One of the most common audience queries that follow my public corvids presentation is, “Who’s smarter, a raven or a ___ ?” The blank can been filled in by any number of animals, but most people want to know either how various corvids scale against each other, or how corvids like ravens compare against other animals known for their intelligence, such as primates, dolphins, or elephants. Inevitably, people are somewhat disappointed by my answer. As I’ve written about previously, trying to rank animals in this way is a precarious exercise. As an animal behaviorist, I of course think exploring the cognitive abilities of animals is fascinating and worth doing, but ranking them in the absence of any kind of consideration of why different animals display some cognitive skills and not others makes intelligence seem like some kind of evolutionary race. Instead, like all things, the possession of higher order cognition is simply a byproduct of what happened to work in the reproductive favor of a particular species, and should not be interpreted as a reflection of value. Even if we weren’t concerned about the ethical implications of these comparisons, the second issue with them is that they’re not very meaningful because different species have been presented with different tests which makes cross-species comparisons a bit apple and orange-y.
But while we should guard ourselves against the temptation to make intelligence a linear scale by which all life can be measured, we can acknowledge that a study by Pike et al. 2020 has made some incredible progression in solving that second issue.1 With their new testing paradigm, suddenly our apples and oranges are not so hard to compare after all. So let’s explore what’s interesting about the cognitive abilities of ravens and what exactly this study has shown us about what they have in common with some of our closest primate relatives.
Before diving into the details, we should take a moment to understand how animal behaviorists define intelligence* and how we are attempting to understand why corvids, primates, parrots, etc. have a mastery of higher-order cognitive skills that other animals do not appear to possess. In my field, the definition of intelligence is often described as the ability to flexibly solve problems using cognition rather than instinct or trial and error learning. Within that definition, “flexibility” and “cognition” are the keys because they strain out the behaviors that require things like insight, foresight, empathy, causal reasoning, etc. from those that are guided by simple, immovable mechanisms that can be carried out with little thought. Consider, for example, a bridge. Both humans and ants can build them; but whereas ants build them only in specific contexts and by the collective power of hundreds or thousands of individuals executing a simple task, humans can build them in a great many contexts because we understand and can manipulate complex properties of the physical world. The fact that both animals can accomplish bridge-building with such vast difference in our cognition warrants an interesting question: “Why did advanced cognitive abilities evolve in the first place?”
Although many explanation exist, the two I want to spend time on are the social intelligence hypothesis and the ecological intelligence hypothesis. The ecological intelligence hypothesis asserts that it is the harshness or complexity of the environment that drives advancing cognition (ex: the availability of novel foods that requires some problem solving to eat), while the social intelligence hypothesis suggests that it’s the demands of long lasting and complex social lives that most contributes to the intelligence of some species. While both ideas have supporting evidence, of most interest to the proponents of the social intelligence hypothesis is that social complexity (ex: the maintenance of long-term bonds that may include absences) is shown to correlate with relative brain size (specifically the neocortex) in mammals and birds. Of course, size isn’t everything, but those species still share other non-sized based brain features such as high neuronal connectivity, density and modularity. That birds such as corvids and parrots share these features with some mammals is especially striking given that birds and mammals diverged some 300 million years ago, and the resulting evolutionary differences in our brain architecture are evident.
When it comes to actually testing cognition, there are two main umbrellas of inquiry: social cognition and physical cognition. Social cognition refers to things like the ability to follow another individual’s gaze, learn a task from someone else, and interpret intentions. Physical cognition refers to things like object permanence (that objects continue to exist even though they can’t be seen), relative numbers, properties of tools, etc. Among corvids, New Caledonian crows have demonstrated remarkable physical cognition (they can infer an object’s weight by how it behaves in the wind!2), but because they’re not especially social corvids3, they have not demonstrated remarkable social cognition. Common ravens on the other hand, have social cognitive and potentially even physical skills that we believe rival that of primates. But because we’ve only tested corvids using a single cognitive paradigm at a time, we’ve been limited in our comparisons. Which is what makes the study by Pike et al. so unique. Theirs is the first to retool the Primate Cognitive Test Battery (which is the collective name for a suite of different cognitive tests that are routinely given to test primate intelligence) to assess the abilities of common ravens among nine physical and six social skills.
