The brain of the common raven is among the largest of any bird species. Specifically, their hyperpallium is large for a bird. They display ability in problem-solving, as well as other cognitive processes such as imitation and insight.
Linguist Derek Bickerton, building on the work of biologist Bernd Heinrich, has argued that ravens are one of only four known animals (the others being bees, ants, and humans) who have demonstrated displacement, the capacity to communicate about objects or events that are distant in space or time. Subadult ravens roost together at night, but usually forage alone during the day. However, when one discovers a large carcass guarded by a pair of adult ravens, the unmated raven will return to the roost and communicate the find. The following day, a flock of unmated ravens will fly to the carcass and chase off the adults. Bickerton argues that the advent of linguistic displacement was perhaps the most important event in the evolution of human language, and that ravens are the only other vertebrate to share this with humans.
One experiment designed to evaluate insight and problem-solving ability involved a piece of meat attached to a string hanging from a perch. To reach the food, the bird needed to stand on the perch, pull the string up a little at a time, and step on the loops to gradually shorten the string. Four of five common ravens eventually succeeded, and “the transition from no success (ignoring the food or merely yanking at the string) to constant reliable access (pulling up the meat) occurred with no demonstrable trial-and-error learning.” This supports the hypothesis that common ravens are ‘inventors’, implying that they can solve problems. Many of the feats of common ravens were formerly argued to be stereotyped innate behavior, but it now has been established that their aptitudes for solving problems individually and learning from each other reflect a flexible capacity for intelligent insight unusual among non-human animals. Another experiment showed that some common ravens could intentionally deceive their conspecifics.
A study published in 2011 found that ravens can recognize when they are given an unfair trade during reciprocal interactions with conspecifics or humans, retaining memory of the interaction for a prolonged period of time. Birds that were given a fair trade by experimenters were found to prefer interacting with these experimenters compared to those that did not. Furthermore, ravens in the wild have also been observed to stop cooperating with other ravens if they observe them cheating during group tasks.
Common ravens have been observed calling wolves to the site of dead animals. The wolves open the carcass, leaving the scraps more accessible to the birds. They watch where other common ravens bury their food and remember the locations of each other’s food caches, so they can steal from them. This type of theft occurs so regularly that common ravens will fly extra distances from a food source to find better hiding places for food. They have also been observed pretending to make a cache without actually depositing the food, presumably to confuse onlookers.
Common ravens are known to steal and cache shiny objects such as pebbles, pieces of metal, and golf balls. One theory is that they hoard shiny objects to impress other ravens. Other research indicates that juveniles are deeply curious about all new things, and that common ravens retain an attraction to bright, round objects based on their similarity to bird eggs. Mature birds lose their intense interest in the unusual, and become highly neophobic.
The first large-scale assessment of ravens’ cognitive abilities suggests that, by four months of age, ravens do about as well as adult chimps and orangutans on tests of causal reasoning, social learning, theory of mind, etc.
