Baby Bats Babble Just Like Human Infants

Bats are often portrayed in the media as spooky or threatening, associated with haunted houses and disease outbreaks. But a new study published in Science paints the flying mammals in a more adorable light. Greater sac-winged bat pups (Saccopteryx bilineata) babble just like human infants, and by studying them we can learn more about ourselves.

"We find striking parallels in the vocal practice behavior in two mammalian species that are capable of vocal imitation," study co-author Dr. Ahana Fernandez of the Museum of Natural History in Berlin tells Treehugger. "Humans and bats."

Babbling Away

The babbling stage is an important part of language acquisition in human infants. "During this time, toddlers make a range of specific sounds as they practice and imitate adult speech," the study authors explain.  

Until this study, however, there was very little evidence on whether babbling was present among other mammal species that are also vocal learners—that is, animals that can modify the sounds they make based on experience. Babbling behavior has been documented in songbirds, which are vocal learners but not mammals, as well as in pygmy marmosets, which are mammals but not vocal learners.

Babbling isn’t just another word for infant vocalization. In animals, it is different from begging behavior or isolation calls, "calls that an infant produces to solicit care," Fernandez explains. 

Isolation calls only occur in a specific context, i.e. when an animal is hungry or lost. They are also usually simple and monosyllabic. Babbling, on the other hand, can occur at any time and uses more syllables. Greater sac-winged bats, for example, "babble away in the day roost," Fernandez explains. 

This ability of the greater sac-winged bat pups was discovered by accident. Fernandez’s current supervisor and study senior author Mirjam Knörnschild had been conducting Ph.D. research on the species, but was initially focused on the songs of adult males.

"She was there during the time when the pups are born and present in the day roost, and while she was actually observing the males she ... heard ... that the pups are babbling," Fernandez said. 

Knörnschild could tell that this wasn't mere begging behavior because she could hear elements of the adult males' territorial song in the pups' vocalizations. She wanted to study this further, but was told by colleagues that the babbling behavior would be more interesting if she could first prove that the species was capable of vocal imitation. This would prove that the babbling was a learning device. 

"She actually showed that the pups learn the territorial songs, or part of the adult vocal repertoire, through vocal imitation," Fernandez says. 

Now it was time to prove that the bats were really babbling. This is was when Fernandez, who met Knörnschild a few years later once Knörnschild had established her own research group, entered the picture.

"I was introduced to the greater sac-winged bat and I had the same feeling instantly," that the bats were babbling like human infants, Fernandez says. 

To confirm this, the researchers reviewed the literature on human speech acquisition and spoke to experts in the field. Out of this, they compiled eight key features of human babbling to look for in the bats. They then observed 20 bat pups in Costa Rica and Panama over the 12-week period from birth to weaning. 

"Our findings demonstrate that babbling in bat pups is characterized by the same eight features as babbling in human infants," the study authors concluded. 

Babes and Pups 

So what exactly do the sounds of human infants and bat pups have in common? Fernandez outlines four of the "most conspicuous features."

1. Multisyllabic Babbling: Both babies and pups copy different syllables from adult speech.
2. Repeated Syllables: Both babies and bats will also repeat the same syllable multiple times, then move on to another. Think of a baby cooing, "Ba-ba-ba," then "Ga-ga-ga."
3. Rhythm: Babbling in both species is very rhythmic. This is why you can observe human babies banging on a table while they babble.
4. Early Start: Both babies and bats start babbling early in their development. For bats, it begins about two-and-a-half weeks after birth and continues until they are weaned. 

These similarities have important implications, Fernandez explains. "It’s interesting because, although phylogenetically speaking, they are so different, [bats and humans] use the same learning mechanisms to reach the same goal, to acquire a complex adult vocal repertoire."

This suggests that species that can vocally imitate and make a large range of sounds as an adult need to practice in order to develop that range. Babbling might be a necessary step in this process regardless of species. "It tells us a little bit more about our own communication system, about language," she says.

While there is limited evidence on babbling in other mammal species, Fernandez thinks porpoises and otters are likely candidates, though they are difficult to study. And the greater sac-winged bat may not be alone in this behavior.

"Considering that we have more than 1,400 bat species in the world, we will very likely find another species that is a vocal learner and also babbles," she says.

For her part, Fernandez is continuing to work with the greater sac-winged bats to determine two things—the neuromolecular foundations of their vocal learning, and how their social environment impacts their vocal learning.

Bad Press

For Fernandez, the research also has another takeaway message: Bats need better press. She noted that the animals have gotten a bad rap recently due to their potential link to the coronavirus pandemic. 

"I think bats are fascinating creatures to study social behavior and also especially vocal communication," she says.

While greater sac-winged bats are not threatened, more than 200 bat species around the world are. Fernandez suggests simple things people can do to be friends to bats.

"First of all," she advises, when you see a bat, "be happy and enjoy that the bat is visiting you in your backyard."

You can also take steps to make your yard bat-friendly by planting flowers that will attract insects, which bats can eat.