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A crow uses a stick as a tool to retrieve a piece of food.
Working toward tangible goals can have a positive effect on mood, making people feel happier or more optimistic. A new study found that New Caledonian Crows (Corvus moneduloides) experience a similar effect after tool use.
An international team of scientists from the United States, New Zealand, and Germany investigated whether engaging in complex behavior enhances the mood of crows. First, they developed a way to gauge the birds’ mood. Fifteen newly-caught wild crows were taught that a box placed on one side of a table had a large food reward, while a box on the other side had a small reward. Anticipating a bigger treat, the crows approached the large-reward box more quickly than the small-reward box. The team then placed a box in the middle of the table, creating a condition in which the birds did not know what to expect. The amount of time that crows took to approach the middle box was considered an indication of optimism, with quicker approaches indicating greater hopefulness about receiving a big reward.
The middle box test was then used to judge the crows’ mood after obtaining food from between two pieces of plexiglass, either using a stick as a tool or only their beaks. When the crows used tools, they were on average about ten seconds faster to approach the middle box, compared with when they used just their beaks, suggesting that crows were significantly more optimistic about what might be inside following tool use. The result could not be explained by a sense of accomplishment from the increased effort of tool use—the team also gave the crows an effortful task of retrieving food from four dispersed locations and found that effort was associated with less optimism, not more. “Instead, we think it’s actually an effect of using the tool itself,” said lead author Dakota McCoy of Harvard University. “[The crows] appear to intrinsically enjoy tool use.”
The results hold relevance for those wanting to enrich the lives of captive animals. Complicated activities that are species-specific “may not only occupy an animal’s mind, but give them a better mood,” said McCoy. (Current Biology)