Crows Can Count Aloud, Scientists Discover

Corvids are widely recognised for remarkable displays of inventive and intelligent thought, but a newly identified skill has left researchers astonished.

A group of scientists has demonstrated that crows can ‘count’ aloud, giving a precise, intentional number of caws after visual or sound-based prompts. Although animals including honeybees have been found able to grasp numbers, this particular expression of numerical literacy has not previously been recorded in another non-human species.

Crows can count aloud using vocal cues

"Producing a specific number of vocalizations with purpose requires a sophisticated combination of numerical abilities and vocal control," writes the team of researchers led by neuroscientist Diana Liao of the University of Tübingen in Germany.

"Whether this capacity exists in animals other than humans is yet unknown. We show that crows can flexibly produce variable numbers of one to four vocalizations in response to arbitrary cues associated with numerical values."

Counting aloud differs from merely understanding numbers. As well as numerical comprehension, it demands deliberate control of vocalisations for communicative purposes. Humans are known to use speech both to count and to convey quantities, a skill introduced early in life.

While toddlers are learning to count, it may take them some time to master the particular number words linked with particular quantities. During this stage, children may create a spoken tally with random number words. Rather than saying “one, two, three”, they could say “one, one, four” or “three, ten, one”. Their number of vocalisations is right, even though the words are mixed up.

Testing carrion crows’ numerical skills

The biological roots of symbolic counting remain uncertain. However, because crows are already known to understand challenging numerical ideas, including zero, Liao and her colleagues considered them strong candidates for studying more advanced number abilities.

The scientists examined three carrion crows (Corvus corone). They trained the birds to make a varying number of vocalisations, from one to four, when presented with an arbitrary symbol or audio signal. After producing the required number of caws, each crow had to peck a target to indicate it had finished.

The researchers found that all three crows could give the correct number of caws in response to the prompts. Their occasional mistakes generally involved making one caw too many or one too few.

According to the team, this resembles the way human toddlers count: through a non-symbolic approximate number system, planned before the initial vocalisation.

Notably, both the timing and sound of the first call in a sequence were associated with the number of calls that followed. Each call within a sequence also displayed acoustic characteristics tied to its position in that sequence.

The accomplishment is particularly striking in crows because intentional vocalisations are harder to produce, and involve longer response times, than actions such as pecking or moving the head.

What crows’ counting could mean for communication

It may point to a previously unrecognised route for bird communication in the wild. Chickadees, for example, add more “dee” sounds to their alarm calls when faced with larger predators.

"Our results demonstrate that crows can flexibly and deliberately produce an instructed number of vocalizations by using the 'approximate number system', a non-symbolic number estimation system shared by humans and animals," the researchers write in their paper.

"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."

The research was published in Science.