Whales Use Song as Sonar鯨魚以歌聲為聲吶

伯特·甘比尼

Any quick Internet search for recordings of humpback whale song returns audio compilations that can receive tens of thousands， if not millions， of visits.

With such quantifiable popularity， you might ask， “Who doesn’t love listening to whale song？” One surprising answer might be， “whales，” according to an intriguing model developed by a University at Buffalo researcher.

It’s not that listening whales ignore the singers of their species. The question for Eduardo Mercado III， a professor in UB’s Department of Psychology， is how humpback whales perceive the song， which is among the most sophisticated acoustic performances in the animal kingdom.

Mercado has published a paper in the journal Frontiers in Psychology that hypothesizes whale song helps singers perform a type of auditory scene analysis.

He’s not the first researcher to suggest the idea of humpbacks using sonar， but he’s probably the first to analyze the possibility that songs might be used for sonar.

Mercado’s model proposes that the sender is also the receiver. He says whale song provides useful information to the singing whale， not just listening whales.

“Nearly every biologist is going to say this is nonsense， but I still maintain the direction of the current scientific consensus is wrong，” says Mercado. “Assuming whales hear the songs as beautiful displays like a human might is imposing our perception on theirs.”

“What are the whales perceiving？” he asks. “Scientifically， we have to consider that.”

The current assumption has remained for decades that whales sing predominantly for reproductive purposes， using their song as sexual signals that provide a way for females to find high-quality males; for males to attract females; or for males to compete with other males.

That’s the scene for the biologist. In each case， the listening whale would be doing most of the song analysis.

But Mercado says the evidence collected so far provides little support for the sexual advertisement hypothesis.

In his view， the data points more toward it being the singer， not the listener， who is doing most of the analysis through echolocation.

Mercado says humpbacks sing as a way to explore their world.

The goal is still predominantly reproductive， but the song in this case is a like a searchlight that informs singers about the presence of other whales， the direction those whales might be heading and whether or not the singer might be able to catch up to them.

“That’s why they’re singing，” he says. “They’re trying to create a scene that would not be there otherwise. When they create these echoes it’s like shining a searchlight in the dark.”

Mercado began to develop his model by examining the physics of the problem.

To create a simplified version of what would need to happen for echolocation to work he started asking questions： How could this work？ What echoes might come back to singers？ How strong would they be？ Could they be resolved from other sounds？ And what information could they provide？

“The model suggests that singers could easily obtain information about the location of other whales，” he says.

As a graduate student， Mercado accepted a job analyzing whale song. But much of what he heard didn’t make sense. For instance， the library of sound used by whales was changing in different years， demanding whales process new songs every year.

“That’s more difficult than humans trying to annually learn a new language，” says Mercado. “For whales， it isn’t just language， but a whole new range of sounds and new patterns of sounds.”

“For us， it would be like trying to communicate with a new species of humans with different vocal chords that produce a radically different language.”

This apparent learning ability is what interested Mercado， an expert on the effects of learning on brain function， in humpback whale song.

“If my hypothesis is valid it means that whales are doing something much more complicated than what humans can even begin to approach，” he says. “If we understood how whales accomplish this， it could help us understand better how brains work in general.”

Mercado understands why researchers would be skeptical about his model， but he says it’s a testable hypothesis.

If he’s right， Mercado says it should change the direction of how we study whales.

“It’s easy to get locked into believing something that seems obvious. But looks， or in this case， sounds， can be deceiving，” he says. “Right now， whale song is being analyzed in a way that might not be accurate.”

在互聯(lián)網(wǎng)上快速搜索座頭鯨的歌聲錄音，每次都能搜到不少的音頻選輯，訪問量沒有數(shù)百萬也有數(shù)萬。

這種可量化的人氣也許會讓你好奇發(fā)問：“誰不愛聽鯨魚的歌？”紐約州立大學(xué)布法羅分校的一名研究員開發(fā)出一個有趣的模型，該模型給出了一個令人意想不到的答案——鯨魚。

這并不是說聽歌的鯨魚對其種群中的歌唱者不予理睬。布法羅分校心理學(xué)系教授愛德華多·默卡多三世所關(guān)注的問題是，座頭鯨如何感知歌聲。鯨魚歌唱可是動物界最復(fù)雜的聲學(xué)表演之一。

