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BABBLING BABY BATS

WHAT WITH COVID and all, bats have had particularly bad press of late. However, science comes to a rehabilitation of their reputation: It turns out the greater sac-winged bat, Saccopteryx bilineata, is a rare mammal sharing the human trait of babbling.

Cathleen O’Grady writes in Science, August 19, 2021, “Baby Bats Babble, Much Like Human Infants.” Here are tidbits from her article, from the technical paper it summarizes, and from my usual Internet sleuthing.

Bat Songs. O’Grady says, “Adult male sac-winged bats sing complex songs, much like songbirds, to defend their territories and attract mates. These sounds are made up of strings of 25 different distinctive ‘syllables.’ During infancy, the pups produce the syllables over and over again, seemingly practicing for the day they’ll string them together into full songs.”

According to Wikipedia, the species’ infant babbling “is the first example of mammal babbling outside of the primate family.”

The greater sac-winged bat is native to Central and northern portions of South America. The species gets its name from small pouches used by males to hold and distribute secretions attracting females and identifying harem territories. Image from Science, August 20, 2021.

Researchers Trek Through Costa Rica and Panama. Full details of the research are given in “Babbling in a Vocal Learning Bat Resembles Human Infant Babbling,” by Ahana A. Fernandez, et al, Science, August 20, 2021. She and her colleagues are associated with Berlin’s Museum of Natural History. They “investigated the undisturbed, unmanipulated babbling behavior of 20 pups from two wild populations in Costa Rica and Panama throughout the pups’ vocal ontogeny and analyzed 55,056 syllables from 216 babbling bouts.”

O’Grady observes, “Because human ears aren’t well-attuned to bat calls—and some of the frequencies are beyond our range of hearing—the researchers relied on a laptop showing visual representations of the sounds in real time. Some patterns are nice, distinct streaks—a bit like a heartbeat on a heart rate monitor, Fernandez says. Others look more like dark clouds.”

Note the range of 25-100 kHz, too highly pitched for the human ear’s range of about 20 Hz to 20 kHz. This and the following image from Fernandez et al.

O’Grady notes, “It was the first time anyone had done research like this, so all 55,000 syllables in the recordings had to be classified by hand. But now, [co-researcher] Knörnschild says, “We have this awesome database that we can use for machine learning approaches in the future.”

Sharing Human Traits of Babbling.”As in humans,” O’Grady says, “it begins early in development, and it contains a large number of repeated syllables—like a human baby saying ‘bababababa.’ ”

Both bats and humans initiate babbling with canonical utterances (human “ga,” for instance), followed by syllable reduplication (“da da”), rhythmicity (practicing cyclic use of the vocal tract), and syllable subset acquisition (universal sounds for humans or bats). 

Babbling Leads to Adult Vocalization.

Nonmandatory social content is also typical of bat and human babbling: O’Grady notes, “And unlike the ‘isolation calls’ that attract their mothers’ attention, the vocalizations didn’t seem to be a form of communication. A babbling pup is ‘a relaxed and happy pup,’ Fernandez says, ‘sitting in the day roost and just practicing and playing around.’ ”

Babbling evolves over a three-month ontogeny to maturity. Fernandez and her colleagues note, “Not a single pup acquired the entire adult repertoire of 25 syllable types at weaning age (3 months).” However, “all pups acquired the same 10 syllable types, including the syllable types belonging to the later adult territorial song.”

“Notably,” the researchers say, “both sexes acquired the syllable types constituting the adult male territorial song and produced them in the correct sequential order, even though only males sing as adults. Females’ own experience of producing song syllables might facilitate their assessment of male song, thus influencing future mating decisions.”

“Hey, cutie, how you doin’?” ds

© Dennis Simanaitis, SimanaitisSays.com, 2021  

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