Adaptive echolocation and flight behaviors in free-flying bats, Eptesicus fuscus

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Echolocating bats emit ultrasonic sonar pulses and listen to returning echoes, which are reflected from targets or obstacles, to probe their surroundings. Their biological sonar system is well-developed and highly adaptive to the dynamic acoustic environment. Bats are also agile flyers and they can modify their flight behavior in order to capture insects efficiently. Adaptable echolocation and flight behaviors evolved in bats in response to environmental demands. This study employed changes in the external ear of bats and in the acoustic environment to examine how the big brown bat, Eptesicus fuscus, modifies its echolocation call design and flight patterns to cope with these new experimental conditions.

Study one investigated the influences of changes in sound localization cues on prey capture behavior. The tragus, which is part of the external ear, is believed to contribute to sound localization in the vertical plane. Deflecting the tragus affected prey capture performance of the bat, but it adapted to this manipulation by adjusting its flight behavior. The tragus-deflected bat tended to attack the prey item from above and show lower tangential velocity and larger bearing from the side, compared with its flight pattern in the tragus intact conditions. The bat did not change its echolocation call design in the tragus-deflected condition.

Study two paired two bats together and allowed them to perform a prey capture task in a large flight room. Echolocating bats showed two adaptive strategies in their echolocation behavior when flying with another conspecific. The bat either stopped vocalizing or increased its difference in call design from the other bat. In addition, one bat tended to follow another bat when flying together and antagonistic behavior was found in male-male and female-male pairs. The pursuit strategy the bat uses to track another bat is different from the strategy it uses to capture flying insects. 

This thesis confirms that the big brown bat's echolocation and flight behaviors are highly adaptable and describes several strategies the bat employs to cope with changes in sound localization cues and conspecific interference.