Unlike birds that learn their songs or mammals that learn how to hunt, bats are born knowing how to make sound waves above human hearing to catch their prey, according to a new study. The researchers, surprised by the results, expect this to be the case in all bats, as brain structures are similar across species.
To be able to find their prey in the dark and avoid crashing into trees, bats rely on a remarkable navigation system called echolocation. They produce sound waves above the human hearing that bounce off objects in the environment, and based on how the sound comes back to them, they can tell how near or how far they are to other objects. Their ears are fine-tuned to recognize their own calls.
Bats can estimate the position of the object based on the time that elapses between the moment the sound wave is produced and the moment it is returned to the bat. This calculation depends on the speed of sound, which can vary in different environmental conditions, such as air composition or temperature -- and bats carry out this calculation instinctively.
Since this was discovered more than 80 years ago, researchers have been trying to figure out whether bats acquire the ability to measure the speed of sound over the course of their lifetime or are born with this innate and constant sense. Now, researchers from the Tel Aviv University in Israel have the answer.
Zoom in on bats
Eran Amichai and Yossi Yove did an experiment through which they manipulated the speed of sound. They trained eight adult Kuhl’s pipistrelle bats (Pipistrellus kuhlii) to fly to a perch within a chamber, enriching the air composition with helium to increase the speed of sound. Helium is less dense than other atmospheric gases so sound travels faster through it.
The researchers raised bat pups and adult bats under these conditions and neither were able to adjust to the new speed of sound. They consistently landed in front of the target, indicating that they perceived the target as being closer, which means they didn’t adjust their behavior to the higher speed of sound.
This happened both in the adult bats that had learned to fly in normal environmental conditions and in the pups that learned to fly in an environment with a higher-than-normal speed of sound. For the researchers, it means that the rate of the speed of sound in bats is innate, instead of learning it -- they have a constant sense of it.
But that wasn’t the only conclusion of the study. The researchers found out that bats don’t actually calculate the distance to the target according to the speed of sound. As they don’t adjust the speed of sound encoded in their brains, they also don’t translate the time it takes for the sound waves to return into units of distance.
“Bats do not measure distance, but rather time, to orient themselves in space. This may sound like a semantic difference, but I think that it means that their spatial perception is fundamentally different than that of humans and other visual creatures, at least when they rely on sonar. It's fascinating to see how diverse evolution is in the brain-computing strategies it produces,” Yovel said in a statement.
It's mind-bending when you think about it, almost like a superpower. But then again, if you're a mammal that flies and navigates using sound, developing superpowers is probably what you need to survive.
The study was published in the journal PNAS.
