Carrion crows (Corvus corone) can control the number of vocalizations they produce, counting up to four in response to visual and auditory cues, according to a study published in the journal Science.
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The carrion crow (Corvus corone). Image credit: Andreas Nieder.
Counting out loud — reciting one, two, three, and so on, for example — requires understanding numerical quantities and purposeful vocal control.
Humans use speech to symbolically count and communicate quantities, a complex skill developed in childhood.
Before mastering symbolic counting, where specific words relate to specific quantities, toddlers will often produce a number of speech sounds that match the quantity of objects they see, using these sounds as acoustic tallies to convey the corresponding number.
This early behavior in humans reflects non-symbolic competencies shared with animals.
Several animals have shown their ability to discriminate between different numbers of objects and to convey information through differing numbers of vocalizations.
However, whether non-human animals have the ability to count by deliberately producing specific numbers of vocalizations remains unknown.
“Carrion crows, which belong to the group of songbirds, are not known for the beauty of their song but for their formidable learning ability,” said Professor Andreas Nieder, a researcher at the University of Tübingen.
“For instance, earlier studies have shown that the birds understand counting.”
“In addition, they have very good vocal control. They can control precisely whether they want to emit a call or not.”
In the study, Professor Nieder and co-authors investigated whether carrion crows can control the number of vocalizations they produce to solve complex vocal response tasks.
They trained three crows to produce one to four vocalizations in response to both visual (colored numeral) and auditory (distinct sound) cues, which were associated with numerical values.
In each trial, the birds had to produce a target number of vocalizations and indicate the end of the vocal sequence by pecking at a target.
The researchers found that the crows could produce specific numbers of vocalizations successfully and deliberately in response to specific cues — a degree of control not yet observed in other animals.
The birds used a non-symbolic approximate number system, planning the number of vocalizations before starting.
Further analysis showed that the initial vocalization’s timing and features predicted the number of subsequent vocalizations, and different acoustic features in vocalizations indicated the number within a given sequence.
“Our results show that humans are not the only ones who can do this,” Professor Nieder said.
“In principle, it also opens up sophisticated communication to the crows.”
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Diana A. Liao et al. 2024. Crows ‘count’ the number of self-generated vocalizations. Science 384 (6698): 874-877; doi: 10.1126/science.adl0984
