Deep in the jungles of Costa Rica and Panama, Ahana Aurora Fernandez eavesdrops on bat conversations from dawn until dusk.
Armed with a microphone and sound recorder, Dr Fernandez is capturing the squeaky sounds of baby bats learning how to talk.
• Babbling is an essential phase of speech and language development in human infants
• Bats in Central and South America also learn how to “talk” through babbling
• These bat babbles follow a similar pattern to human babbling, offering clues about the evolutionary origins of language
And it turns out these bat babbles have remarkably similar patterns to human baby talk, according to a study published today in Science.
Like babies and toddlers, bat pups learn how to “talk” by copying adult sounds and repeating them to a regular beat.
While bats and humans appear totally different on the surface, Dr Fernandez said the findings could offer clues about how human speech and language evolved.
“It’s striking that two mammalian species with different evolutionary histories have the same vocal practice behaviour that leads to the same end product: to learn the adult vocal repertoire. That’s amazing,” said Dr Fernandez, one of the study’s co-authors at the Natural History Museum in Berlin.
From babbling to grown-up chatter
While it can be enough to drive some parents crazy, babbling allows babies and toddlers to begin mastering speech by learning how to control their tongue, lips and jaw to form their first words.
They start making this chatter at around four months old, starting with making sounds that imitate vowels, like “coo” and “ga”.
At around six months, babies begin slipping consonants into their babbling, blurting out sounds like “ba” and “da” in repeated sequences that have a regular beat, such as “da-da-da”.
Every “coo”, “ba” and “da-da-da” brings infants one step closer to stringing full sentences together, Dr Fernandez said.
“Without vocal imitation, we wouldn’t be able to speak or learn a language.”
But humans aren’t the only animals to babble their way to mature conversation.
Songbirds, such as zebra finches, also learn how to sing by babbling and copying the songs of adult birds.
But it’s tricky to use babbling birds as models for exploring the development of human language because their anatomy is vastly different to ours.
The greater sac-winged bat (Saccopteryx bilineata), a species found in the rainforests of Central and South America.
“These bats are very special because they really learn a part of the adult vocal repertoire from scratch through imitating their adult tutors,” Dr Fernandez said.
Capturing bat baby talk
What Dr Fernandez and her team wanted to know was whether the babbling produced by bat pups followed a similar pattern to human baby talk.
To find out, the researchers spent three months recording the babbling behaviour of 20 bat pups from eight wild colonies across Costa Rica and Panama.
They also ploughed through the literature to compile a list of human babbling features to see whether the bats’ babbles followed a similar pattern.
The team analysed over 55,000 syllables from 216 babbling bouts produced by the bat pups.
While syllables in human infant babbling consist of consonant sounds that transition into vowel-like sounds (“ba” and “ga”), bat syllables are defined as tones surrounded by silence.
The bat pups proved to be a chatty bunch from a young age, babbling away in the trees from just three weeks’ old.
By the time they were 10 weeks’ old, the pups were spending nearly half of their waking hours giving their vocal skills a workout, with a single babbling session lasting for up to 43 minutes.
Much like human babies learning how to combine vowels and consonants, the bat pups’ babbling consisted of a mash-up of syllables their parents use.
“The pups produced syllables from the adult territorial song, followed by syllables from the adult courtship song,” Dr Fernandez said.
“They completely mix them up.”
While the pups were from different colonies and locations, they all picked up the same syllables, just as humans produce similar babbling sounds regardless of the culture they are growing up in.
And just like a human baby saying “da-da-da”, the bat pups spent most of their babbling time repeating the same syllables to a clockwork-like beat.
Dr Fernandez suspects the bat pups babble repeatedly to get their communication skills up to speed and learn how to use their vocal apparatus properly.
But it’s not all hard work.
“While you’re babbling, you’re happy,” Dr Fernandez said.
“It’s not only practising and learning, but also having fun and just babbling away. It’s a comfort behaviour.”
Do Australia’s bat babies babble?
Nicola Hanrahan, an ecologist at Charles Darwin University who has studied social communication in bats, welcomed the study and said it would be interesting to explore babbling behaviour in other bat species.
“The behaviour demonstrated by greater sac-winged bats is unlikely to be restricted to this species, with a number of bat species already shown to use vocal learning,” said Dr Hanrahan, who was not involved in the study.
And while few studies have explored social communication in Australian bats, some of our native species would be good candidates for exploring babbling and vocal learning, Dr Hanrahan said.
For instance, the ghost bat (Macroderma gigas) is a very talkative species that uses its complex vocal repertoire to communicate during foraging and roosting.
“Studies into the social communication of Australian bats are few, although increasing,” Dr Hanrahan said.
“We have yet to delve into investigating the presence of vocal learning or babbling.”
The next step for Dr Fernandez and her team is to explore what is happening in the bats’ brains while they are learning how to talk.
“What is really exciting about bat pup babbling is that it shows you when learning is taking place,” Dr Fernandez said.
“Seeing what is happening in the mammalian brain during vocal learning could also tell us something about what is happening in our brain when we are vocally learning.”
abc.net.au, 20 August 2021