Pups of the greater sac-winged bat develop their vocal skills by babbling in a similar way to human babies — a discovery that could help researchers to explore the underlying neuroscience of how mammals learn to communicate with one another.
“Even though there are millions of years of different evolutionary pathways between bats and humans, it’s astonishing to see such a similar vocal practice behaviour leading to the same result — acquiring a large vocal repertoire,” says Ahana Fernandez, an animal behavioural ecologist at the Berlin Museum of Natural History and a co-author of the study, which was published on 19 August in Science1.
Human babies babble to practise speech sounds, which require precise motor control over their voice boxes, research suggests. Young songbirds also babble, but there are very few other recorded examples of babbling behaviour among animals — the bat research is the first to identify baby babble produced by a mammal that isn’t a primate. Like humans, bats need extraordinary control over their vocal apparatus, because they rely on their calls to navigate and find food through echolocation, and to communicate during courtship and mating, says Fernandez.
To understand how greater sac-winged bat (Saccopteryx bilineata) pups learn to communicate, Fernandez and her colleagues recorded 216 babbling bouts in 20 wild bat pups in Costa Rica and Panama. The researchers used ultrasonic sound equipment to capture the individual ‘syllables’ of the pups’ high-pitched squeals, and identified most of the 25 different syllables heard in the vocal repertoire of adult bats.
The team converted these audio snippets into images called spectrograms that show the pitch and intensity of the sound over time. This enabled them to search for eight key features that characterize babbling in human babies, including repetition of syllables and rhythm in the sounds. Their analysis found that the bats’ babble had all eight of these features.
Surprisingly, both male and female bats learnt and produced the syllables that make up the adult male territorial song. The females might use their experience in producing these sounds to help them make mating decisions later in life, the authors suggest.
“It’s interesting to see the similarities in babbling between bats and humans, given the differences between human language and how bats use their vocalizations,” says Jill Soha, an ethologist at Duke University in Durham, North Carolina, who studies vocal development in songbirds. The researchers analysed an “impressive number of syllables” without disturbing the bats, she adds.
Mirjam Knörnschild, an animal behavioural ecologist at the Berlin Museum of Natural History and a co-author of the study, accidentally discovered the bats’ babbling behaviour more than 17 years ago, when she was working on her master’s degree thesis. “You hear these bats and you immediately think of [human] babies,” she says. Although she and her colleagues reported these findings in 20062, some scientists were sceptical that the sounds represented true babbling. The new comparison of the bat pups’ vocalizations with those of human infants should put those doubts to rest, Knörnschild says.
Analysing the bat pups’ brains could help researchers to study the fundamental processes involved in vocal learning, she adds. “These bats are basically waving a red flag, telling us, ‘I am learning right now!’” Knörnschild says. “That means we can ask questions like: what’s going on in the brain while the bat is babbling? Or, what sort of environment do they need to learn better?”
Fernandez, A. A., Burchardt, L. S., Nagy, M. & Knörnschild, M. Science 373, 923–926 (2021).
Knörnschild, M., Behr, O. & von Helversen, O. Naturwissenschaften 93, 451–454 (2006).