NIBB and Doshisha University clarify ultrasound emission in bats — Use of multiple tactics to track prey

Researcher Nozomi Nishiumi of the Division of Behavioral Neurobiology at the National Institute for Basic Biology (NIBB), and Associate Professor Emyo Fujioka and Professor Shizuko Hiryu of Doshisha University, revealed that bats harmonize four tactics, namely target direction prediction, scan rate elevation, scan range widening, and relative motion stabilization, to greatly improve targeting accuracy in the echolocation of fleeing prey. They also proposed an integrated control framework to deploy multiple tactics. The results were published in Current Biology.

The ability to track targets to keep an object in sight is crucial for the survival of animals, but how do animals achieve accurate tracking when there is a time lag between cognition and action? The research group reanalyzed the behaviors of Japanese greater horseshoe bats (Rhinolophus nippon) recorded while they attacked moths in 2010-2011. In this experiment, the flight paths of bats were measured by high-speed cameras in a chamber, and echolocation pulses emitted by the bats were simultaneously measured by multiple microphones.

Fujioka, who conducted the experiment, said, "Since the experiment requires to pit a bat against a moth, the bat must first recognize the moth and then capture it. The experiment didn't quite work out initially as we had hoped but did finally after we tethered the moth using a string to the ceiling to force it to fly in a semicircular fashion."

They requantified all experimental data with high precision from the video analysis stage and used 3D motion analysis and computer simulation. Through this it was demonstrated that bats simultaneously deployed the four tactics of target direction prediction, scan rate elevation, scan range widening, and target direction stabilization to compensate for sensing delay and greatly improve tracking accuracy.

Nishiumi said, "The most difficult part of the analysis was setting up the effective simulation. It was quite difficult to build on the computer what the reasonable process would have been if the tactics had not been applied and what the outcome would have been under such conditions. Thus, it took several years to create the analysis system."

In addition, the simultaneous deployment of multiple tactics is difficult in practice because it requires multitasking. The research group analyzed how bats overcome these difficulties and found that all the tactics can be described as responses to a single kinematic parameter, i.e., "line of sight angular velocity." This parameter indicates temporal variations in the target direction from the bat's viewpoint. It is a measure of tracking difficulty and can also be used to predict the current target direction. This single parameter is theoretically sufficient to control all tactics by estimating the importance of tracking adjustment and predicting the target direction. In bats, the degrees of regulation of all tactics were found to correlate with this parameter. In other words, the results indicate that bats are seemingly burdened with multiple tasks, but they handle the tasks well to reduce the burden.

Previous studies have focused on individual tactical elements of animal target-tracking ability and have not addressed the strategic structure that governs different tactics. This study analyzing the strategic structure of target tracking from a broader viewpoint is expected to be followed by comprehensive studies on animals' tracking ability. The tracking mechanism reported in this study has engineering implications for sensing devices.

Journal Information
Publication: Current Biology
Title: Bats integrate multiple echolocation and flight tactics to track prey
DOI: 10.1016/j.cub.2024.05.062