We often use the phrase ‘birdbrain’ as a mild insult, to mean someone who is dim-witted or acts stupidly. Birds’ brains are indeed much smaller, and far less convoluted, than our own, but our feathered friends have had a bad press, and some of them – the corvids, in particular – are capable of remarkable feats of intelligence.

Crows, for example, can apparently contemplate death, and have tool-making abilities that are at least as sophisticated as, or may even surpass, those of monkeys. And Clarke’s nutcrackers can harvest tens of thousands of pine seeds, and cache them in thousands of different locations. If they notice another nutcracker watching them burying their food supply, they return later on to hide that cache elsewhere. When winter sets in, they can retrieve the seeds from all the locations, relying solely on spatial memory.

A new study by researchers at the University of Vienna now expands the corvids’ repertoire of cognitive capabilities even further. It shows that ravens can not only coordinate their actions and cooperate to solve problems, but can also remember other birds that cheated on them in the task, and refuse to work with them again.

Cooperation is an important aspect of social life, and is widespread throughout the animal kingdom. Lions, chimps, and killer whales all cooperate when hunting prey, and even fish of different species can work together and use their complementary skills in joint hunts. Brown-necked ravens have been seen cooperating to trap and kill lizards in the wild, but so far this type behaviour has not been studied experimentally in any detail.



Jorg Massen and his colleagues tested the cooperative problem-solving abilities of common ravens in a series of ‘loose-string’ experiments. In this set-up, pairs of birds have to pull the two ends of a piece of string simultaneously, in order to bring a small feeding platform within reach. If one of the birds pulls alone, they unthread the string and the platform remains where it is, so that neither of them can get the food.

In the first experiment, each of seven juvenile common ravens performed the loose-string test 20 times in 30 different sessions. The ravens cooperated successfully on 397 of these 600 tests, with each individual bird succeeding in getting food at least 32 times. The researchers noticed that there was a great deal of variation, however, with 3 of the 21 possible pairs of birds never managing to successfully cooperate with each other.

To understand why, they repeated the experiment with the same seven ravens and two additional birds, testing each individual twice with all the others, and taking into account factors such as sex, kinship, and the birds’ position in the group hierarchy. This revealed that the birds cooperated better with partners of the opposite sex, and were more likely to do so with relatives than with with strangers. And the more closely ranked were any two individuals within the group dominance hierarchy, the less likely they were to cooperate with each other.

The birds paid little or no attention to their partner’s actions, but reacted to how the food rewards were distributed at the end of each trial. In both experiments, the higher-ranking individual sometimes took both pieces of food for themselves, and in these cases, the bird that did not receive a food reward was far less likely to cooperate with the cheater the next time around, and also with others. Conversely, successful cooperation the made both individuals in the pair more likely to work together the second time round.

This shows that ravens can spontaneously cooperate to solve the loose-string problem, and that they do not cooperate indiscriminately, but prefer to do so with some individuals over others. Previous work has shown that kinship enhances the likelihood of successful cooperation in birds, chimps, and other social animals, but this is the first study to show that birds’ behaviour is influenced by their partners’ earlier behaviour, according to some sort of tit-for-tat rule.

Ravens have a natural propensity to cooperate with each other, and so they could serve as an interesting model for studying the evolution of cooperation, and the factors that influence how, why, and when we choose to cooperate. The study demonstrates that ravens have cognitive abilities once thought to be unique to humans and chimps, but it also reveals something about the dark side of their nature and, perhaps, that of humans - birds that got away with cheating once were more likely to cheat again later, and did so whenever the opportunity arose.

Reference



Massen, J. J. M., et al. (2015). Tolerance and reward equity predict cooperation in ravens (Corvus corax). Sci. Reports 5: 15021. DOI: 10.1038/srep15021 [Full text]