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The notion that crows and ravens might reward humans who provide them food motivated the title of the book Tony Angell and I recently published (Gifts of the Crow; 2012 Simon and Schuster). When I first got an email message from a loyal crow feeder stating that he was gifted with candy hearts, twigs, and metal trinkets after offering his birds specially prepared chicken I was dubious. Gary’s story and the various explanations we investigated that might account for it formed an early post to the Avian Einsteins blog. Our conclusion was that either the birds leaving gifts (and there are many instances of this in addition to Gary’s) were mistaken or they were actively rewarding their feeders, perhaps to assure a steady flow of crow chow. I argued that it really isn’t all that unbelievable to think that a bird as smart as a crow or raven might figure out that “if I offer a reward, I will obtain more food.” But, honestly it still seemed like a bit of a stretch. Could wild birds really be that sensitive to the source of food, the motivation of others, and their future wellbeing?
I am delighted to tell you all: Yes! A recent article published by Austrian researchers Claudia Wascher and Thomas Bugnyar demonstrates that crows and ravens understand the concept of exchanging items for a reward and are sensitive to others’ efforts and payoffs (published in 2013, PLoS One 8(2):e56885).
Here is what Drs. Wascher and Bugnyar discovered. Ravens and crows quickly learned to observe a human holding a rock in one hand and a food item—either a highly preferred bit of cheese or a less preferred grape—in the other hand. To get the food, the birds learned to reach through the cage and first grab the stone, take in into their cage, and then return it to the human. Upon successfully exchanging the stone with the person, the bird could then reach out and take the food. They were especially keen to work of cheese, but they even worked (over 70% of the time) for grapes. As they worked they had the opportunity to observe another bird, adjacent to them, working as well. And here is where the researchers discovered just how sensitive crows and ravens were to the actions of their benefactors. A bird’s motivation to work—to exchange the rock with the human for food—diminished under two conditions. If a focal bird saw that its neighbor received food without doing the rock exchange, the bird took longer to exchange or simply refused to exchange! And, if the focal bird saw that its neighbor got cheese for its efforts, but itself only received grapes, again it either took longer to exchange or totally refused to work. Crows and ravens pay attention to what they are given, adjust their work effort to match the payback, and get disgruntled when they see others getting something for nothing or something better than they got for the same effort. This ability to adjust their work to the equity of a reward (as gauged by judging others’ rewards) puts these amazing birds in a class with dogs, monkeys, and humans.
Beyond demonstrating acute cognition, the crows and ravens in Wascher and Bugnyar’s experiments also demonstrated the possibility that their wild brethren could do likewise. The crows, raven, and magpies that we discuss in Gifts of the Crow who leave shiny treasures for the people who feed them are simply doing the wild version of the rock exchange. Clearly these birds can learn to offer a gift for a reward, but in the wild they must do more than understand this relationship. They must initiate the game. This is a step beyond what the experimental birds accomplished, but it is a much smaller step than I originally thought was necessary. Using the experimental results, I conclude that the concept of exchange for reward is easily learned by crows and ravens and that the quality of the reward and perhaps the actions of those offering the reward is also understood. So, to suggest that with this understanding a bird might offer a reward to a valued social partner in exchange for a future meal seems downright reasonable!
I always enjoy reading about a well-designed experiment that demonstrates the mental abilities of birds. Often these experiments have little connection to how the animals survive in nature. But in the case of crows and ravens exchanging rocks for food, I see the cognitive seeds that may underlie a truly remarkable behavior that a few lucky people have observed in the wild. Using their brains to keep us humans working for them may truly be the greatest gift of the crow.
