Crows Can Count Aloud Much Like Toddlers, New Study Finds

The cleverness of corvids has wowed scientists and casual birders for decades. Crows can use and even make tools, reason via analogies, and have been said to rival monkeys in cognitive capacity. They also seem to have a remarkable ability to understand numeric values. For instance, they recognize when different images show the same number of dots—even when the dots are of different sizes and in different arrangements.

Now a study published in the journal Science establishes that crows have counting abilities more sophisticated than anyone had realized—with the birds exhibiting behaviors very similar to toddlers first learning to count. The researchers found that crows can use their voices to communicate specific quantities, something they believe has never been documented before in animals other than humans. 

In the study, trained crows used a tallying approach to counting that mirrors the way young children first begin to communicate numbers. For example, if there are three apples on a tree, a toddler may say “‘one, two, three,” or “one, one, one,” —with the number of sounds matching the number of objects, even when the words do not. “Crows are doing something similar,” says Diana Liao, the study’s lead author. These abilities, she notes, may be an evolutionary precursor to symbolic counting, which only humans do.

Other bird species have been observed to use chirps in ways that seemingly convey magnitude, but not in such a precise way. Chickadees do this by chirping extra syllables in a sequence to indicate an extra-large wingspan of a nearby raptor, according to a 2005 study—though in that work, it wasn’t clear if the birds intentionally scale up their calls, or if this is an involuntary fearful or alarmed reaction, like a surprised person yelping.

Inspired in part by this research, Liao, a neurobiologist at the University of Tübingen in Germany, wanted to know if crows could go a step beyond and actively control their caws to express a specific numeric value, rather than just a general observation that something is bigger or smaller.

To test that, Liao and her coauthors trained three Carrion Crows over more than a year. The scientists displayed the numbers 1 to 4 on a screen and played between 1 and 4 tones on a speaker. Enticed with mealworms and pellets, the crows learned to produce a sequence of caws that corresponded to each cue’s number and peck a circle on a touchscreen when finished—the functional equivalent of an “enter key.”

The crows generally did well on these assignments, though as the numbers got larger, they paused for longer before answering and were more likely to make errors. Overall, Liao says it was exciting to see the crows get their heads around the concept. “This is a difficult task to control the number of vocalizations, and it was very impressive to see when they made the connection between these cues and the response and then continued to make the correct responses,” she says. 

To better understand these results, Liao and her colleagues also used recordings of the crows’ responses to train an algorithm to correctly predict the answer to each exercise based only on the crows’ very first caw alone. The fact that this worked is evidence that the crows planned out their responses before vocalizing them, she says.

John Marzluff, a University of Washington professor emeritus of wildlife science who wasn’t involved in the research, says he was most impressed with the fact that the crows took longer to begin more complex sequences. This, he says, reflects the process of making mental plans, and it mirrors the way humans, when queried, may pause to collect their thoughts before delivering complex statements.  “It seems crows do the same, which is very intriguing,” he says.

How and whether this out-loud counting ability might help crows in the wild is a remaining key question. In general, there are clear survival benefits for birds to understanding quantities, such as recognizing the exact number of nearby predators or potential mates. Marzluff notes counting skills can help birds keep track of how many eggs are in a nest “to make sure they haven’t been cuckolded” by another avian species. Counting abilities, he adds, might also empower crows to calculate whether the payoff from a foraging endeavor was worth the effort.    

For communicating specific numeric values to be actually helpful in the wild, other crows—and maybe even other eavesdropping birds—would also have to understand the message. That crows have developed the skills to vocalize this type of information suggests to Marzluff that it could have social value, like in coordinating actions between avian pairs or groups.

The research did not look at any of these possibilities, but Liao says future work, still in preliminary planning stages, might. “I would love to follow up on this particular part,” she says. “Like, what is the ecological relevance of this ability to control the number of vocalizations?”  

That crows have developed cognitive abilities so similar to humans’—even though their respective lineages diverged 300 million years ago—is remarkable to Liao. “It’s interesting to think about how very different brains support similar behaviors,” she says.