Babbling in human children is key to developing the careful control over the vocal apparatus necessary for speech. The study published in the journal “Science” indicates the same is true for the greater sac-winged bat, or “Saccopteryx bilineata”, native to Central America.
“Human infants seem to babble on the one hand to interact with their caregivers, but they also do that when they’re completely alone, seemingly happily just exploring their voice.
“That’s the same with what our bats are doing,” said study co-author Mirjam Knornschild, behavioural ecologist at the Museum of Natural History in Berlin.
Bats communicate by ultrasound – sound waves at frequencies above human hearing – but they can also make sounds audible to people.
“It sounds like a high-pitched twittering to our ears. It’s melodic,” said Knornschild, who has worked with bats since 2003.
Saccopteryx bilineata don’t hide away in gloomy caves but prefer to live in trees, making them easier to observe.
The babbling of 20 baby bats was recorded in Costa Rica and Panama between 2015 and 2016 by researcher Ahana Fernandez, also affiliated with the Museum of Natural History in Berlin, who spent hours with the bats in the forest.
43 minutes
The mammals, like humans, have a larynx, and start babbling about three weeks after birth, for about seven to 10 weeks until they are weaned.
During this period, the bats spend around 30% of their days babbling, with sessions lasting on average about seven minutes, the researchers calculated.
But one bat babbled for a full 43 minutes, a long stretch considering adult communication generally lasts just a few seconds.
“It’s something really, really peculiar that the other bat species which have been studied to date simply don’t do,” said Knornschild. “They’re very chatty.”
Syllables and song
Using spectrograms, the researchers analyzed more than 55,000 syllables produced by the bats, finding universal characteristics of babbling in human infants such as repetition and lack of meaning. They also found that the sounds followed a certain rhythm.
As with humans, the learning curve is not linear. Out of 25 syllables in the adult repertoire, young bats do not master all of them by the time they are weaned, suggesting they continue to learn.
The researchers were able to show that early on, the young bats learnt a six-syllable song used by males to mark their territory and attract females.
“The pups listen to adult males singing and then imitate that song,” Knornschild said.
Baby females also learn the song, even though they don’t reproduce it as adults. But the study suggests learning it may help them judge the performance of their potential future partners.