New Caledonian crows (Corvus moneduloides) are well-known for their sophisticated tool use. According to a new study, these birds behave optimistically after tool use. The findings, published in the journal Current Biology, raise the possibility that enjoyment may be a fundamental cause in the evolution of tool use and other complex behaviors.
A New Caledonian crow (Corvus moneduloides). Image credit: Jolyon Troscianko.
“What this suggests is that, just the same way we enjoy something like solving a crossword, New Caledonian crows actually enjoyed simply using a tool,” said Dakota McCoy, a graduate student at Harvard University.
“I think it suggests there’s a lot more going on in that little head than we think. They get satisfaction out of doing things they’re good at, have trained for their whole lives, and that they use frequently.”
To understand how New Caledonian crows felt about using tools, McCoy and her colleagues devised an experiment to test how optimistic the birds were feeling.
In the lab, the birds were trained using a small box. When placed on the left side of a table, the box always contained a large reward — three pieces of meat. On the right side, it contained just a scrap of meat, a far smaller reward.
Once the crows understood the difference, the researchers placed the box in the middle of the table. If the birds quickly came to investigate that ambiguous box, it suggested they were optimistic that they would find a large reward. If they waited or didn’t visit the box at all, it suggested they were more pessimistic.
To test how they felt about tool use, the crows were then put through a series of tests over a number of days — one in which they had to use a tool to extract a piece of meat from a box and another in which the meat was readily available.
“But we thought that it might not be that tool use puts them in a good mood, it could be just that they had to work harder,” McCoy said.
“So we added two more conditions. In one the meat was right on the table so there was no effort involved, and in another effortful condition, they had to fly around to the four corners of the room to retrieve each piece of meat.”
The results showed that, following tool use, the birds were much quicker to approach the ambiguous box, and much less enthusiastic after the effortful test compared to the easy test.
“They enjoyed the easy condition. That was no surprise. But the surprise was that, clearly, they don’t just like tool use because it’s difficult. We controlled for difficulty and that wasn’t what was motivating their interest — there is something specific about tool use they’re enjoying,” McCoy said.
“One potential answer for why tool use evolved is because crows are used to picking up objects and caching them. They actually love, when you’re experimenting with them, to pick up your equipment and cache it way up high where you can’t get it,” she added.
“Once crows started using tools the fact that it made them feel good encouraged them to keep at it, refining and developing the behavior further.”
“Maybe crows are just like humans and other primates in that, when they’re doing these complicated actions, they’re reinforced not just by getting a prize out of it, but because they actually enjoy the process itself.”
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Dakota E. McCoy et al. 2019. New Caledonian Crows Behave Optimistically after Using Tools. Current Biology 29 (16): 2737-2742; doi: 10.1016/j.cub.2019.06.080
