Bat wing air pressures may deflect prey structures to provide echo cues for detecting prey in clutter

Abstract

Bats have remarkable echolocation capabilities to detect prey in darkness. While it is clear how bats do this for prey that is isolated, moving, or noisy, their ability to find still and quiet prey within clutter has remained a mystery. A video published by the ChiRoPing group shows the gleaning bat Micronycteris microtis capturing a still dragonfly specimen sitting on a leaf surface. While hovering over the dragonfly, the bat's wings exert air forces that cause the dragonfly wings to deflect in synchrony with the bat's wing beats. This paper illustrates that echoes from such deflecting wings vary in both amplitude and time-of-flight, producing robust echo cues that permit prey detection, even when the prey is embedded within clutter. Experiments with a dragonfly specimen mounted on a leaf driven by periodic air puffs produced wing deflections that were sensed with sonar pulses. Results demonstrate that echo variations synchronized with periodic air puffs are easily distinguishable from surrounding clutter, even when clutter produces the first echoes. These results suggest a strategy that bats can employ to detect still and silent prey embedded within cluttered environments.

Perception of silent and motionless prey on vegetation by echolocation in the gleaning batMicronycteris microtis

“…This supports the hypothesis that a terminal phase seems to be only of particular importance for tracking moving prey [50]. Just recently it has been proposed that prey perception by M. microtis could be facilitated by air turbulences produced by bat wing air forces during hovering flights through slight, induced vibrations of prey body parts [51]. Although we cannot exclude this possibility, from our results this seems unlikely, because M. microtis readily detected prey items lacking potentially vibrating body parts such as wings.…”

“…moving prey [50]. Just recently it has been proposed that prey perception by M. microtis could be facilitated by air turbulences produced by bat wing air forces during hovering flights through slight, induced vibrations of prey body parts [51].…”

Millimeter-Wave Bat for Mapping and Quantifying Micromotions in Full Field of View

“…The biosonar system of bats is exceptionally sensitive of preys with motions from large to tiny movement, allowing effectively foraging in cluttered environments. Large motions can provide cues with obvious Doppler frequency modulation; however, some species of bats (e.g., the common big-eared bat, Micronycteris microtis) have been demonstrated with outstanding capability of micromotion perception in clutter related to informative phase variations, suggesting the neural processing mechanism is just beginning to be understood [6,7,9,33].…”

Acoustic shadows help gleaning bats find prey, but may be defeated by prey acoustic camouflage on rough surfaces

“…Gleaning Myotis use short frequency-modulated (FM) broadband calls, but behavioural evidence demonstrates these bats are less efficient at this task when background ‘clutter’ obscures target echoes ( Arlettaz et al, 2001 ). Some substrate gleaners may beat their wings at potential prey to elicit movement ( Kuc and Kuc, 2012 ). True active gleaning requires the bat to distinguish a motionless target from its resting surface, which can be a highly structured background.…”