...complex cognition depends on a "tool kit" consisting of causal reasoning, flexibility, imagination, and prospection. Because corvids and apes share these cognitive tools, we argue that complex cognitive abilities evolved multiple times in distantly related species with vastly different brain structures in order to solve similar socioecological problems.The socioecological problems corvids and great apes have evolved to solve, say Emery and Clayton, include finding and keeping perishable foods over time and space, and understanding individual relationships in social groups. Emery and Clayton propose that corvids are more intelligent than any other bird, except perhaps parrots, and their intelligence rivals that of most non-human primates. Indeed, Clayton calls corvids "feathered apes". "You only have to look in the beady eye and see them watching you," she says.
Clayton told the radio presenter that she had her original inspiration jointly with Nathan Emery, now her husband, who was studying primates when they met as students. He was working on eye gaze, on which there's been a lot of work in primates, and they wondered whether they could collaborate on a project having to do with that. But, instead, Clayton was inspired by her daily walks around campus when she'd watch the local scrub jays stealing food from students eating lunch on the lawn.
Not only would these birds hide what they'd stolen for later, but Clayton observed that when they knew they'd been watched as they hid their find, they would re-hide it when no other birds were watching. This led Clayton and Emery to conceive of the corvid "theory of mind". Previously, it had been thought that only great apes and humans could imagine the future, and put themselves in it, but to Clayton the fact that these jays were sensitive to others watching, and changed their behavior based on that knowledge, meant that they are able to make interesting inferences and deductions that most other animals cannot. Dogs bury bones "but nobody has shown they are capable of putting themselves into another's shoes."
The crow has a brain significantly larger than would be predicted for its body size, and it is relatively the same size as the chimpanzee brain. The relative size of the forebrain in corvids is significantly larger than in other birds (with the exception of some parrots), particularly those areas thought to be analogous to the mammalian prefrontal cortex: the nidopallium and mesopallium. This enlargement of the “avian prefrontal cortex” may reflect an increase in primate-like intelligence in corvids.
|Illustration of the four nonverbal cognitive tools displayed by corvids and apes, which are proposed as the basis for complex cognition: causal reasoning (New Caledonian crow and chimpanzee tool use), imagination (insight in ravens and role taking in chimpanzees), flexibility (western scrub jays' flexible memory for degraded and fresh food items and tactical deception in apes), and prospection (western scrub jays recaching food and chimpanzees carrying stone tools). These cognitive tools interact in different ways to produce complex cognition. [Drawing by C. Cain]. From Science.|
These birds "travel mentally in time and space", that is, they plan for the future, including for tomorrow's breakfast, as described here. They can remember where they've hidden food; Clark's nutcrackers cache up to 30,000 pine seeds which they can retrieve up to 6 months later. Some corvids cache perishable foods, but don't eat them past their sell-by dates. These birds can watch others caching foods and pilfer them later, when the storer's not watching. Or they'll hide their stores behind barriers so that observers can't see its exact location, as in the video.
These birds may well be able to solve these 'socioecological' problems, but we do have to be careful about defining 'intelligence' in human terms, which is at least a bit circular. After all, other birds, closely related, relatively speaking, do perfectly well at what they do, and that involves using the brain to solve problems, assess their situation, and so on. This doesn't take away from corvid achievements, of course, but helps put things in perspective. If corvids actually have markedly better abilities at some kinds of problems solving that we seem to relate to our own, and are closely related to species that don't, then it could suggest that something relatively simple can lead to major jumps in such abilities.
Still, it's always interesting when human, or primate exceptionalism is challenged.