Light and odors don't travel well, so it's hard for animals to see or smell.

光和氣味不易被傳遞，所以動物很難目視或嗅聞

But sound moves about four times faster in water than in air,

但是在水中，聲音的傳播速度大約比在空氣中快四倍

so in this dark environment,

因此在這黑暗的環境中 ，

marine mammals often rely on vocalization to communicate.

哺乳類動物經常只靠聲音來溝通，

That's why a chorus of sounds fills the ocean.

這就是海中充滿合唱的原因

Clicks,

喀搭聲、

pulses,

脈衝聲、

whistles,

哨聲、

groans,

沉吟聲、

boings,

彈簧聲、

cries,

哭聲、

and trills, to name a few.

和抖聲等等

But the most famous parts of this underwater symphony

但水中交響樂最著名的部分，

are the evocative melodies, or songs, composed by the world's largest mammals,

就是令人激發聯想的旋律、或是歌聲，出自於世界上最大的哺乳類動物

whales.

鯨魚

Whale songs are one of the most sophisticated communication systems

鯨魚的歌曲是動物王國中最精密的

in the animal kingdom.

溝通系統之一

Only a few species are known to sing.

只有少數物種懂得唱歌

Blue,

藍鯨、

fin,

翅鯨、

bowhead

弓頭鯨、

minke whales,

小鬚鯨、

and of course, humpback whales.

當然，還有座頭鯨

These are all baleen whales

牠們屬於鬚鯨亞目，

which use hairy baleen plates instead of teeth to trap their prey.

使用鯨鬚板代替牙齒捕捉獵物

Meanwhile, toothed whales do use echolocation,

同時，齒鯨會使用回聲定位，

and they and other species of baleen whales

和其他種類的鬚鯨

make social sounds, such as cries and whistles, to communicate.

發出社交聲音來社交，像是哭聲和哨聲來溝通

But those vocalizations lack the complexity of songs.

但這些聲音缺乏樂曲的複雜性

So how do they do it?

所以，牠們是怎麼發聲的呢？

Land mammals like us generate sound by moving air over our vocal cords

人類等陸地哺乳類動物，藉由空氣通過聲帶來發聲

when we exhale, causing them to vibrate.

當我們吐氣時，使聲帶振動發聲

Baleen whales have a U-shaped fold of tissue between their lungs

鬚鯨的肺部之間有Ｕ型摺疊組織，介於肺

and their large inflatable organs called laryngeal sacs.

和大型、可充氣的器官喉囊之間

We don't know this for sure

我們並不確定，

because it's essentially impossible to observe the internal organs

因為基本上我們不可能觀察正在唱歌的鯨魚

of a living, singing whale,

的內部器官

but we think that when a whale sings,

但我們認為當鯨魚唱歌時，

muscular contractions in the throat and chest

喉部和胸腔的肌肉會收縮，

move air from the lungs across the U-fold and into the laryngeal sacs,

讓肺部的空氣通過Ｕ型摺疊組織來到喉囊，

causing the U-fold to vibrate.

震動Ｕ型摺疊組織

The resulting sound resonates in the sacs like a choir singing in a cathedral

最後，聲音在喉囊中共鳴，如同唱詩班在教堂中歌唱，

making songs loud enough to propagate up to thousands of kilometers away.

使聲音大到足以傳播到上千公里外的距離

Whales don't have to exhale to sing.

鯨魚根本不需要呼氣來唱歌

Instead, the air is recycled back into the lungs,

而是將那些空氣循環回肺裡，

creating sound once more.

進而再次發聲

One reason whale songs are so fascinating is their pattern.

鯨歌迷人之處之一在於其樣式，

Units, like moans, cries, and chirps are arranged in phrases.

如沉吟，尖叫、呼喊等單元構成了樂句

Repeated phrases are assembled into themes.

樂句不斷重複，組成主旋律

Multiple themes repeated in a predictable pattern create a song.

多個重複的主旋律，依可預測的樣式組成一曲鯨歌

This hierarchical structure is a kind of grammar.

這種階級式的歌曲架構是一種語法

Whale songs are extremely variable in duration,

鯨歌演唱的時間有長有短，差距甚大

and whales can repeat them over and over.

而鯨魚能不斷地重複歌唱

In one recorded session, a humpback whale sang for 22 hours.

在一個錄音中，一頭座頭鯨連唱了 22 小時

And why do they do it?

那麼牠們為什麼要唱歌呢？

We don't yet know the exact purpose, but we can speculate.

我們不能確定確切的目的，但我們能猜測

Given that the singers are males and they mostly sing during the mating season,

由於唱歌的通常是雄性，而唱歌的時間多半在交配季，

songs might be used to attract females.

唱歌有可能是為了吸引雌性

Or perhaps they're territorial, used to deter other males.

或是牠們保衛領地，驅趕其他雄性

Whales return to the same feeding and breeding grounds annually,

鯨魚每年都會回到同個地點繁殖、哺育後代，

and each discrete population has a different song.

而不同鯨群會有不同歌曲

Songs evolve over time as units or phrases are added, changed, or dropped.

這些歌曲隨時間演化，新增、改變或刪減單元與樂句，

And when males from different populations are feeding within earshot,

當聽力範圍內，不同聚落的雄鯨覓食時，

phrases are often exchanged,

彼此經常會交換樂句

maybe because new songs make them more attractive to breeding females.

也許是新歌對育齡的雌鯨更具吸引力

This is one of the fastest examples of cultural transmission,

這是文化傳播最快速的例子之一，

where learned behaviors are passed between unrelated individuals

習得的行為在同一物種，但無親屬關係的

of the same species.

個體間傳遞

We can eavesdrop on these songs using underwater microphones

我們可以用一種叫做水聽器的水下麥克風

called hydrophones.

偷聽他們唱歌

These help us track species when sightings or genetic samples are rare.

這可以幫助我們追蹤罕見或稀有基因樣本的物種

For example, scientists have been able to differentiate

例如：科學家用鯨歌區別出

the elusive blue whale's populations worldwide based on their songs.

分布於是世界各地的隱匿藍鯨鯨群

But the oceans are getting noisier as a result of human activity.

但海洋因為人類活動日漸吵雜

Boating,

航行、

military sonar,

軍事聲納、

underwater construction,

海底工程

and seismic surveys for oil are occurring more often

和地震探勘原油越來越頻繁，

which may interfere with whale's communication.

這些都可能干擾鯨魚間的溝通

Some whales will avoid key feeding or breeding grounds

有些鯨魚甚至會因為人為噪音太大，

if human noise is too loud.

避開重要覓食地或繁殖地

And humpback whales have been observed to reduce their singing

我們觀察到，座頭鯨會因為 200 公里外的噪音，

in response to noise 200 kilometers away.

減少唱歌的時間

Limiting human activity along migratory routes

在鯨魚遷徙行經的路線上

and in other critical habitats,

和其他重要棲息地限制人為活動，

and reducing noise pollution throughout the ocean

以及降低海中的噪音污染

would help ensure whales continued survival.

可以確保鯨魚繼續生存

If the whales can keep singing and we can keep listening,

如果鯨魚能一直唱歌，我們能一直聆聽，

maybe one day we'll truly understand what they're saying.

或許有一天我們能真正聽懂牠們在說甚麼