These animals can hear everything - Jakob Christensen-Dalsgaard

翻译人员: Liwen Huang 校对人员: Lexi Ding

The world is always abuzz with sounds,

世界充斥着各种声音，

many of which human ears simply can't hear.

其中许多声音人耳根本听不见。

However, other species have extraordinary adaptations

但是，其他物种具有 非凡的适应能力，

that grant them access to realms of sonic extremes.

这使它们能够听到极限声波。

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

而且它们中有些甚至没有耳朵—— 至少耳朵长得和我们所想的不一样。

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

要弄清楚那些动物的听力 为什么那么好，

we need to know the rules of their game.

我们需要先了解声音传播的原理。

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

当物体在空气或水等介质中移动时，

it sends out physical waves.

它会发出物理波。

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

听觉的基本原理是， 听觉结构会随着这些波而振动，

and excite sensory cells,

并刺激感觉细胞，

generating signals that nerves transmit to the brain,

产生信号的由神经传递到大脑，

where they’re processed.

再由大脑进行处理。

But despite the assemblage of sound-absorbing and -amplifying

尽管我们的耳朵里

structures in our ears,

有吸音和扩音的结构

many noises are too quiet for us to detect.

许多声音对我们而言 还是轻得无法察觉。

Owls, however, have some workarounds.

不过，猫头鹰可不一样。

Our external ears funnel sounds inward—

我们的外耳似漏斗，向内聚集声音，

but many owls use their whole faces to do this.

而许多猫头鹰用整张脸来聚集声音。

Their ears, hidden beneath a flap of feathers,

它们的耳朵隐藏在羽毛之下，

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

耳膜比人类的大得多，也灵敏得多。

And because many owls ears are positioned asymmetrically,

而且许多猫头鹰的耳朵位置不对称，

sound waves reach them at different times.

因此两只耳朵收到声波的时间不同。

This slight delay helps their brains determine the direction

这种轻微的延迟有助于它们的大脑

of the sound’s source.

确定声源的方向。

And great grey owl wings have especially thick velvety coatings

大灰林鸮翅膀上覆盖着特别厚的、 天鹅绒般柔软的绒羽

and long feather combs and fringes,

以及长长的飞羽和羽缘，

which are thought to help reduce their flight sounds.

据说有助于降低它们飞行的声音。

So, while hovering, they can go undetected

因此，在天空盘旋时， 它们可以不被发现，

and concentrate on the subtle sounds of their prey.

只专注于猎物的细微动静。

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

这些适应性变化使大灰林鸮能够听到

tunneling under 18 inches of snow—

田鼠在 18 英寸的积雪下 挖地道的声音——

and make a fatal strike.

然后进行致命一击。

Other animals are almost all ears,

有些动物几乎全身都是耳朵，

like the aptly named long-eared jerboa,

比如名字很贴切的长耳跳鼠，

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

相对于身长而言， 它是动物界耳朵最大的。

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

这对大耳朵帮跳鼠感知低频声音——

and keep cool by radiating heat.

并通过散热保持凉爽。

Fennec foxes use their large, swiveling ears

耳廓狐靠它们摇摇摆摆的大耳朵

to rapidly home in on activity beneath Sahara sands,

快速地捕捉撒哈拉沙漠下的动静，

while bat-eared foxes can pick up savanna sounds

而蝠耳狐则能捕捉到草原上

as slight as termites crawling and munching on grasses.

白蚁爬行和啃食青草的轻微声音。

Ogre-faced spiders, meanwhile,

与此同时，食人魔脸蜘蛛

might not have ears in the traditional vertebrate sense,

或许没有传统脊椎动物意义上的耳朵，

but their legs are covered by receptors sensitive to sound waves

但它们的腿上布满了感受器，

as soft as those generated by mosquito flight.

对轻如蚊子飞行产生的声波都很敏感。

This allows them to catch airborne prey—

这使它们能够捕捉空中的猎物——

even after being blindfolded by scientists.

即使被科学家蒙住眼睛。

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

许多不同的特征还可以帮助 动物的耳朵听到特别高的音调，

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

例如齿鲸类动物格外坚硬的中耳骨；

like dolphins and sperm whales,

像海豚和抹香鲸的中耳骨

which efficiently propagate high-frequency vibrations.

就可以有效地传播高频振动。

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

事实上，一些齿鲸和蝙蝠会发出 高达 20 万赫兹左右的声脉冲，

and listen for the reflections.

然后倾听回声。

These high-frequency wavelengths—

这些高频波长——

more than 10 times higher than what we can hear—

比我们能听到的波长 高出 10 多倍——

are small enough to generate strong reflections from objects

小到足以使许多微小物体，

as tiny as the insects many bats are after,

比如蝙蝠正在捕食的昆虫等 产生强烈的反射，

which would be missed altogether by lower ones.

而低频波长则会完全错过这些反射。

But many insects are also in on the conversation—

但是许多昆虫也能捕获高频声波，

and vigilant to ultrasonic onslaughts.

并对超声波攻击保持警惕。

The greater wax moth can register the highest frequencies

在有记录的动物中， 大蜡蛾能听到最高的频率——

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

高达 30 万赫兹，

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

这归功于它们腹部有一层薄薄的、 对振动敏感的、像耳膜一样的薄膜。

In fact, hearing organs have evolved independently

实际上，昆虫的听觉器官

more than 20 times among insects.

已经独立进化了 20 多次。

Katydids sense ultrasonic sounds with their front legs;

蝈蝈儿用前腿感知超声波；

certain hawkmoths can hear with their mouthparts;

某些天蛾可以用口器听声音；

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

寄生蝇用头后面的器官 听到蟋蟀唧唧叫；

and the praying mantis has just one hearing organ,

螳螂只有一个听觉器官，

which sits smack in the midline of its thorax.

就在它胸部的中线上。

But how low can animals go?

但是动物能发出多低的声音呢？

Well, baleen whales emit sounds around 14 hertz,

须鲸发出的声音约为 14 赫兹，

the deepest among mammals.

是哺乳动物中最低沉的。

These vibrations can travel thousands of kilometers.

这些振动可以传播数千公里。

And they get picked up by other baleen whales—

然后被其它须鲸捕捉到——

possibly via their skulls,

可能是通过它们的头骨，

which conduct the vibrations along to their ear bones.

将振动传到耳骨。

Snakes pick up ground vibrations by way of their jawbones,

蛇类通过颌骨接收地面振动，

which connect directly to their middle ear bones.

颌骨直接与中耳骨相连。

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

纳米布沙漠的金鼹鼠 经常把头埋到沙子里，

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

这很可能有助于它们 用巨大的棍棒状中耳骨

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

来感知 20 多米外 沙堆中的低频活动。

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

因此，如果森林里有树倒下， 一定会有人听到。