Scientists Suggest a New Layer to Crows’ Cognitive Complexity

The birds may be able to grasp a pattern-forming concept once thought to be unique to humans

A black crow sits on the branch of a walnut tree
Previous research has demonstrated that crows can make tools and recognize faces. Getty Images

Time and again, it seems, research has revealed crows performing some cognitive task that defies our expectations. Now, a new paper claims the birds can understand a certain kind of pattern, displaying an ability that scientists once thought was unique to humans.

Researchers tested whether crows can grasp the concept of recursion, which they define as “the process of embedding structures within similar structures” in their paper published in November in Science Advances.

Humans use recursion in language when we embed one clause within another to form a complex sentence, writes Scientific American’s Diana Kwon. For example, if a human says, “The ball the bat hit flew,” they’ve nested the clause “the bat hit” inside of “the ball flew.”

Scientists have long wondered whether understanding these patterns is unique to humans. “There’s always been interest in whether or not nonhuman animals can also grasp recursive sequences,” Diana Liao, the study's lead author who studies bird cognition at the University of Tübingen in Germany, tells Scientific American. In the early 2000s, linguists hypothesized that human language is the only form of animal communication that uses recursion, according to the Wall Street Journal’s Dominique Mosbergen.

However, in a 2020 study also published in Science Advances, researchers proposed that rhesus macaque monkeys might be able to create recursive sequences as well. The monkeys performed at the level of 3- to 5-year-old human children given the same sequence-creating task, but they required more training to do so, according to the Wall Street Journal.

In the new study, the researchers performed a similar experiment on two crows. They trained the birds to peck at sets of brackets, such as { } and [ ], in a recursive pattern, for example, { [ ] }. During training, the crows received birdseed pellets or mealworms for successfully forming recursive sequences, per the Wall Street Journal.

Then, when presented with pairs of brackets that they hadn’t seen before—such as ( [ ] )—the crows correctly formed embedded structures around 40 percent of the time. They had a similar success rate to children and performed better than the monkeys in the 2020 study, per the Wall Street Journal. They also didn’t need the extra training the monkeys received.

While the study only used two crows, that doesn’t necessarily mean the findings aren’t noteworthy. “It is a small sample size, which means you can’t make generalizations about populations of crows, but that wasn’t the point,” Stephen Ferrigno, a cognitive scientist at the University of Wisconsin-Madison who co-authored the 2020 monkey study but was not involved with the new paper, tells the Wall Street Journal. “All you need is a single example showing that crows can do this.”

Some other researchers aren’t persuaded by the study's conclusions. Noam Chomsky, one of the linguists who first suggested recursion is unique to human communication, tells the Wall Street Journal he isn’t convinced either study demonstrates that non-humans understand recursion.

After all, it’s possible that the birds learned to peck the shapes in the right order without actually grasping the bracket-nesting concept. Arnaud Rey, a psychologist at the French National Center for Scientific Research, tells Scientific American that the findings could be interpreted as the birds simply learning to link one bracket to the next, as opposed to embedding one pair inside another.

Either way, the paper is not the first to suggest that crows could be more cognitively complex than we might assume. Other research has found that crows can make tools and store them for future use. The birds can also recognize their own faces (and remember humans’ faces), writes Haaretz’s Ruth Schuster.

“To me, this [study] just adds to the catalog of amazing data showing that birds have been completely misunderstood,” Mathias Osvath, a cognitive scientist at Lund University in Sweden who did not contribute to the new research, tells Scientific American. “Saying that mammals took over the world cognitively is just simply wrong.”