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Bats as Fighter Pilots


Bam! Bam! That’s how fast a bat can hit two targets separated by different angles. Japanese scientists were intrigued at the accuracy of bats hunting their prey, so they decided to investigate. They found out something interesting. Bats can plan their attack trajectories to hit multiple targets in sequence with a minimum amount of energy. To do this, they have to focus their attention on multiple targets at once. And, as we all know, they do it primarily with sound, not sight.

Most hunting animals focus on the immediate object of prey. It’s quite a skill to sense multiple targets and quickly plan the best way to hit them. Good skeet shooters can do this with lots of practice, but bats come with the programming built in. Writing in the Proceedings of the National Academy of Sciences, the researchers summarize what they found:

When seeing or listening to an object, we aim our attention toward it. While capturing prey, many animal species focus their visual or acoustic attention toward the prey. However, for multiple prey items, the direction and timing of attention for effective foraging remain unknown….. Here we show that bats select rational flight paths to consecutively capture multiple prey items. Microphone-array measurements showed that bats direct their sonar attention not only to the immediate prey but also to the next prey. In addition, we found that a bat’s attention in terms of its flight also aims toward the next prey even when approaching the immediate prey. Numerical simulations revealed a possibility that bats shift their flight attention to control suitable flight paths for consecutive capture…. These findings indicate that bats gain increased benefit by distributing their attention among multiple targets and planning the future flight path based on additional information of the next prey. These experimental and mathematical studies allowed us to observe the process of decision making by bats during their natural flight dynamics. [Emphasis added.]

A human fighter pilot with this ability would be able to dart into oncoming planes and shoot them down in rapid succession, turning on a dime between hits. This is Star Wars tech. Han Solo in the Millennium Falcon could hardly do better.

A bat can capture two insects in less than a second. What’s required to achieve this level of flight performance? For one, the bat has to be able to adaptively change the characteristics of its sonar beam depending on the situation. It also has to be able to turn the beam quickly to the next insect while approaching the first. Then, it needs to design a flight path to hit them both in rapid succession by the most economical path.

Using both experimental and mathematical models, the scientists determined that bats routinely design the most “rational” flight path to successfully hit multiple targets.

Hence, wild echolocating bats plan their flight paths by distributing their attention among multiple prey items, which means that the bats do not forage in a hit-or-miss fashion but rather spatially anticipate their future targets for optimum routing.

If you’ve ever watched bats on the hunt in the evening, you know that they continue this rational flight planning continuously for hours, sometimes all night. It would be like a shooter facing a thousand skeet launched every 1-5 seconds in a 360-degree, 3D field and hitting every one for hours on end — all while avoiding other individuals that are doing the same thing in the same space. And insects, we know, don’t fly in straight lines or curves like skeet; they make sudden turns, too. Yet every night, each bat takes on this challenge as a matter of course.

In the past we have discussed optimization as an example of intelligent design science in action. One way the bat selects the optimum flight path is by getting both insects into the sonar beam.

This result demonstrates that the bats select their flight paths to effectively capture multiple prey items. Such parameter sets suggest that bats take a path in the direction of the next prey just before capturing the immediate prey, so that they can acoustically view both prey items (Fig. 1C). In other words, bats might select their flight paths to keep both prey items within their sonar beam.

The actual behavior of the bats, though, is even more complex than the scientists’ mathematical model.

On the other hand, bats in the wild varied dynamically their parameter set (flight attention) from moment to moment as they approached multiple prey items (Figs. 3F and 4A). This result implies that the bats actually use a more complex behavioral strategy that has not been assumed by the current mathematical model.

Insect hunting on the wing is hard work. Bats expend 14 times their basal metabolic rate while hunting. They can’t afford to waste energy. By rationally designing the most efficient routes, we might say they get the “most buck for the bang” — i.e., the most caloric intake for the exercise.

Computer techs might be familiar with time-sharing algorithms. When multiple processes are competing for the same CPU, the operating system gives each one a time slice. It returns to unfinished work when a given process gets its next turn. But not all processes are equal; some have higher priority. An operating system designer’s challenge is to rank the processes by priority and distribute the time slices fairly so that no process is ignored, but the higher priority processes get preference. Bats do this automatically. They have two competing processes, sonar and flight. In addition, each insect in the vicinity must get its share of attention:

For multiple targets, it is beneficial for bats in the wild to distribute their sonar attention and flight attention among multiple targets and to plan the future flight path based on the next prey for effective foraging. On the other hand, pipistrelle bats in the wild alternately and rapidly shift their sonar attention. This fact suggests that bats process echo streams from multiple targets in a time-sharing manner and then select the optimal flight path to capture and hunt a lot of airborne insects. These findings and suggestions originated from the unique capabilities of bats to fly while actively emitting sonar signals.

Does anybody know of a time-sharing central processor that was not designed by intelligent agents? Maybe that’s why the Japanese scientists never referred to evolution in their paper. The scientists selected the bats, and the bats selected their targets, but “natural selection” never got a time slice in the research.

Image: Mexican free-tailed bats, by dizfunkshinal (DSCF2177) [CC BY 2.0], via Wikimedia Commons.

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