The babbling behavior of baby bats bears a striking likeness to babbling in human infants, a finding that researchers at the Museum für Naturkunde Berlin suggest could provide valuable new insights for biolinguistics research into the origins of human language. The team claims that their study of the greater sac-winged bat (Saccopteryx bilineata), through which they compared the bat pups’ babbling features to those that characterize babbling in human infants, represents “… the first formal analysis of bat pup babbling.”
Not only did the scientists’ analyses identify clear evidence of babbling behavior in the bats, but suggest that bat pup babbling is strikingly similar to babbling in human infants—characterized by the same eight features, including imitation of canonical syllables and rhythmicity. Suggesting that these shared components may have similar specific mechanisms in other vocal learning mammals, the team claims that the findings could pave the way to further research into the cognitive and macromolecular mechanisms and adaptive functions that underlie babbling behaviors.
“It is fascinating to see these compelling parallels between the vocal practice behavior of two vocal learning mammals,” said Mirjam Knörnschild, PhD, co-corresponding author of the team’s published paper, in 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.”
Knörnschild, together with co-corresponding and first author Ahana A. Fernandez, PhD, a former Smithsonian Tropical Research Institute (STRI) visiting scientist, and co-authors Lara S. Burchard, PhD, and Martina Nagy, PhD, described their findings in a paper titled, “Babbling in a vocal learning bat resembles human infant babbling.”
Language, perhaps more than anything else, defines human nature. Speech, the vocal output of language, requires precise control over our vocal articulators, including tongue, lips, and jaw. Every infant faces the challenge of gaining precise control over the vocal articulators to produce speech sounds. This control is gained during babbling when infants start to produce first utterances resembling speech sounds. 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 “going”), consonants (e.g., “ba” and “ga”), and rhythmicity (e.g., “da da da”) that define human language.
In fact, typical child development involves babbling irrespective of the culture and language to be learned and is thus characterized by universal features. For example, the researchers noted, “The ability to produce canonical syllables, such as “da da,” during babbling is required for successful language acquisition, and age-appropriate babbling is an indication of typical child development.”
Much of our knowledge about human language acquisition is gained through comparative research on vocal ontogenetic processes in non-human animals, especially those capable of vocal imitation, one of the key components of human language. However, babbling behavior is rare in the animal kingdom, and so far, the phenomenon has been described almost exclusively in songbirds. While research on songbirds has provided us with important insights about speech development in children, it is partly difficult to fully translate the results to humans because songbirds and humans differ anatomically—birds have a syrinx, we have a larynx—and in their brain organization.
One mammal, the greater sac-winged bat, Saccopteryx bilineata, also shows evidence of babbling, despite, at first sight, seemingly holding very little resemblance to humans. S. bilineata pups are capable of vocal imitation, and engage in a conspicuous vocal practice as they grow. This vocal practice has been described as resembling human infant babbling—and during this babbling, pups acquire territorial songs by imitating adult tutors, however, the researchers pointed out, “ … formal analyses have been lacking.”
For their reported study, the scientists studied the babbling behavior of 20 S. bilineata pups in their natural habitats in Panama and Costa Rica. To collect data, the bats were habituated to the presence of the researchers in close vicinity of their roosts, thus allowing daily acoustic recordings and accompanying video recordings from birth until weaning. “Working with wild bat pups is a unique opportunity because it allows observing and recording a complex behavior in a completely natural undisturbed setting,” explained Fernandez.
As they grow and develop, S. bilineata pups spend on average seven weeks engaging in daily babbling behavior. “Pup babbling started within the first three weeks after birth, at approximately one-third of the way through their 10-week vocal ontogeny,” the team noted. This pup babbling is characterized by different vocal sequences, which include syllable types of the adult vocal repertoire. “Pup babbling bouts consisted of undifferentiated protosyllables and adultlike syllable types,” they continued. “During babbling, pups acquire territorial songs by imitating adult tutors.” Nagy added, “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 minutes, and while babbling, pups learn the song of the adult males.”
Fernandez further commented, “While babbling, pups learn a part of the adult vocal repertoire through vocal imitation of adult tutors. 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.”
Back in the laboratory, the acoustic recordings were evaluated to analyze the characteristics of the pup vocalization. The researchers found pup babbling to be characterized by the same eight features as human infant babbling. “For example, pup babbling is characterized by reduplication of syllables, similar to the characteristic syllable repetition—“da da da”—in human infant babbling,” said Burchardt. Moreover, they found the pup babbling rhythmicity occurred in both male and female pups—which stands in strong contrast to songbirds, where only young males babble.
The authors further suggested, “Undifferentiated protosyllables may be comparable to speech precursors in human infants [i.e., sounds not commonly used in mature speech], whereas adultlike syllable types may be comparable to the canonical syllables produced by babbling human infants [i.e., acoustic structure clearly reminiscent of fully developed adult syllable types].”
The authors suggest that the similarities in babbling features between two species with common traits, including laryngeal sound production, similar brain architecture, and vocal production learning, could help scientists gain new understanding of shared cognitive skills and neuromolecular foundations. “These parallels in vocal ontogeny between two mammalian species offer future possibilities for comparison of cognitive and neuromolecular mechanisms and adaptive functions of babbling in bats and humans,” they concluded. “These parallels in vocal ontogeny between two mammalian species offer future possibilities for comparison of cognitive and neuromolecular mechanisms and adaptive functions of babbling in bats and humans.”