Cognitive Discovery: Crows Demonstrate Capacity to Plan Number of Calls
In behavioral experiments, crows can learn to make a predetermined number of calls. They plan in advance: the sound of the first call in a counting sequence can be used to predict how many calls the crow will make. This was discovered by a research team consisting of Diana A. Liao, Dr. Katharina F. Brecht and junior professor Lena Veit under the direction of Professor Andreas Nieder from the Institute of Neurobiology at the University of Tübingen. Their study was published in the journal Science.
Carrion crows, which are songbirds, are not known for the beauty of their song, but for their outstanding ability to learn. Previous studies have shown that the birds have an understanding of numbers. “They also have very good control over their voices. They can precisely control whether they want to make a call or not,” reports Andreas Nieder. Together with his team, he conducted behavioral experiments with three carrion crows to investigate whether they can use these skills in combination.
Formation of an abstract concept
The birds were given the task of producing one to four calls after being presented with different picture symbols or when certain tones were heard, and of concluding their call sequence by pecking a confirmation button. “All three birds succeeded in doing this. They were able to count their calls in the sequence,” says Nieder. The reaction time between the presentation of the stimulus and the emission of the first call in response was relatively long, and the longer the more calls were required. The length of the delay was independent of the type of cue stimulus, image or sound. “This suggests that the crows form an abstract numerical concept from the information presented, which they use to plan their vocalizations before emitting the calls,” explains the researcher.
This finding is strengthened by the analysis of the individual crow calls in a sequence. “Based on the acoustic properties of the first call in a counting sequence, we were able to predict how many calls the crow would make,” reports Nieder. However, the crows do not manage this without errors. “Counting errors, such as one call too many or one too few, arise because the bird loses track of the calls already made or those still to be made during the sequence. We can also read the errors from the acoustic properties of the individual calls.”
The ability to intentionally produce a certain number of vocalizations requires a highly developed combination of numerical competence and vocal control. “Our results show that this is not reserved for humans alone. In principle, it also opens up sophisticated communication to corvids,” says Nieder.