These animals can hear everything - Jakob Christensen-Dalsgaard

譯者: Lilian Chiu 審譯者: 麗玲 辛

The world is always abuzz with sounds,

世界總是充滿聲音，

many of which human ears simply can't hear.

其中許多是人耳無法聽到的。

However, other species have extraordinary adaptations

然而，有些物種具有非凡的演化適應，

that grant them access to realms of sonic extremes.

讓牠們能夠進入聲音的極限領域。

And some of them don’t even have ears— at least, not like we typically imagine.

其中有些物種甚至沒有耳朵——

至少不是我們通常想像的那種耳朵。

To understand how the animal kingdom’s best listeners do it,

要了解動物王國的 最佳聆聽者如何做到，

we need to know the rules of their game.

我們就得知道牠們的遊戲規則。

When an object in a medium like air or water moves,

當空氣或水等介質中的物體移動時，

it sends out physical waves.

它會發送出物理波。

The basics of hearing involve structures that vibrate in response to these waves

聽覺的基本原理是： 某些身體結構因為這些波而震動，

and excite sensory cells,

並激發感覺細胞，產生訊號，

generating signals that nerves transmit to the brain,

神經傳遞訊號給大腦， 然後大腦處理訊號。

where they’re processed.

But despite the assemblage of sound-absorbing and -amplifying

但是，儘管我們耳朵中有 吸收和放大聲音的結構設計，

structures in our ears,

many noises are too quiet for us to detect.

許多聲響對我們而言 太小聲了，我們聽不到。

Owls, however, have some workarounds.

然而，貓頭鷹有變通的方法。

Our external ears funnel sounds inward—

我們的外耳會把聲音向內引導——

but many owls use their whole faces to do this.

但許多貓頭鷹會用 整個臉部來做到這一點。

Their ears, hidden beneath a flap of feathers,

牠們的耳朵隱藏在一片羽毛下，

have eardrums proportionally much larger and more sensitive than humans’.

和人類相比，牠們的耳膜 比例大很多，也更敏感。

And because many owls ears are positioned asymmetrically,

且因為許多貓頭鷹的 耳朵位置並不對稱，

sound waves reach them at different times.

聲波抵達的時間也會不同。

This slight delay helps their brains determine the direction

這微小的時差讓牠們的大腦 能夠判定聲音來源的方向。

of the sound’s source.

And great grey owl wings have especially thick velvety coatings

再者，烏林鴞的翅膀有 特別厚實的羽絨覆蓋，

and long feather combs and fringes,

和很長的羽梳及羽緣，

which are thought to help reduce their flight sounds.

一般認為其功能是 減少牠們飛行的聲音。

So, while hovering, they can go undetected

所以，在盤旋時，

牠們可以不被發現，

and concentrate on the subtle sounds of their prey.

並專注於獵物的細微聲音。

這些演化上的改變， 讓烏林鴞可以聽見田鼠

All these adaptations enable a great grey owl to hear a vole

tunneling under 18 inches of snow—

在十八英吋的積雪下挖地道，

and make a fatal strike.

接著發動致命攻擊。

Other animals are almost all ears,

還有幾種動物的耳朵 則佔有很大比例。

like the aptly named long-eared jerboa,

比如名副其實的長耳跳鼠，

which is the animal kingdom’s largest ears in proportion to body length.

其耳朵與體長的比例 是動物王國中最高的。

These sizable sound-collectors help the jerboas sense low frequency noises—

這些大型的收音器讓長耳跳鼠 可以感測到低頻聲音，

and keep cool by radiating heat.

還能散熱以保持涼爽。

Fennec foxes use their large, swiveling ears

大耳狐會用牠可旋轉的大耳朵

to rapidly home in on activity beneath Sahara sands,

來快速鎖定撒哈拉沙漠下的活動，

while bat-eared foxes can pick up savanna sounds

而蝠耳狐可以聽到大草原的聲音，

as slight as termites crawling and munching on grasses.

