NEURONS IN ZEBRA finch brains operate as a “barcode reader” to identify songs of the same species during learning, a new study has found.
It is well documented that juvenile birds learn to sing by mimicking vocalisations of adults of the same species during development, and that juveniles “favourably learn” their own species’ song, even in noisy environments with a variety of different birdsongs. But just how juvenile birds recognise their species’ song has remained a mystery.
Now, researchers at the Okinawa Institute of Science and Technology Graduate University (OIST) in Japan have discovered a characteristic mechanism for species identification based on the silent gaps between birdsong syllables.
“We co-designed an experiment that works within the constraints of neuroscience while satisfying the requirements of physics,” explained Professor Mahesh Bandi from the OIST.
In the experiment juvenile zebra finches were raised by Bengalese finch foster parents. This was to examine how their song developed under the tutoring of a different species.
According to researchers, birdsong is comprised of stereotypical repeats of certain syllables, called “song motifs”, with syllables separated by silent gaps. The fostered zebra finches learned morphology (particular structures and patterns) of Bengalese finch syllables, including syllable duration, but transposed onto them zebra finch silent gap patterns.
Professor Yoko Yazaki-Sugiyama said this suggests that temporal gaps between syllables are innate, while syllable morphology is learned.
She added: “The fostered zebra finches sang the Bengalese finch song with a zebra finch accent.”
Neuron activity in the hearing cortex of adult zebra finch brains during exposure to birdsong were also recorded. Results showed that a first set of neurons registered temporal gaps of zebra finch songs, and a separate second set of neurons were responsive to syllable morphology.
The first set of neurons were most sensitive to silent gaps with the same duration as the silent gaps found in natural zebra finch song. But they did not respond if the duration between syllables was too short or too long.
Finally, the team found that each male zebra finch has to develop a unique song that is different from other zebra finches, while maintaining species’ specific identity.
Mind the gap: Neural coding of species identity in birdsong prosody is published in the journal Science.