We humans live in such an audio bubble, with a hearing range of a mere 20 to 20,000 Hz (referred from here on as 20 kHz). Anything below this range is known as infrasound, and above that frequency ceiling is what we call ultrasound, or the wild chatter of the ultrasonic.
There are many creators of such lofty sounds — and sorry, Metropolitan Opera, but Audrey Luna’s high A (at about 1,760 Hz) falls very short of that mark. Over 1,100 of the world’s bat species use these ultrasonic frequencies via echolocation to find their tucker in the deep dark night. Most use their mouths, but around 300 or so species use their noses, and one customer, the ghost-faced bat, uses its lips to emit sounds up to an ear-stretching frequency of 160 kHz.
In direct response to the insectivorous interests of said bats, the greater wax moth, a tasty bat snack, evolved the ability to hear up to a whopping 300 kHz and has been identified as being able to communicate at similar frequencies to help them avoid Batmen and Batwomen from scoffing them so easily.
Under the seas, dolphins, porpoises and toothed whales like orcas, narwhals, and sperm whales, also employ echolocation, using their melon — an oval shaped fatty organ at the front of their heads — as a sonic lens. Many of their beautiful clicks and whistles, and their famous whale songs, are audible to us, but these marine mammals can “vocalize” right up to 175 kHz without hesitation.
A closer primate relative, the tiny Philippine tarsier, chit chats away in the tops of the trees at frequencies up to 90 kHz, keeping things legit up in his predator-free zone, while adult sloths also emit ultrasonic sounds as warning signals.
+ Read more on Flypaper: “How to Find Your Vocal Range and Write It on Your Résumé”
The lonely males of a tropical rainforest katydid species emit the highest ultrasound frequency of any insect known so far, by rubbing its wings together in a way that creates a distortion effect. When the wings spring back into shape, it converts from elastic energy to ultrasound, kicking in at 138 kHz. Ain’t what you got; it’s how you use it.
On the amphibious front, the concave-eared torrent frog, who lives in China and resides specifically in thunderously loud waterfalls, got around its acoustically challenging environment by using ultrasound to vocalize up to 128 kHz, and having recessed ears (presumably to block out their own species’ signal from the environment’s noise).
Male mice trill a very complex song ultrasonically when they’re looking for sex, but it’s actually common rats who have had the most research done on the type and function of their vocalizing frequencies. They get more ultrasonic (up to 50 kHz) when they are in positive emotional states (appetitive). In other words, through social contact and feeding behavior, they get giddily happy.
This has been well-documented by a scientist, Jaak Panksepp, who has become known more popularly as the “Rat Tickler.” Bear with me here. His early work charted seven networks of emotions across species from humans to cats to rats. He concluded that basic emotion emerges not from the part of the brain associated with complex thought in humans, but from much more ancient, primitive pathways that exist deep within the brain.
In 1999, he discovered that rats emitted a unique ultrasonic vocalization while playing or anticipating the opportunity to play with other rats. They actually emitted a chirping sound, which he and his colleagues have interpreted as “laughter,” when being tickled by people more than during any other activity. Using a transducer that researchers have used to make bat ultrasound audible to humans, Panksepp and his colleagues made recordings of rats vocalizing when being tickled, and Bob’s your uncle, there they were… laughing! Just like humans do, they make higher pitched sounds than typical speech when they’re excited.
But here’s the best part: they love being tickled so much, that if you start to tickle a rat, it will follow your hand around for more when you stop. You can see all this adorable behavior right here:
Rumor has it that the Beatles recorded an ultrasonic dog whistle for the mysterious Sgt. Pepper’s Lonely Hearts Club Band inner LP groove that follows “Day in the Life.” Maybe think about popping one of those sounds on your next album, and watch as legions of rats, bats, and dolphins come flocking to your next gig! Meanwhile, I’m going to empty our rat trap…eek!
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