Crows can count out loud, startling study reveals

Crows can count out loud, a startling new study has revealed, and they may even have the same numeracy skills as human toddlers.

Researchers found that carrion crows (Corvus corone) can produce a specific number of caws in response to visual or auditory stimuli, enabling them to count out loud between one and four. 

The discovery is the first time that animals have been definitively shown to count by making a distinct number of vocalizations. The researchers published their findings Thursday (May 23) in the journal Science.

"Producing a specific number of vocalizations with purpose requires a sophisticated combination of numerical abilities and vocal control," the researchers wrote in the study. "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." 

Many studies have shown that animals, including honeybees, lions, frogs and ants, have an inherent numerical sense, and another study revealed that black-capped chickadees (Poecile atricapillus) add more "dee'"trills at the end of their alarm calls to alert to more significant threats. Yet none of these provide enough evidence that animals share humans' ability to count out loud — for instance, in the example of the chickadees, the birds may only be calling more frequently as a result of heightened stress.

Related: Crows outthink monkeys, can grasp recursive patterns

To look for stronger evidence of vocal animal counting, the researchers turned to carrion crows, a promising candidate for the test due to their superb vocal abilities and comprehension of complex mathematical concepts such as zero.