Songbird parents change the way they vocalize when singing to juveniles, similar to how human moms and dads use "baby talk" when babbling to their infants. The findings, published in Proceedings of the National Academy of Sciences, suggest that similar mechanisms may explain how social interactions help promote vocal learning across humans and songbirds over evolutionary time.
Birds learn songs during development the same way humans learn speech. "Songbirds first listen to and memorize the sound of adult songs and then undergo a period of vocal practice – in essence, babbling – to master the production of song," McGill University’s Jon Sakata explained in a statement. Juvenile zebra finches, for example, learn by interacting with and listening to adults, especially their fathers. These birds stay with their parents until they’re about 50 to 60 days old, giving them lots of opportunities to interact with their tutors. Social interactions are critical for the acquisition of speech, but exactly how social processes support vocal learning is still a bit of a mystery.
To investigate, Sakata’s team tutored 40-day-old juvenile zebra finches using either an adult bird or via speakers. After a short period of tutoring, the birds were housed individually and left to develop their songs until they reached sexual maturity at about 120 days of age.
Socially tutored juveniles – those who got to interact with an adult – showed a significant amount of song learning compared to untutored or passively tutored birds. And that’s because adult zebra finches altered their vocalizations when singing to juveniles: Pupils paid more attention to tutors when the song had more repetition and longer pauses.
Just as human adults speak slowly and repeat themselves when talking to infants, "adult zebra finches similarly slow down their song by increasing the interval between song phrases and repeat individual song elements more often when singing to juveniles," Sakata said.
After examining the activity of neurons in a part of the brain that’s linked to attention, the team found that the neurons that produce the chemicals dopamine and norepinephrine were activated after social interactions more than after simply hearing songs through a speaker. Because of the similarities between human speech acquisition and finch song learning, the team thinks dysfunctions in these neurons in people may contribute to social and communicative disorders, like autism.
Image in the text: A juvenile zebra finch learns from an adult tutor. Jon Sakata/McGill University