One Caw, Two Caws …

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Carrion crows are not known for their beauty or love of song.

But they have more than their share of smarts.

Now, researchers have figured out that these birds can vocally count to four, according to a new study published in Science.

“Our results show that humans are not the only ones who can do this,” said lead author Andreas Nieder of the University of Tübingen in Germany in a statement. “In principle it also opens up sophisticated communication to the crows.”

These birds are known for their formidable learning ability, the authors of the study wrote. Earlier studies have already shown that the birds understand counting and have very good vocal control.

To see if the crows could go further, researchers conducted experiments with three carrion crows to see whether they could apply these abilities in combination by training them to respond to specific sounds and visual cues: For instance, a frequency sound required four caws, a drum roll three, a cash register klang two, and a guitar chord one.

In visual tests, the birds saw Arabic numerals on a screen and had to vocalize the corresponding number in caws. The birds would then tap the screen to indicate they were done and received mealworms as rewards for correctly counting.

The team came across some interesting findings: The crows were most accurate when vocalizing lower numbers, such as a 100 percent accuracy rate at counting one. That accuracy dropped to 50 percent when counting three and fell to 40 percent with four caws – the latter sometimes even annoying them to the point of refusing to count.

This reluctance and the longer reaction times for higher numbers suggest the crows engaged in mental planning before vocalization, explained Nieder.

“This indicates that, from the information presented to them, the crows form an abstract numerical concept which they use to plan their vocalizations before emitting the calls,” he said in a statement.

The study contributes to the body of work on how certain bird species can communicate numerical information.

A 2005 study on black-capped chickadees found that these birds adjust the number of “dee” sounds in their alarm calls based on predator size.

The authors are now planning to explore how crows might use their counting ability in natural settings, and identify which brain regions are involved.

“The avian lineage diverged from the primate lineage over 300 million years ago,” co-author Diana Liao told Popular Science. “It would be fascinating to see how different brains come up with similar behaviors.”