For the first time, research reveals crows use statistical logic

Whether playing tricks, mimicking speech, or holding “funerals,” crows and ravens (collectively known as corvids) have captured the public’s attention due to their unexpected intelligence. Thanks to results from a new Current Biology study, our understanding of their capabilities only continues to grow, as researchers from the University of Tübingen found for the first time that crows can perform statistical reasoning. These results can help scientists better understand the evolution of intelligence (and may give us a better appreciation of what’s going on in our backyard).

Bird brains

With a population of over 27 million and counting, crows seem almost ubiquitous across the US. Their loud “caws” are hard to miss, and the tone of these cries varies depending on what the birds are communicating. Like other corvids, crows have a large brain for their size and a particularly pronounced forebrain, which is associated with statistical and analytical reasoning in humans. Thanks to these attributes, ornithologists and animal behaviorists have found crows doing various “intelligent” activities, such as using twigs as tools to extract bugs from tree bark. Some experts have even classified corvids as having the same intelligence as a 7-year-old child.

Beyond using tools, corvids can also do basic mathematical functions, like adding or subtracting. “In the scheme of the natural world, very few animals are demonstrated to possess much in the way of mathematical intelligence (beyond basic numerical discrimination)—things like numerical competence, an understanding of arithmetic, abstract thinking, and symbolic representation,” explained Dr. Kaeli Swift, a postdoctoral researcher in bird behavior at the University of Washington (she was not involved in the Current Biology study). “That several corvid species have been demonstrated to possess some of these skills makes them quite special.”

Dr. Melissa Johnston, a Humboldt Fellow at the University of Tübingen, certainly appreciated the specialness of these creatures, as she and her colleagues have been studying these animals for several years. “In our lab, it has been shown that crows have sophisticated numerical competence, demonstrate abstract thinking, and show careful consideration during decision-making,” she said. In her most recent experiment, Johnston and her team pushed these abilities to a new extreme, testing statistical reasoning.

A crows’ guide to statistical reasoning

Studies involving crows are not for the faint-hearted. “A lot of training goes into experiments such as this, as we cannot ask a crow a verbal question (the way we generally do with humans) and expect an answer,” Johnston said. “Therefore, as one would do when teaching any complex task, we start with a simple version and increase the complexity step-by-step as the subject develops their skills.”

To do this, Johnston and her team began by training two crows to peck at various images on touchscreens to earn food treats. From this simple routine of peck-then-treat, the researchers significantly raised the stakes. “We introduce the concept of probabilities, such as that not every peck to an image will result in a reward,” Johnston elaborated. “This is where the crows learn the unique pairings between the image on the screen and the likelihood of obtaining a reward.” The crows quickly learned to associate each of the images with a different reward probability.

In the experiment, the two crows had to choose between two of these images, each corresponding to a different reward probability. “Crows were tasked with learning rather abstract quantities (i.e., not whole numbers), associating them with abstract symbols, and then applying that combination of information in a reward maximizing way,” Johnston said. Over 10 days of training and 5,000 trials, the researchers found that the two crows continued to pick the higher probability of reward, showing their ability to use statistical inference.

Statistical inference involves using limited information about a situation to draw conclusions and make decisions. People use statistical inference daily without even realizing it, such as when deciding which café will have more seating available for a group of friends. “You only have time to visit one, so you might think back to your previous visits and conclude that there were tables available (relatively) more often at Café A compared to Café B and thus opt to visit Café A,” added Johnston. “You’re not guaranteed a table in either case, but one is judged as the better option.” Similarly, the crows remembered the connections between the images on the touchscreen and the reward probabilities and used that memory to ensure they would get the highest reward in most cases.

Pushing the crows even further, Johnston and her team waited a whole month before testing the crows again. Even after a month without training, the crows remembered the reward probabilities and could pick the highest number every time. Johnston and her team were excited that the crows could apply statistical reasoning in almost any setting to ensure their reward. "Working with the birds every day is very rewarding! They are very responsive animals, so I enjoy spending time with them,” added Johnston.

A bird’s-eye view of animal intelligence

Crows are among the few animals to adapt to urbanization successfully, undoubtedly due to their intelligence. These birds often utilize artificial structures, such as tunnels, as places to keep warm during the winter months. These behaviors are why urban ecologists classify corvids as "exploiters," as they don’t just tolerate humans but actually thrive in urban environments. As Johnston and her team found, part of this exploitation could be due to the birds' abilities to use statistical reasoning. “Wild crows may use statistical inference in their ecologically motivated behavior; while I doubt they have crow cafés, they will have various locations they visit associated with differing levels of foraging success,” added Johnson.

As studies further reveal the intelligence of corvids, the public perception of these birds continues to change. Historically, crows and ravens symbolized death. It doesn’t help that groupings of crows are called "murders," while groups of ravens are termed "hangings" by scientists. "In the West, crows are viewed with a mixture of adoration and animosity,” said Swift. “While many people covet relationships with crows, others view them as pests and look forward to opportunities to control them."

Thankfully, these animals are protected by the Migratory Bird Treaty Act. That law doesn’t stop some states from selling crow hunting licenses during parts of the year, though. “There are still plenty of people who will gleefully get their annual crow license and shoot a couple hundred for fun,” Swift noted.

However, more of the public is beginning to appreciate the intelligence of these animals. From social media channels for neighborhood crows to sports team mascots and essential studies like this one, more people view crows as engaging and relatable. “I think for a lot of people, these studies make them appreciate crows in ways they didn't before,” Swift said. “They may start to actively pay more attention to them because they become aware of fun and exciting things they might see them do, like play. I think these studies do a lot to help improve our relationship with urban crows and change the tide on what they symbolize to us.”

Current Biology, 2023. DOI: 10.1016/j.cub.2023.06.023