Natural Wonders & Evolution: crickets hear bat ultrasound (Evolution)

by David Turell @, Wednesday, July 29, 2020, 20:26 (83 days ago) @ David Turell

And hearing it they avoid being eaten by bats:

https://www.scientificamerican.com/podcast/episode/cricket-avoids-being-bat-food-by-doi...

"Echolocation is great for hunting. But Holderied says it’s also a potential weakness for bats—because in the ultrasonic world, these calls are very, very loud.

“'And once you have cracked that, once you have evolved an ear that lets you hear these calls, you can simply fly away and escape into safety....”

"Which the cricket has learned to do.

“'Basically, they have a response threshold–that’s what we call it. So they only respond to sounds that are very loud.”

"And how do they respond? Well, they simply stop flying—and plummet toward the ground.

"The sword-tailed cricket can discern bats’ echolocation signals by only responding to calls of a certain volume—at which point it plummets out of their approach.

“'A rain forest is a very noisy environment. There’s insect sounds, bird sounds; there’s leaves rustling. And all of this makes it harder for you to detect something you want to hear.”

"Holderied is particularly interested in sounds from the ultrasonic range—these are frequencies our ears can’t detect. But they come in loud and clear for a sword-tailed cricket in Panama.

"Holderied and colleagues at the Universities of Bristol and Graz in Austria, recently discovered the sword-tailed cricket has a novel survival strategy when it comes to life in their noisy environment.

“'Up there, it’s mainly other insects that produce noises that stop you from detecting what you really want to detect—and that is a predator that might attack you.”

"Every night, hundreds of species of hungry bats fly around the rain forest and use echolocation to hunt for their meals, which can include the cricket.

“So we are talking neotropical rain forests, and they teem with different bat species. And most of them, or many of them, would be after insects. So the frequencies that they use to find the insect prey are covering pretty much a full echolocation-frequency range.”

"Echolocation is great for hunting. But Holderied says it’s also a potential weakness for bats—because in the ultrasonic world, these calls are very, very loud.

“'And once you have cracked that, once you have evolved an ear that lets you hear these calls, you can simply fly away and escape into safety....”

"Which the cricket has learned to do. (my bold)

“'Basically, they have a response threshold–that’s what we call it. So they only respond to sounds that are very loud.”

"And how do they respond? Well, they simply stop flying—and plummet toward the ground.

“'Sometimes they don’t even drop all the way to the ground. So if the calls are louder, they stop flying for a longer period of time–that means a longer drop. But if they stop for just a half a second, that might not be enough time for them to hit the ground. And after this half a second, they start flying again, but they’re never actually crashing. But they drop out of the bat’s approach vector.'”

Comment: How did crickets learn to do this? See the bold. It involves lots of analytic thought summarizing the sound, noting that bats appear for meals. Analysis by cricket survivors must be achieved and passed on to all crickets. How is that done? Not language. I'll stick with implanted instinct. Just as with the bees biting rose leaves causes more immediate flowering. Bee waggling dances transmit concrete ideas of distance and direction to good flowers, nothing more. Where did that come from? Only dhw knows: they think like we do.


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