科学美国人60秒:偷听让焦虑的松鼠感到安心

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 morsels for a lot of different predators."
Keith Tarvin, a behavioral ecologist at Oberlin College. He says squirrels scan their surroundings for hawks and owls, cats and foxes. But they also have another surveillance system: they eavesdrop on nearby birds.
"Eavesdropping on alarm calls or eavesdropping on chatter 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 cognitive 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 hawk.
(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 reassuring 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 subconsciously 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 fabric 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.