Crows ‘count’ the number of self-generated vocalizations

Producing a specific number of vocalizations with purpose requires a sophisticated combination of numerical abilities and vocal control. Whether any animal possesses such a capacity to voluntarily control the number of self-generated vocalizations is yet unknown. We demonstrate that crows can flexibly produce a variable number 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 were foretelling of their order in the sequence and could be used to read-out counting errors during vocal production. Together, the crows' vocal enumeration capability could be an evolutionary precursor to symbolic counting found uniquely in humans.