What bats may do better: Emission beampattern complexity

Horseshoe bats (family Rhinolophidae) and the related Old World round-leaf nosed bats (Hipposideridae) have conspicuous emission baffles (“noseleaves”) that not only have a high degree of geometric complexity but can also change their shapes under active muscular actuation during emission of the biosonar pulses. Our work has shown that these shape changes occur in tight synchrony with pulse emission and are large enough to affect the acoustic diffraction process. Furthermore, our experiments with bats positioned on an experimental platform have shown that these noseleaf motions impart dynamic signatures onto the emitted ultrasonic wave packets. We also have collected pilot data from flying bats executing natural maneuvers that indicate geometric complexity as well as time-variance in the beampatterns based on a comparison with a loudspeaker that was placed in the same position as the bat to serve as a static reference. An information-theoretic analysis has shown that this emitter dynamics results in the encoding of additional sensory information that is useful, e.g., for direction finding, but future work is needed to determine if and how these effects may fit into the animals' natural biosonar behaviors. It remains to be seen if dolphins are make use of a similar biosonar emission dynamics.