Do ravens hold a grudge?

Many studies have already demonstrated the intellectual abilities of corvids, such as crows, magpies, and ravens. A scientific team from the University of Vienna (Austria) and the department of cognitive sciences at Lund University (Sweden) tested the memory capacities of crows. By subjecting them to a rather unusual experiment, the researchers discovered that ravens are rather spiteful creatures…

J.J.A. Müller and colleagues tested the memory of nine ravens in an exchange paradigm with humans (reciprocity). Laggie, Horst, Louise, Nobel, and the other ravens had the opportunity to exchange a low-quality food (bread) for a high-quality food (cheese); experiments have shown that crows prefer cheese to bread. The crows were trained on this exchange, but at a certain point, the experimenters decided to deliberately cheat, undermining the reciprocity.

During the first phase, each crow participated in the exchange paradigm with two different experimenters during two exchange sessions at 3-hour intervals. During the first session, the birds had a fair partner that always traded the bread for cheese. But during the second session, the crows interacted with an unfair experimenter that took their bread but offered nothing in return (they even ate the cheese in front of them!) Keep in mind that the exchange partners were all women and that the crows had had no prior social experience with them. Moreover, during thus “seeding” phase, other crows were in attendance to observe the "exchanges." Once this phase was complete, the test phases began.

The crows were tested individually. They were given the choice between the “fair” experimenter, the “unfair" experimenter, and a third “neutral” experimenter. Here's what happened: the bird received a piece of bread from a trainer, which he could then exchange with one of the three experimenters; the experimenters offered to trade by presenting the empty palm of their right hand and offered a piece of cheese in their left hand. As in the “seeding” phase, the “fair” experimenter traded the cheese, and the “unfair” experimenter ate it (the cheese, not the crow!). The “neutral” experimenter gave the bread back (which gave the crow another chance to trade). Fifteen consecutive trials were conducted during the two sessions of the test, carried out two days and one month after the "seeding."

The results show that the ravens that had directly participated in the exchanges (fruitful and fruitless) were more likely to interact with the fair experimenters rather than with those who had tricked them, even after one month. The crows can thus rely on their memory after a single interaction sequence. However, the crows that observed the experiment made no distinction between experimenters, even if those crows (among the observers) who had had a first-hand experience with the paradigm appeared more likely to prefer the fair experimenter. The observer results weren’t statistically significant, but they do tentatively suggest a capacity to remember indirect reciprocity.

Conclusion: don’t trick ravens, they’re likely to hold a grudge!
Source: J.J.A. Müller, J.J.M. Massen, T. Bugnyar, M. Osvath, “Ravens remember the nature of a single reciprocal interaction sequence over 2 days and even after a month,” in Animal Behaviour, vol.128, June 2017.


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