The surprising reason birds sing - Partha P. Mitra

譯者: Marssi Draw 審譯者: Regina Chu

【影片中有在野外錄製的鳥鳴聲 建議您戴上耳機收聽】

這首歌是褐噪鶇唱的

This is a song sung by a brown thrasher.

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

但牠會唱的不只這一首，還有上千首

and it’s not the only avian virtuoso.

而且牠不是唯一的鳥唱將

A wood thrush can sing two pitches at once.

黃褐森鶇可以同時唱出兩種音高

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

小嘲鶇可以發出周遭環境出現的聲音

包含汽車防盜警報聲

And the Australian superb lyrebird

澳洲的華麗琴鳥

has an incredible, elaborate song and dance ritual.

有超級繁複的歌舞儀式

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

這些鳥只是四千多種 鳴鳥之中的幾種而已

Most birds produce short, simple calls,

大部分的鳥類都可以發出簡單的短音

but songbirds also have a repertoire of complex vocal patterns

但鳴鳥還能唱出整套複雜的音調

that help them attract mates,

幫牠們求偶

defend territory,

捍衛地盤

and strengthen their social bonds.

還能擴展社交圈

Each songbird species has its own distinct song patterns,

每種鳴鳥都有獨一無二的曲調

some with characteristic regional dialects.

部分還帶有特殊方言

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

經驗老道的高手甚至能 透過獨特的歌曲分辨出是哪種鳥在唱歌

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

究竟鳥類是怎麼學這些歌的？

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

牠們怎麼知道要模仿同類鳥唱歌？

Are they born knowing how to sing?

牠們生來就會唱歌嗎？

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

科學家所知的鳥類歌曲 大部分來自對斑胸草雀的研究

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

基本上斑胸草雀雄寶寶 向牠的父親或其他雄鳥學唱歌

starting while it’s still a fledgling in the nest.

而且在牠還在鳥巢裡 學飛的時候就開始了

First comes a sensory learning phase,

首先是感覺學習階段

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

雀寶寶會聽到、記住 在牠身邊吟唱的歌曲

The bird starts to vocalize during the motor learning phase,

然後在動作學習階段開始發聲

practicing until it can match the song it memorized.

一直練到能完整唱出記憶中的歌曲

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

小鳥學習時會一再重覆聆聽師父唱歌

is helpful— up to a point.

這招在某個程度上很有用

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

但是聽太多次，牠的模仿力就會降低

and the source matters.

此時聲音的來源就很重要

If the song is played through a loudspeaker,

如果歌曲是透過喇叭播放

he can’t pick it up as easily.

小鳥就沒辦法輕易學成

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

但如果把同樣的音響 藏在斑胸草雀的玩偶裡面

and his learning improves.

牠就會進步

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

要是寶寶沒聽過其他 斑胸草雀唱歌會怎麼樣呢？

Interestingly enough, it’ll sing anyway.

有趣的是，牠們還是會唱歌

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

被隔離的雀還是能唱出 所謂天生或與世隔絕的歌曲

A specific tune might be taught,

小鳥可能會學一種特定的音調

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

但唱歌的天性似乎 內建在鳴鳥的大腦裡

Innate songs sound different from the “cultured” songs

天生會唱的歌一開始聽起來

learned from other finches—at first.

和從其他雀那裡學來的不一樣

If isolated zebra finches start a new colony,

如果一隻被隔離的雀開始建立新地盤

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

幼鳥從父母那學會唱與世隔絕歌

But the song changes from generation to generation.

但歌會隨著世代而改變

And after a few iterations,

重覆幾次之後

the melody actually starts to resemble

旋律會開始變得像

the cultured songs sung by zebra finches in the wild.

斑胸草雀在野外傳唱的那些歌曲

Something about the learning process must be hardwired, too,

學習唱歌的方法也是內建的

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

讓鳥類一再朝唱相同曲調的方向前進

This means that basic information about the zebra finch song

這表示斑胸草雀歌曲的基本資訊

must be stored somewhere in its genome,

一定儲存在牠們的基因組裡面

imprinted there by millions of years of evolution.

經過百萬年的進化烙印其中

At first, this might seem odd,

乍聽之下可能有點奇怪

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

畢竟通常我們想到的基因密碼 是生化或生理特徵的來源

not something like a behavior or action.

而非行為舉止特徵的來源

But the two aren’t fundamentally different;

但這兩類並非毫不相干

we can connect genomes to behavior through brain circuitry.

我們可以經由大腦迴路 把基因組和行為組合起來

The connection is noisy and quite complex.

這之間的連結頗為複雜難解

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

不是單一基因標示單一行為這麼單純

但連結確實存在

Genomes contain codes for proteins that guide brain development,

基因組裡有代碼 讓蛋白質引導大腦發育

such as molecules that guide the pathways of developing axons,

例如引導發展中軸突路徑的分子

shaping distinct circuits.

會塑造獨特的迴路

Birds’ brains have so-called “song circuits”

鳥類的大腦有所謂的「歌曲迴路」

that are active when the birds sing.

在鳥類唱歌的時候會變得活躍

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

這些迴路對同種鳥類的歌曲

more strongly than to other species’ songs.

會比其他鳥類的歌曲 產生更強烈的反應

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

理論上，鳥的基因會引導大腦中

that relate to singing and the ability to learn songs.

與唱歌和學歌能力相關迴路的發展

Then, exposure to songs shapes those neural circuits

之後，聽到歌曲會形塑那些神經廻路

to produce the songs that are typical to that species.

進而產生出同種鳥類的典型歌曲

Genetically encoded or innate behaviors aren’t unique to songbirds.

基因編碼或天生行為並非鳴鳥獨有

They’re widespread in the animal kingdom.

在動物王國裡十分普遍

Spectacular examples include

格外非凡的案例還有

the long-distance migrations of monarch butterflies and salmon.

長途遷徙的帝王蝶和鮭魚

So what does this mean for humans?

這對人類來說有什麼意義？

Are we also born with innate information written into our genomes

我們也生來就有某種 訊息存在基因組裡

that helps shape our neural circuits,

幫助我們形塑神經迴路

and ultimately results in something we know?

最後造成某種我們已知的特質嗎？

Could there be some knowledge

有沒有可能某種知識

that is unique and intrinsic to humans as a species?

是獨一無二內建在人類之中？