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  • This is a song sung by a brown thrasher.

  • But that's just one of the thousand or more that it knows,

  • and it's not the only avian virtuoso.

  • A wood thrush can sing two pitches at once.

  • A mockingbird can match the sounds around it, including car alarms.

  • And the Australian superb lyrebird

  • has an incredible, elaborate song and dance ritual.

  • These are just a few of the 4,000 species of songbirds.

  • Most birds produce short, simple calls,

  • but songbirds also have a repertoire of complex vocal patterns

  • that help them attract mates,

  • defend territory,

  • and strengthen their social bonds.

  • Each songbird species has its own distinct song patterns,

  • some with characteristic regional dialects.

  • Experienced listeners can even distinguish individual birds by their unique songs.

  • So how do birds learn these songs in the first place?

  • How do they know to mimic the songs of their own species?

  • Are they born knowing how to sing?

  • A lot of what scientists know about bird song comes from studying zebra finches.

  • A baby male zebra finch typically learns to sing from its father or other males,

  • starting while it's still a fledgling in the nest.

  • First comes a sensory learning phase,

  • when the baby finch hears the songs sung around it and commits them to memory.

  • The bird starts to vocalize during the motor learning phase,

  • practicing until it can match the song it memorized.

  • As the bird learns, hearing the tutor's song over and over again

  • is helpfulup to a point.

  • If he hears it too many times, the imitation degrades

  • and the source matters.

  • If the song is played through a loudspeaker,

  • he can't pick it up as easily.

  • But hide the same loudspeaker inside a toy painted to look like a zebra finch,

  • and his learning improves.

  • What if the baby never hears another zebra finch's song?

  • Interestingly enough, it'll sing anyway.

  • Isolated finches still produce what are called innate or isolate songs.

  • A specific tune might be taught,

  • but the instinct to sing seems to be hardwired into a songbird's brain.

  • Innate songs sound different from theculturedsongs

  • learned from other finchesat first.

  • If isolated zebra finches start a new colony,

  • the young birds pick up the isolate song from their parents.

  • But the song changes from generation to generation.

  • And after a few iterations,

  • the melody actually starts to resemble

  • the cultured songs sung by zebra finches in the wild.

  • Something about the learning process must be hardwired, too,

  • drawing the birds towards the same song patterns again and again.

  • This means that basic information about the zebra finch song

  • must be stored somewhere in its genome,

  • imprinted there by millions of years of evolution.

  • At first, this might seem odd,

  • as we usually think of genetic code as a source of biochemical or physical traits,

  • not something like a behavior or action.

  • But the two aren't fundamentally different;

  • we can connect genomes to behavior through brain circuitry.

  • The connection is noisy and quite complex.

  • It doesn't simply map single genes to single behaviors, but it exists.

  • Genomes contain codes for proteins that guide brain development,

  • such as molecules that guide the pathways of developing axons,

  • shaping distinct circuits.

  • Birds' brains have so-calledsong circuits

  • that are active when the birds sing.

  • These circuits also respond to the song of a bird's own species

  • more strongly than to other species' songs.

  • So the theory is that a bird's genes guide development of brain circuits

  • that relate to singing and the ability to learn songs.

  • Then, exposure to songs shapes those neural circuits

  • to produce the songs that are typical to that species.

  • Genetically encoded or innate behaviors aren't unique to songbirds.

  • They're widespread in the animal kingdom.

  • Spectacular examples include

  • the long-distance migrations of monarch butterflies and salmon.

  • So what does this mean for humans?

  • Are we also born with innate information written into our genomes

  • that helps shape our neural circuits,

  • and ultimately results in something we know?

  • Could there be some knowledge

  • that is unique and intrinsic to humans as a species?

This is a song sung by a brown thrasher.

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B2 US TED-Ed zebra finch innate bird hears

【TED-Ed】How do birds learn to sing? - Partha P. Mitra

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    IS LIU posted on 2018/04/07
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