Crows demonstrate keen counting skills through controlled vocalizations

Crows can control the number of vocalizations they produce, “counting” up to four in response to visual and auditory cues, researchers report. The findings suggest that the birds are capable of using a non-symbolic approximate number system, showing a level of vocal control that mirrors the early counting skills of human toddlers. 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. Here, Diana Liao and colleagues investigated whether carrion crows (Corvus corone) – one of the few bird species possessing both numerical competency and volitional vocal control – can control the number of vocalizations they produce to solve complex vocal response tasks. Liao et al. trained 3 crows to produce 1 to 4 vocalizations in response to both visual (colored numeral) and auditory (distinct sound) cues, which were associated with numerical values. In each trial, crows had to produce a target number of vocalizations and indicate the end of the vocal sequence by pecking at a target. The authors 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. According to the findings, 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. “This competency in crows also mirrors toddlers’ enumeration skills before they learn to understand cardinal number words and may therefore constitute an evolutionary precursor of true counting where numbers are part of a combinatorial symbol system,” Liao et al. write.