In the arms race between prey and predators, diverse anti-predator defence mechanisms evolved. To avoid predation, many insects developed camouflage (crypsis) or chemicals that render them distasteful or toxic. To warn potential predators of their unsavoury nature, many insects evolved striking warning colours or patterns (aposematism). Insects comprise most of the diet of bats. Some of these nocturnal predators glean resting, silent, motionless diurnal insects from the vegetation. Instead of using vision during foraging, they produce ultrasonic calls and detect their prey through echolocation. In my project I wanted to investigate whether insects that make use of visual camouflage or visual warning signals also have acoustic reflection properties that allow them to hide from or signal their unpalatability to echolocating bats.
In EchoBug I studied fundamental, sensory ecological and behavioural questions about insect signalling mechanisms in different sensory modalities and the differentiation of these by echolocating bats. This project aimed to understand underlying acoustic mechanisms of predator-prey interactions and inform and inspire biomimetic methods and applications for object detection and identification. The study of echolocation is of particular interest as it forces us humans that have vision as our primary sensory modality to think about how other agents/organisms that rely upon different sensory modalities can interact intelligently with their environment. Specifically, an improved understanding of how bats use echolocation and sound in general to create a rich world model supporting a broad range of intelligent behaviours provides essential guidance for the inclusion of spatial sound cues in mobility training programs for the visually impaired.
To investigate the acoustic reflections of different signalling butterflies and moths, I used the most sophisticated bio-inspired sensor system currently available to acquire echo-acoustic sonar recordings, so called echo-fingerprints, of various species. For further comparisons state-of-the-art machine learning and signal processing techniques were applied to this extensive echo-fingerprint data set. In addition, different behavioural prey-detection and -capture experiments using live bats of the species Micronycteris microtis were conducted to explore the prevailing acoustic predator-prey interactions.
The EchoBug project successfully developed a recording system that includes two high-speed cameras synchronized with a newly designed ultrasonic multi-microphone array (NI-MUMM Array. Further it created extensive data sets of lepidopteran echo-fingerprints as well as of various bat behaviours, which are currently analysed and prepared for publication. Overall, the unique combination of lab-based measurements with behavioural test allows an in-depth investigation of the underlying acoustic mechanisms of the interaction between prey and predators.