The nine physical skills were designed to test the eight study subjects’ understanding across three main themes: space, quantities and causality. Among the space tests the researchers were interested in evaluating how well ravens can understand object permanence and follow a moving object that is concealed (picture the classic shell game, but without the grift). For the quantities tests, the researchers presented ravens with things like a large and small pile of food to see which they would choose. Finally, for causality tests, they did things like let the ravens see them place a peanut in a cup, and then shake that cup vs. an empty one before allowing the bird to make a selection of which cup they wanted. Among the social skills, the researchers tested social learning, communication and theory of mind (the ability to think about the mental states of yourself and others). Each of these 6 total tests evaluated things like the being able to follow gaze, learn by instruction, and interpret intentions. Of course, all these tests were far more detailed and controlled than I am presenting them here; if you’d like a more detailed breakdown, you can read my personal, unedited, notes on the paper here.
Given their complex social lives and the abundance of data on raven social intelligence, the researchers expected to find that their subjects would perform better among the social tests relative to the physical ones, but that’s not what they found. To their surprise, the ravens actually performed similarly in both cognitive realms. This suggests that ravens possess a general intelligence and that the two realms may be linked enough in the brain that you can’t really disassociate one from the other. Still, across the 15 specific tests, ravens did better at some than others. For example, given their lifestyle as scavengers, it’s perhaps not surprising that among physical tests they performed the best at qualitative skills like assessing what pile of food was the biggest. Impressively, ravens were able to match adult-level success at many of these executive-order tasks starting at only 4 months old, which is younger than we typically see in parrots and even many primates. As for direct comparisons to primates, while ravens did significantly worse at spatial tests, they performed similarly to primates in quantitative and theory of mind tests, and only slightly worse in causal reasoning and communication. All in all, it seems ravens pretty closely match the performance of great apes across both social and physical cognition tests.
That said, there are some caveats to consider. First, these tests were administered by people, so there’s just no getting around the possibility of unintended influence. For example, previous studies have shown that ravens begin following the gaze of their flock mates around eight weeks old, by only start to follow the human gaze after fifteen weeks. So it’s possible that the birds’ responses to people among some of the social tests were more muted because they weren’t actually interacting with a fellow bird. Alternatively, they may have performed more poorly at some tasks because they viewed the experimenter as a competitor rather than as a neutral observer. There was also quite a bit of individual variation, and only a small number of birds were tested, so the researchers hesitate to make sweeping claims that the performance of these eight birds are representative. And when it comes to comparing ravens and primates, we’re back to our bridge dilemma because of course behavioral ability does not imply that the same complex cognitive mechanisms are at work.
Still, while these considerations are important, there’s no getting around that these birds demonstrated an incredible performance in both social and physical cognition tests. Put another way, an animal that diverged from mammals 300 million years ago, whose cortical architecture is significantly different, can play the shell game and scheme on their rivals just about as well as our closest relatives. So while I’ll continue to exercise restraint in answering, “Are ravens smarter than a ____ ?,” I have no doubt that these animals are as complex and enchanting as so many of us suspect them to be.
*To understand the topic at hand a discussion of cognitive intelligence and its definition is necessary, but it’s also worth learning about and unpacking why our judgement and language around intelligence as applied to people is increasingly considered harmful. Here are some resources to do that:
- S Pike, MJ Sima, CR Blum, E Herrmann and R Mundry. 2020. Ravens parallel great apes in in physical and social cognitive skills. Scientific Reports 10, 20617
- SA Jelbert, R Miller, M Schiestl, M Boeckle, LG Cheke, RD Gray, AH Taylor and NS Clayton. 2019. New Caledonian crows infer the weight of objects from observing their movements in a breeze. Proc. R. Soc. B 286: 20182332
- Holzhaider JC., Sibley MD, Taylor AH, Singh PJ, Gray RD, and Hunt GR. 2011. The social structure of New Caledonian crows. Animal Behaviour 81: 83-9