

• Main Author: Stidsholt, Laura
• Format: Book
• Language: English
• Published: Århus Universitet 2020
• Subjects: Auditory scene analysis; AUDITORY STREAM SEGREGATION; biosonar; echograms; echoic scenes; Echolocation; sensory volumes; Nyctalus noctula
• Online Access: https://pure.au.dk/portal/en/publications/8529070b-e288-4fa6-8352-698e89cc7576

The objective of this thesis has been to uncover how hunting bats actively control their vocalisations to receive returning echoes suited for auditory processing to guide their motor patterns for navigation and target interception. Specifically, I have used a microphone array to record the echolocation calls of bats approaching prey or targets in laboratory settings, and a novel, miniature sound and movement tag that records echo information from the perspective of hunting bats while they engage in natural behaviours in the wild. Chapter I reviews my findings in a selected broader context of echolocation in hunting bats and presents preliminary data from recent tagging studies of the greater mouse-eared bat (Myotis myotis) and the common noctule bat (Nyctalus noctula). Chapter II outlines the performance of the on-board tags based on laboratory recordings from the common noctule bat and big brown bats (Eptesicus fuscus). I show that the tag can be used to synchronously record the movement of the bats in three-dimensions, the echolocation calls and the returning echoes from their environments and most importantly their prey allowing for detailed studies of sensorimotor responses of freely behaving and hunting animals. In Chapter III, I demonstrate how two species of hipposiderid bats (Hipposideros armiger and H. pratti) change their vocalisations to receive surprisingly low echoes from different sizes of targets leading to the proposal that bats use a dynamic compression model to receive echoes in an optimal dynamic range for their hearing system. In Chapter IV, I take a seat on the back of the greater mouse-eared bats and quantify their echoic world in the wild through the sensory information they receive from their surroundings. I show how the bats adjust their flight paths, sensory volumes and update rates to reduce strong, masking echoes from background structures when capturing insects on the wing. By quantifying the actual returning echoes from those background structures and from the flying insects, I ...