Crows and ravens (collectively known as corvids) attract people’s attention due to their intelligence: they perform various tricks, imitate speech, or hold “funerals.” Thanks to the results new research our understanding of their capabilities continues to expand: scientists from the University of Tübingen have discovered for the first time that ravens can operate with statistics. These results may help scientists better understand the evolution of intelligence (and perhaps help us better understand what’s going on in our heads).
Crows, whose number exceeds 27 million individuals, are almost universally distributed throughout North America and Eurasia. Their loud “caw” is hard to miss, and the tone of these calls changes depending on what the birds want to communicate. Like other birds of prey, crows have large brains for their size and a particularly pronounced forebrain, which in humans is associated with statistical and analytical thinking. Because of these qualities, ornithologists and animal behaviorists have discovered various “intelligent” behaviors in crows, such as using branches as tools to extract beetles from tree bark. Some experts have even classified crows as having intelligence equal to that of a 7-year-old child.
In addition to using tools, corvids are also capable of performing basic mathematical functions such as addition and subtraction. “In the natural world, very few animals have mathematical intelligence (beyond basic quantity discrimination)—things like numerical competence, arithmetic understanding, abstract reasoning, and symbolic representation,” explained Dr. Kaeli Swift, a postdoctoral researcher in avian behavior at the University of Washington (she is not took part in the Current Biology study). “The fact that several species of corncrakes have some of these skills makes them special.”
Dr. Melissa Johnston, a Humboldt Fellow at the University of Tübingen, appreciated the peculiarity of these creatures because she and her colleagues have been studying these animals for several years. “Our lab has shown that crows have complex numerical competence, abstract thinking, and careful decision making,” she says. In their latest experiment, Johnston and her team took these abilities to a new limit by testing statistical reasoning.
A Crow’s Guide to Statistical Thinking
Research involving crows is not for the faint of heart. “We can’t ask a crow a verbal question (as we typically do with humans) and expect an answer,” Johnston says. “So, as with teaching any complex task, we start with an easy option and gradually increase the complexity of the task as the subject’s skills develop.”
To do this, Johnston and her team began by training two crows to peck at various images on touch screens to obtain a treat. Starting with this simple “peck and get a treat” procedure, the researchers then upped the ante. “We introduced the concept of probability, for example that not every click on an image will result in a reward,” Johnston explained. “At this point, the crows learn to make unique pairs between the image on the screen and the likelihood of receiving a reward.” The crows quickly learned to associate each image with a different probability of receiving a reward.
In the experiment, two crows had to choose one of two images, each of which corresponded to a different probability of reward. “The crows were tasked with learning fairly abstract quantities (i.e., not whole numbers), associating them with abstract symbols, and then applying that combination of information to maximize rewards,” Johnston said. Over 10 days of training and 5,000 trials, the researchers found that both crows continued to choose the higher reward probability, indicating their statistical reasoning abilities.
Statistical reasoning involves using limited information about a situation to draw conclusions and make decisions. People use statistical inference every day without even realizing it, for example when deciding which café will have the most empty seats for a group of friends. “You only have time to visit one café, so you might think back to your previous visits and conclude that café A had tables available (relatively) more often than café B, and thus choose Cafe A.” – Johnston added. “You are not guaranteed a table in either case, but one of the options is rated as the best.” Similarly, the crows learned connections between touch screen images and reward probability and used that memory to get the biggest reward most of the time.
Johnston and her colleagues further encouraged the crows to wait a full month before retesting. Even after a month of no training, the crows remembered the reward probabilities and were able to choose the highest number every time. Johnston and her team were delighted that the crows could use statistical reasoning in almost any environment to obtain rewards. “Working with birds every day is extremely rewarding! They are very compassionate animals, so I enjoy spending time with them,” adds Johnston.
Animal intelligence from a bird’s eye view
Crows are one of the few animals that successfully adapt to urbanization, which is undoubtedly due to their intelligence. These birds often use man-made structures such as tunnels as a place to stay warm during the winter months. This is why urban ecologists classify birds as “exploiters” because they are not only tolerant of humans, but thrive in urban environments. Johnston and her colleagues found that some of this exploitation may be due to the birds’ ability to reason statistically. “Wild crows may use statistical inference in their ecologically motivated behavior; although I doubt they have crow cafes, they do have different locations they visit associated with different levels of foraging success,” Johnson adds.
As research reveals more about the intelligence of crows, public opinion about these birds continues to change. Historically, crows and ravens symbolize death. It doesn’t help that in English a group of crows is called a “murder” [murder of crows]and groups of ravens – “hanged” [hanger of ravens]. “In the West, crows are viewed with a mixture of adoration and hostility,” Swift says. “Many people crave interaction with crows, others consider them pests and look forward to dealing with them.”
Fortunately, these animals are protected under the Migratory Bird Treaty Act. However, this law does not prevent some states from selling crow hunting licenses during certain periods of the year. “There are still plenty of people who would happily get an annual crow hunting license and shoot a couple hundred for fun,” Swift said.
However, more and more people are beginning to appreciate the intelligence of these animals. From social media feeds dedicated to neighborhood crows to sports team mascots to important studies like this, more people are finding crows interesting and relatable. “I think for a lot of people, this research will make them appreciate crows in a way they didn’t appreciate them before,” Swift said. “They may start to actively pay attention to them because they learn about fun and interesting things they can do, like play. I think this research goes a long way toward improving our relationship with urban crows and changing the perception that they symbolize for us.”