Babbling is a production milestone in infant speech development. Evidence for babbling in non-human mammals is scarce. In a new study, researchers from the Museum für Naturkunde at the Leibniz Institute for Evolution and Biodiversity Science, the Freie Universität Berlin and the Smithsonian Tropical Research Institute have recorded the vocalizations of greater sac-winged bat (Saccopteryx bilineata) pups in the wild and found clear evidence of babbling that was consistent with that seen in humans.
Fernandez et al. investigated the conspicuous babbling behavior of the greater sac-winged bat (Saccopteryx bilineata), a species of bat capable of vocal production learning. Image credit: Michael Stifter.
In humans, speech requires precise control over the vocal apparatus, which enables us to make all the sounds necessary for communication.
Babbling enables infants and toddlers to practice speech sounds by gaining motor control over the vocal apparatus and making sounds that imitate the vowels (e.g., ‘cooing’ and ‘gooing’), consonants (e.g., ‘ba’ and ‘ga’), and rhythmicity (e.g., ‘da’da’da) that define human language.
However, humans are not the only vocal learners. Evidence for babbling in nonhuman mammals exists in very few species, one of which is the greater sac-winged bat.
While the babbling behavior of these bats has been likened to human infant babbling, babbling behavior in bats lacks formal evaluation.
“While babbling, pups learn a part of the adult vocal repertoire through vocal imitation of adult tutors,” said co-lead author Dr. Ahana Fernandez, a researcher at the Smithsonian Tropical Research Institute.
“This makes pup babbling a very interesting behavior because it tells us when learning is taking place and offers great opportunities to study if and how different factors, for example the social environment, influence learning success.”
Dr. Fernandez and colleagues investigated the babbling behavior of baby bats by recording the vocalization of 20 bat pups in the wild.
They compared these pups’ babbling features to those that characterize babbling in human infants.
Not only did they find clear evidence of babbling behavior, according to their findings, bat pup babbling is strikingly similar to babbling in human infants — characterized by the same eight features, including imitation of canonical syllables and rhythmicity.
“Pup babbling is a very conspicuous vocal behavior, it is audible at a considerable distance from the roost and babbling bouts have a duration of up to 43 min, and while babbling, pups learn the song of the adult males,” said co-author Dr. Martina Nagy, a researcher in the Museum für Naturkunde at the Leibniz Institute for Evolution and Biodiversity Science.
“Pup babbling is characterized by reduplication of syllables, similar to the characteristic syllable repetition in human infant babbling,” said co-author Dr. Lara Burchardt, a researcher in the Museum für Naturkunde at the Leibniz Institute for Evolution and Biodiversity Science and the Freie Universität Berlin.
“Moreover, pup babbling is rhythmic and occurs in both male and female pups — which stands in strong contrast to songbirds where only young males babble.”
“It is fascinating to see these compelling parallels between the vocal practice behavior of two vocal learning mammals,” said co-lead author Dr. Mirjam Knörnschild, a postdoctoral researcher in the Museum für Naturkunde at the Leibniz Institute for Evolution and Biodiversity Science.
“Our study is contributing to the interdisciplinary field of biolinguistics, which focuses on the biological foundations of human language to study its evolution.”
“Work on a vocal learning, babbling bat species may ultimately give us another piece of the puzzle to better understand the evolutionary origin of human language.”
“The findings would not have been possible without a deep understanding of our bats’ natural and social history for which long-term data is essential.”
The study was published in the journal Science.
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Ahana A. Fernandez et al. 2021. Babbling in a vocal learning bat resembles human infant babbling. Science 373 (6557): 923-926; doi: 10.1126/science.abf9279
