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This is Scientific American's 60-second Science, I'm Christopher Intagliata.

Seems like any time you see a squirrel, it's busy doing something—headed somewhere; scrounging for food. And being out and about all the time also means "they're tasty morsels¹ for a lot of different predators²."

Keith Tarvin, a behavioral ecologist at Oberlin College. He says squirrels scan their surroundings for hawks⁴ and owls⁵, cats and foxes. But they also have another surveillance system: they eavesdrop⁶ on nearby birds.

"Eavesdropping⁷ on alarm calls or eavesdropping on chatter⁸ is a cheap and easy way to supplement the information they have access to. Because it's free. It's produced by other individuals in the environment. It's publicly available to any organism that has the cognitive⁹ ability to recognize and interpret that information."

Tarvin's colleague Marie Lilly tested that ability by riding round town on her bicycle, stopping when she found a squirrel. Then she'd set up her equipment. Play the fearsome scream of a red-tailed hawk³.

(CLIP: Hawk sound)

And then either play the casual, unworried chatter of songbirds...

(CLIP: Chatter)

... or ambient noise...

(CLIP: Ambient)

... as a control. All the while, she observed the squirrels' behavior.

And she noticed that when squirrels heard the reassuring¹⁰ chatter of songbirds following the hawk's scream, they relaxed more readily. "Imagine this: If you're walking in a crowd, and everyone seems pretty happy and content, and they're chitchatting with each other, you might even subconsciously¹¹ take that as information that all of those eyes and ears perceive the environment as being safe. And we think the squirrels might be listening in on bird chatter in the same way." The details are in the journal PLOS ONE.

Squirrels give back to the community, too, with their own alarm calls.

(CLIP: Squirrel alarm)

Which might help other eavesdropping animals. But in busy urban environments, Tarvin says that rich fabric¹² of animal communication risks being drowned out, by the loudest animals around: us.

(CLIP: City sounds)

Thanks for listening for Scientific American — 60-Second Science. I'm Christopher Intagliata.

这里是科学美国人——60秒科学系列，我是克里斯托弗·因塔格里塔。

好像任何时候看到松鼠，它们都在忙碌——忙着前往某地或是寻找食物。一直四处奔波意味着“它们是许多不同捕食者眼中的可口食物。”

奥伯林学院的行为生态学家基思·塔文说到。他表示，松鼠会察看周围是否有鹰、猫头鹰、猫和狐狸。不过它们还有另外一个监视系统：它们会窃听附近的鸟类。

“窃听鸟类警报声或鸣叫声是一种廉价且简单的方式，可以补充它们获得的信息。因为这些信息是免费得到的。是由环境中的其它个体产生的。任何具有识别能力且能解释这些信息的生物都能公开获取。”

塔文的同事玛丽·莉莉测试了这种能力，她骑着自行车环绕城镇，发现松鼠就停下。然后，她架起自已的设备。播放红尾鵟可怕的尖叫声。

（片段：鹰叫声）

然后再播放鸣鸟轻松且无忧无虑的鸣叫声

（片段：鸣叫声）

或是环境噪声

（片段：环境音）

作为对照。期间她一直在观察松鼠的行为。

她注意到，在听到红尾鵟的尖叫之后又听到鸣鸟的鸣叫声时，松鼠会更容易放松下来。“想象一下，假如你走在人群中，所有人都看起来很开心而且很满足，他们在彼此聊着天，你甚至可能下意识地将其视为‘所有人都认为环境很安全'的信息。我们认为松鼠可能会以同样的方式偷听鸟类的鸣叫声。”研究详情刊登在《公共科学图书馆·综合》期刊上。

松鼠也会用自已的警报声回馈群体。

（片段：松鼠警报声）

这可能有助于其它偷听动物。但塔文表示，在繁忙的城市环境中，动物丰富的交流结构有被周围最吵闹动物盖过的风险，这种最吵闹的动物就是我们人类。

（片段：城市的声音）

谢谢大家收听科学美国人——60秒科学。我是克里斯托弗·因塔利亚塔。