Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Thursday, December 8, 2022

Death metal bat

My favorite wild animals are bats.

I think the flying fox -- a large diurnal species of fruit bat -- has got to be one of the coolest animals in the world.  Think about how amazing it would be, being a flying fox.  You have great big wings and can fly anywhere you want, you get to eat figs and dates all day, and you're cute as the dickens.  What could be better than that?

Fruit-eating sky puppies, is what they are.

[Image licensed under the Creative Commons Trikansh sharma, Eye contact with flying fox, CC0 1.0]

Unfortunately, bats in general have gotten a bad name, even though they're unequivocally beneficial.  (The insectivorous kinds can eat up to a thousand small flying insects -- including disease-carrying mosquitoes -- in an hour.)   The negative reputation comes from two sources: first, an association with drinking blood (only three out of the thousand species of bats do that; all three live in South America and almost never bite humans); and second, that they carry rabies (which can happen -- but so do raccoons, foxes, skunks, feral cats and dogs, and even deer).

Bats are good guys.  They're also incredibly cool.  I did a piece last year about the wild adaptations for echolocating in nocturnal bats, an ability I still find mind-boggling.  Which is why I was so psyched to run across a paper this week in PLOS-Biology about the fact that their ability to produce such an amazing array of sounds is due to the same feature death metal singers use to get their signature growl. 

In "Bats Expand Their Vocal Range By Recruiting Different Laryngeal Structures for Echolocation and Social Communication," biologists Jonas HÃ¥konsson, Cathrine Mikkelsen, Lasse Jakobsen, and Coen Elemans, of the University of Southern Denmark, write:

Echolocating bats produce very diverse vocal signals for echolocation and social communication that span an impressive frequency range of 1 to 120 kHz or 7 octaves.  This tremendous vocal range is unparalleled in mammalian sound production and thought to be produced by specialized laryngeal vocal membranes on top of vocal folds.  However, their function in vocal production remains untested. By filming vocal membranes in excised bat larynges (Myotis daubentonii) in vitro with ultra-high-speed video (up to 250,000 fps) and using deep learning networks to extract their motion, we provide the first direct observations that vocal membranes exhibit flow-induced self-sustained vibrations to produce 10 to 95 kHz echolocation and social communication calls in bats.  The vocal membranes achieve the highest fundamental frequencies (fo’s) of any mammal, but their vocal range is with 3 to 4 octaves comparable to most mammals.  We evaluate the currently outstanding hypotheses for vocal membrane function and propose that most laryngeal adaptations in echolocating bats result from selection for producing high-frequency, rapid echolocation calls to catch fast-moving prey.  Furthermore, we show that bats extend their lower vocal range by recruiting their ventricular folds—as in death metal growls—that vibrate at distinctly lower frequencies of 1 to 5 kHz for producing agonistic social calls.  The different selection pressures for echolocation and social communication facilitated the evolution of separate laryngeal structures that together vastly expanded the vocal range in bats.

NPR did a story on the research, and followed it up by talking to some death metal singers, all of whom were pretty fascinated to find out bats can do it, too.  "In a [masochistic] sort of way ... I think that when I can feel that my vocal cords are getting kind of shredded or beat up, that it sounds better," said Chase Mason, lead singer of the band Gatecreeper.  "You know, like, if there's a little taste of blood in the back of my throat, I think that I'm doing a good job...  A lot of people will compare you to sounding like a bear or something like that, like an animal growling or roaring even... I think it's cool.  It's very dark and gothic.  The imagery of a bat is always associated with the darker sort of things, like vampires and stuff.  So it definitely makes sense."

I'm still more favoring the Sky Puppy model of bats, but hey, I'm not arguing with a guy who can make noises like Chase Mason can.

In any case, add one more thing to the "cool" column for bats, which was pretty lengthy already.  It's incredible that however much we learn about nature, there are always ways it'll come back and surprise you.  That's why if you have a curious side, learn some science -- you'll never be short of new things to wonder at.


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