Crows are highly intelligent, social birds found on every continent other than South America and Antarctica.

In a new study, researchers from the Institute of Neurobiology at Germany’s University of Tübingen have found that crows are able to learn to produce a specific number of calls, showing advance planning.

How many calls they will make can be predicted from the first vocalization in a sequence, a press release from University of Tübingen said.

“Producing a specific number of vocalizations with purpose requires a sophisticated combination of numerical abilities and vocal control,” the researchers wrote in the study. “We show that crows can flexibly produce variable numbers of one to four vocalizations in response to arbitrary cues associated with numerical values. The acoustic features of the first vocalization of a sequence were predictive of the total number of vocalizations, indicating a planning process. Moreover, the acoustic features of vocal units predicted their order in the sequence and could be used to read out counting errors during vocal production.”

Carrion crows are known for their impressive learning ability, which includes being able to count.

“In addition, they have very good vocal control. They can control precisely whether they want to emit a call or not,” said Andreas Nieder, a professor of animal physiology at University of Tübingen, in the press release.

The research team conducted behavioral experiments to see if three carrion crows could combine their ability to count with vocal control.

The corvids were given the task of producing from one to four calls that appropriately corresponded with specific sounds or an array of Arabic numerals, followed by pecking an enter key.

“All three birds succeeded in this. They were able to count their calls in sequence,” Nieder said in the press release.

The crows displayed a relatively long response time between when they were presented with the stimulus and their first call, which became longer as more calls were added. The delay’s length was not affected by the type of stimulus.

“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,” Nieder explained. “Using the acoustic properties of the first call in a numerical sequence we could predict how many calls the crow would make.”

Some errors were detected in the birds’ calls.

“Counting errors, such as one call too many or one too few, arose through the bird losing track of the calls already made or still to be produced,” Nieder said. “We are also able to read out these types of errors from the acoustic properties of the individual calls.”

Being able to produce a deliberately chosen number of calls requires a sophisticated combination of vocal control and numerical competence.

“Our results show that humans are not the only ones who can do this. In principle it also opens up sophisticated communication to the crows,” Nieder said.

The study, “Crows ‘count’ the number of self-generated vocalizations,” was published in the journal Science.

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