Babies learn to babble before they can talk, usually starting with the “ba-ba”, or “ga-ga”, or in the really fortunate cases – with “ma-ma”. After that, they start stringing a few random syllables together, and only after that, they actually start talking.
Songbirds exhibit the same type of behavior when they start singing, and the capacity for this sort of syllable sequencing is widely believed to be innate and to emerge full-blown — a theory that is challenged by a paper published on Nature’s website today. A study of three species, zebra finches, Bengalese finches and humans, reports that none of them has it easy – they young ones have to start stringing syllables together slowly, pair by pair.
“We discovered a previously unsuspected stage in human vocal development,” says first author Dina Lipkind, a psychologist now at Hunter College in New York.
The researchers began their study by training young zebra finches (Taeniopygia guttata) to sing a song in which three syllables represented by the letters A, B and C came in the order ABC–ABC. They then trained them to sing the same song, but in a different order – ACB-ACB. Eight out of seventeen birds managed to learn the second song, but it took them quite a while. They learned it as a series of syllable pairs, first, say, learning to go from A to C, then from C to B and finally from B to A; on average, it took them 10 days to learn the first phase, 4 days to learn the second one, and 2 for the third.
They then studied untrained Bengalese finches (Lonchura striata domestica). For instance, in this bird’s songs, some syllable pairs are reversible — sometimes syllable A comes before syllable B and vice versa. When they tracked their progress in time, they found that young birds don’t acquire the ability at the same time – that the birds acquired the two orders an average of about 18 days apart.
But the real surprise of the study was that humans follow the same pattern – when researchers analyzed databases of vocal recordings from nine infants, they found that their well-known babbling progression did not happen quickly, but rather took a period of 20-30 weeks.
“The study provides beautiful evidence of stepwise transitions in songbirds, as well as analyses that are suggestive of the same phenomenon in human infants,” says Michael Frank, a language-acquisition researcher at Stanford University in California. But he cautions that the hypothesis for babies should be tested experimentally.
Michael Goldstein, one of the world’s leading authorities in the field, questions whether the learning patterns exhibited by the finches can even be generalized across the species’ tuneful relatives.
“There’s no such thing as a generic songbird,” he says. He also points out that the study used only small sample sizes.
But still, he applauds the initiative and results of the study.
“A lot of people talk about the parallels between birds and babies,” he says, “but very few actually study them. It’s good that they’ve done this.”
Paper reference: Nature doi:10.1038/nature.2013.13090