These crows have counting skills previously only seen in people

These crows have counting skills previously only seen in people

The corvids are the first animals other than humans known to produce a deliberate number of calls on command.
  1. Mariana Lenharo
    1. Mariana Lenharo is a news reporter for Nature based in New York City.
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Crows have dazzled scientists with their ability to count their calls.Credit: John Eveson/Alamy

Crows know their numbers. An experiment has revealed that these birds can count their own calls, showcasing a numerical skill previously only seen in people.

Investigating how animals understand numbers can help scientists to explore the biological origins of humanity's numerical abilities, says Giorgio Vallortigara, a neuroscientist at the University of Trento in Rovereto, Italy. Being able to produce a deliberate number of vocalizations on cue, as the birds in the experiment did, "is actually a very impressive achievement", he notes.

Andreas Nieder, an animal physiologist at the University of Tübingen in Germany and a co-author of the study published 23 May in Science1, says it was amazing to see how cognitively flexible these corvids are. "They have a reputation of being very smart and intelligent, and they proved this once again."

A murder of one

The researchers worked with three carrion crows ( Corvus corone) that had already been trained to caw on command. Over the next several months, the birds were taught to associate visual cues — a screen showing the digits 1, 2, 3 or 4 — with the number of calls they were supposed to produce. They were later also introduced to four auditory cues that were each associated with a distinct number.

During the experiment, the birds stood in front of the screen and were presented with a visual or auditory cue. They were expected to produce the number of vocalizations associated with the cue and to peck at an 'enter key' on the touchscreen monitor when they were done. If they got it right, an automated feeder delivered bird-seed pellets and mealworms as a reward.

They were correct most of the time. "Their performance was way beyond chance and highly significant," says Nieder.

The researchers also realized that they could predict the upcoming number of crow calls based on the sound of the first call, suggesting that the birds planned the number of calls in advance. "This indicates that it's really a cognitive controlled process," he says.

As bright as they are, the crows did make mistakes. On the basis of the sound of the calls, the authors concluded that the birds generally set out to produce the correct number of caws, but sometimes lost track along the way. "When we analyse each individual call in such a sequence, we can predict whether the animal is stuttering — producing more vocalizations than we indicated — or whether the crow is skipping a specific vocalization, producing fewer than we had cued," Nieder says.

What the crows are doing is not what humans understand as "true" counting, which would require a symbolic understanding of numbers, notes Vallortigara. But it could be an evolutionary precursor of that ability. He adds that this type of research opens the door to understanding the neural mechanisms associated with these abilities and the unique aspects of how humans understand numbers. It even has implications for the study of cognitive disorders associated with numbers, such as dyscalculia.



  1. Liao, D. A., Brecht, K. F., Veit, L. & Nieder, A. Science (2024).

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