默卡多在《心理學(xué)前沿》雜志上發(fā)表了一篇論文，他在文中提出一種假說——唱歌的鯨魚可以借助歌聲來完成一種聽覺場景分析。

默卡多不是第一個提出座頭鯨使用聲吶的研究者，但他很可能是第一個分析座頭鯨能將其歌聲用作聲吶的人。

默卡多的模型提出，發(fā)聲者同時也是聽聲者。他認(rèn)為，鯨魚的歌聲不僅將有用的信息提供給聽歌的鯨魚，也提供給唱歌的鯨魚自己。

“幾乎每一位生物學(xué)家都會認(rèn)為我在胡說八道，但我堅信目前科學(xué)界的共識在方向上出了錯?！蹦ǘ啾硎荆八麄冋J(rèn)為鯨魚就像人類一樣，大概是在欣賞歌聲之美，這是把人類的感知強(qiáng)加給它們。”

“鯨魚在感知些什么呢？”他問道，“科學(xué)上，我們必須思考這個問題?！?/p>

幾十年來，人們一直認(rèn)為鯨魚歌唱主要是為了繁殖目的，它們用歌聲傳遞求偶信號，雌鯨借以尋找優(yōu)質(zhì)雄鯨，雄鯨則以此吸引雌鯨或與其他雄鯨競爭。

這就是生物學(xué)家眼中的場景。在每種情況下，都是聽歌的鯨魚做大部分的歌聲分析工作。

但默卡多指出，目前為止收集到的證據(jù)幾乎無法支撐上述的求偶宣傳假說。

在他看來，資料更能證明的是，通過回聲定位進(jìn)行大多數(shù)分析工作的是歌唱者，而非聽歌者。

默卡多表示，座頭鯨以歌唱作為探索世界的一種方式。

它們唱歌的目的主要還是為了繁殖，但這種情況下，歌聲就像一盞探照燈，告知歌唱者其他鯨魚的存在、它們可能的前進(jìn)方向，以及自己能否趕上它們。

“這就是它們唱歌的原因?！彼f，“它們正在試圖創(chuàng)造一個只有唱歌才會出現(xiàn)的場景。它們創(chuàng)造回聲就像在黑暗中點(diǎn)亮一盞探照燈?！?/p>

默卡多開始通過探查問題的原理來建立模型。

為了簡化回聲定位起作用的相關(guān)條件，他開始追問：這是如何起作用的？哪些回聲會反饋給歌唱者？這些回聲有多強(qiáng)？能否將回聲與其他聲音區(qū)別開？它們能提供什么樣的信息？

他說：“模型顯示，唱歌的鯨魚能輕易獲知其他鯨魚的位置信息?！?/p>

讀研究生時，默卡多接受了一份分析鯨魚歌聲的工作。不過，他聽到的大多數(shù)歌聲都毫無意義。比如，不同的年份，鯨魚使用的聲音數(shù)據(jù)一直在變，要求它們每年要加工新歌。

“這比人類每年都嘗試學(xué)習(xí)一門新語言更難。”默卡多說，“對鯨魚來說，要加工處理的不單是語言，而是一套全新的聲音和新的聲音模式?！?/p>

“對我們來說，這就像是試圖與一個新人種進(jìn)行交流，這個新人種的聲帶與我們有別，說出的語言也與我們截然不同。”

默卡多的專長是研究學(xué)習(xí)對大腦功能產(chǎn)生的影響，正是座頭鯨歌聲中體現(xiàn)出的這種顯見的學(xué)習(xí)能力引起了他的興趣。

“如果我的假設(shè)成立，這意味著鯨魚所做的事情遠(yuǎn)比人類所能企及的復(fù)雜得多?！彼f，“如果我們明白了鯨魚是如何做到的，這將幫助我們更好地理解大腦普遍的工作機(jī)理。”

默卡多明白為什么研究人員會對他的模型持懷疑態(tài)度，但他說這是一個可驗(yàn)證的假設(shè)。

默卡多說，如果他是對的，這應(yīng)該會改變我們研究鯨魚的方向。

“人們很容易堅信一些看似顯而易見的事情。但外表，或我們這里說的聲音，可能有欺騙性?！彼f，“當(dāng)下，人們研究鯨魚歌聲的方式或許并不準(zhǔn)確?！?/p>

（譯者單位：江西師范大學(xué)）