連白蟻在草上爬行和咀嚼 發出的輕微聲音都聽得見。

Ogre-faced spiders, meanwhile,

至於鬼面蜘蛛，

might not have ears in the traditional vertebrate sense,

牠們也許沒有傳統脊椎動物的耳朵，

but their legs are covered by receptors sensitive to sound waves

但牠們腳上滿是接受器， 能敏感地感測聲波，

as soft as those generated by mosquito flight.

連蚊子飛行所產生的 輕柔聲波都能感測到。

This allows them to catch airborne prey—

這讓牠們能夠捕捉空中的獵物——

even after being blindfolded by scientists.

即使科學家遮住牠們的眼睛， 牠們也能辦到。

Lots of different features also help animal ears hit especially high notes,

還有許多不同的特徵能幫助 動物耳朵接收特別高的音，

like the extra hard, stiff middle ear bones of toothed whales;

比如齒鯨有特別硬的中耳骨，

like dolphins and sperm whales,

比如海豚和抹香鯨，

which efficiently propagate high-frequency vibrations.

能有效地傳播高頻振動。

Indeed, some toothed whales and bats emit sound pulses around 200,000 hertz

甚至有些齒鯨和蝙蝠能發出 約二十萬赫茲的聲脈，

and listen for the reflections.

並聆聽其反射。

These high-frequency wavelengths—

這些高頻波長——比我們能 聽到的頻率還要高十倍以上——

more than 10 times higher than what we can hear—

are small enough to generate strong reflections from objects

小到能夠從極小的物體 產生強力的反射，

as tiny as the insects many bats are after,

這類物體包括許多蝙蝠 在獵捕的昆蟲，

which would be missed altogether by lower ones.

若用較低頻的波長是偵測不到的。

But many insects are also in on the conversation—

但許多昆蟲也會參與對話——

and vigilant to ultrasonic onslaughts.

並對超音波突擊保持警覺。

The greater wax moth can register the highest frequencies

大蠟蛾是記錄中可以感知到 最高頻率的動物——

of any animal recorded— up to 300,000 hertz,

高達三十萬赫茲，

thanks to thin, vibration-sensitive, eardrum-like membranes on their abdomens.

靠的是牠們腹部上 對振動敏感的類耳膜薄膜。

In fact, hearing organs have evolved independently

事實上，在昆蟲中，聽覺器官

已經獨立進化了二十多次。

more than 20 times among insects.

Katydids sense ultrasonic sounds with their front legs;

螽斯用前腳感測超音波聲音；

certain hawkmoths can hear with their mouthparts;

有些天蛾可以用牠們的口器來聆聽；

a parasitic fly registers cricket chirps from organs behind its head;

有一種寄生蠅能用頭部後方的 器官感測到蟋蟀的鳴叫聲；

and the praying mantis has just one hearing organ,

而螳螂只有一個聽覺器官，

which sits smack in the midline of its thorax.

位在其胸部的中線上。

But how low can animals go?

但動物可以聽到多低的頻率？

Well, baleen whales emit sounds around 14 hertz,

鬚鯨發出的聲音約為十四赫茲，

the deepest among mammals.

是哺乳類中最深沉的聲音。

These vibrations can travel thousands of kilometers.

這種振動可以傳到數千公里外，

And they get picked up by other baleen whales—

且會被其他的鬚鯨接收到——

possibly via their skulls,

牠們可能是用頭骨來接收，

which conduct the vibrations along to their ear bones.

頭骨能把振動傳導到耳骨。

Snakes pick up ground vibrations by way of their jawbones,

蛇類用牠們的下顎骨 來感測地面的振動，

which connect directly to their middle ear bones.

牠們的下顎骨直接連結到中耳骨。

And Namib Desert golden moles regularly stick their heads into the sand,

納米布沙漠金毛鼴鼠

經常把牠們的頭埋入沙中，

which likely helps them use their large, club-like middle ear bones

這可能有助於牠們使用 牠們的棍棒狀大型中耳骨，

to sense low frequency activity in mounds more than 20 meters away.

去感測二十公尺外 土丘中的低頻活動。

So, odds are: if a tree falls in a forest, someone’s bound to hear it.

所以，很有可能：

如果森林中有棵樹倒下， 一定會有某人（動物）聽見。