Ravens know the difference between fair and unfair, according to a new study, and avoid those who act unfairly towards them. Researchers found that the intelligent birds can recognize when a human cheats them of a food reward and will even shun the person for at least a month later. The results of the study are published in the journal Animal Behavior.

The ravens were tested in an experiment of reciprocity. The birds were given a low-quality food item, in this case a lousy piece of bread, and could exchange it with a human for a high-quality food item, a nice piece of delicious cheese. But there was a catch: Some humans tricked the ravens out of any food by taking the lump of bread from the birds and refusing to give them cheese in return, choosing instead to snaffle it in front of them.

Understandably, the ravens were rather affronted by this behavior and felt so cheated that they avoided the people who had tricked them out of the morsel of cheese. The researchers then decided to see just how long this distrust lasted for and tried the experiment again a month later. They found that the ravens who experienced the unfair exchange remembered and thus preferred to do dealings with people who had held up their end of the bargain.

They also got ravens who had not been part of the initial reciprocity trial to watch how the initial ravens responded to the cheaters from a month ago. Interestingly, there was little evidence to show the new ravens took this account, suggesting that the ravens only have a memory for direct reciprocity and not indirect.

In the avian world, the corvids – which include ravens, jays, crows, magpies, and nutcrackers – are some of the most intelligent, with comparatively the largest brain of any bird. Among these clever clogs, the ravens are frequently thought to be top of the pack. They are known to craft tools and solve complex problems, and now it seems that they have some sense of what is fair and unfair.

The researchers think that this ability to recognize when another person is fair or not could have helped the birds evolve their group cooperation. You don’t want to be a member of a flock and contribute to its success if someone else is taking a free ride and not contributing. Everyone needs to chip in.