It’s no secret that corvids are capable of some amazing displays of creative and intelligent thinking, but one newfound ability has us amazed.
A team of scientists has shown that ravens can ‘count’ out loud – producing a specific and deliberate number of caws in response to visual and auditory cues. While other animals such as honey bees have shown the ability to understand numbers, this specific display of numerical literacy has not yet been observed in any other non-human species.
“Producing a certain number of vocalizations with a purpose requires a sophisticated combination of numerical abilities and vocal control,” wrote the team of researchers led by neuroscientist Diana Liao of the University of Tübingen in Germany.
“It is not yet known whether this capacity exists in animals other than humans.” We show that ravens can flexibly produce variable numbers of one to four vocalizations in response to arbitrary cues associated with numerical values.”
The ability to count aloud is different from understanding numbers. It requires not only this understanding, but also purposeful voice control for the purpose of communication. Humans are known to use speech to count numbers and communicate quantities, an ability learned by young people.
When young children are learning to count, learning the specific numbers associated with specific quantities can take some time to master. Meanwhile, children can sometimes use random numbers to make a voice score. Instead of counting “one, two, three,” they can say “one, one, four” or “three, ten, one.” The number of vocalizations is correct, but the words themselves are messed up.
The biological origins of symbolic counting are unknown, but since ravens are known to understand difficult numerical concepts such as zero, Liao and colleagues believe they represent a good candidate for studying more complex counting skills.
They conducted their study on three scrawny crows (Corvus corone), which the researchers trained to produce a variable number of vocalizations, between one and four, after being shown a random symbol or sound cue. After producing the required number of crows, the ravens had to peck at a target to indicate they were ready.
The researchers found that all three ravens were able to produce the correct number of caws in response to the cues, with the random error mostly appearing as one caw too many or too few.
The researchers say this is similar to how human toddlers count using a non-symbolic approximate number system that is planned in advance before the first vocalization.
Interestingly, the timing and pitch of the first vocalization in a sequence was related to how many vocalizations were made subsequently, and each vocalization in a sequence had acoustic characteristics specific to its place in that sequence.
The achievement is particularly impressive for ravens, as deliberate vocalizations are more difficult to produce and have a longer reaction time than, say, pecking or head movements.
It may indicate a previously unknown channel of avian communication in the wild. Chickadees, for example, make more “dee” sounds in their alarm signals for larger predators.
“Our results show that ravens can flexibly and consciously produce an instructed number of vocalizations using the ‘approximate number system,’ a non-symbolic number estimation system shared by humans and animals,” the researchers wrote in their paper.
“This competence in ravens also reflects young children’s enumeration skills before they learn to understand the main number words and may therefore represent an evolutionary precursor to true counting, where numbers are part of a combinatorial symbol system.”
The study was published in Science.
