Crows can count vocally like toddlers, research shows

AILSA CHANG, HOST:

Math - regardless of how you feel about the subject, most of us have mastered the basics at an early age. For instance, toddlers know how to count. But, you know, we now know that counting isn't just a human thing. Crows count, too, and they can do it out loud. Here's science reporter Ari Daniel.

ARI DANIEL, BYLINE: Let's say I put three blocks in front of a young toddler. Instead of counting one, two, three, they might say one, one, one. Each word refers to one of the blocks, adding up to three. This is an early form of counting, says Diana Liao, a neuroscientist at the University of Tubingen in Germany.

DIANA LIAO: Toddlers learning to count - they use the number words as verbal tallies.

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DANIEL: The child's keeping track of a quantity of things - in this case, three - by producing a sound again and again and again.

LIAO: A couple months later, the toddler will just respond with three. So it's this developmental stage of learning to count.

DANIEL: That one-one-one form of counting requires a toddler to be able to both tally each object with a sound and control the number of sounds they're making. Liao wanted to know whether this second ability of producing a specific number of sounds is something that other animals can do. Her critter of choice - the carrion crow.

LIAO: Crows are great. They're super smart, so they're a lot of fun to work with.

DANIEL: Liao enrolled three male birds from the university's aviary. First, she trained them to produce a different number of calls - one, two, three or four - in response to four random visual cues and also to four random sounds...

LIAO: ...A guitar chord...

(SOUNDBITE OF GUITAR CHORD)

LIAO: ...A drumroll...

(SOUNDBITE OF DRUMROLL)

LIAO: ...A cash register noise...

(SOUNDBITE OF CASH REGISTER OPENING)

LIAO: ...And, I think, a frequency sweep.

(SOUNDBITE OF HIGH-PITCHED TONE)

DANIEL: If they responded correctly, they got a food reward. If not, they got a time out. It didn't take long for the crows to catch on - or so Liao thought.

LIAO: I was like, wow, these crows are brilliant. And then I realized they were actually adopting the simpler strategy of just vocalizing until I get a reward (laughter).

DANIEL: So Liao pivoted. She trained them to call a certain number of times, stop and then peck a screen to report their final answer - no cheating. This time, the crows pretty much nailed it. But even when they made a mistake, their wrong answers still tended to hover around the right number.

LIAO: It's, like, easier to confuse three and four, as opposed to, for example, one and four.

DANIEL: Before the crows responded to the signal, they took a bit of time to react. Have a listen.

(SOUNDBITE OF CROW CALLING FOUR TIMES)

DANIEL: The greater the number of calls they had to make, the longer the reaction time. Liao interprets that as a sign the crows were perhaps planning their answer before they began to call. She and her colleagues conclude these birds can indeed control the number of calls they produce.

LIAO: We show that crows have the capacity to count vocally, which mirrors this important developmental stage in toddlers.

DANIEL: The results are published in the journal Science. Chris Templeton is a biologist at Western Washington University who wasn't involved in the research.

CHRIS TEMPLETON: Maybe these crows are able to really intentionally produce vocalizations, and they have this idea of what their vocalizations mean.

DANIEL: Templeton has studied chickadees. He's found that the more dangerous a predator is, the more dee sounds the birds insert into their calls. This...

(SOUNDBITE OF CHICKADEE CALLING WITH FIVE DEES)

DANIEL: ...Versus this...

(SOUNDBITE OF CHICKADEE CALLING WITH THREE DEES)

DANIEL: Templeton isn't sure what's driving that difference, but he says the new research suggests that chickadees may be deciding how many dees to make and then counting them as they make them. Now, Templeton does point out that we humans aren't necessarily the benchmark of all animal intelligence.

TEMPLETON: Animals are smart in a whole bunch of different ways, and those may or may not be the same things that we do.

DANIEL: Meaning if crows were to give us an intelligence test, we may not pass. It's something we can almost certainly count on.

For NPR News, I'm Ari Daniel.

(SOUNDBITE OF COUNTING CROWS SONG, "MR. JONES") Transcript provided by NPR, Copyright NPR.