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, she said, 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,” McCoy said. “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.”

While it’s impossible to say for certain exactly what the birds were feeling, McCoy said her study is far from the first to attempt to gauge what effects animals’ moods.

“Many people have done studies about what kind of mood animals are in … but the research to date has almost exclusively been on captive animals, and what kind of circumstantial changes can improve their mood,” she said. “Many people have shown that animals’ mood improves if you do something like give them a larger cage, but this study shows that animals also have a better mood if you give them complex, fun tasks to do.”

McCoy, who is a student in the Graduate School of Arts and Sciences, said that she hopes to see the findings of the study applied to improving the lives of animals in captivity.

“Our findings suggest that one way to improve the welfare of captive animals is to give them complex, species-specific enrichment where they’re using skills they have … to achieve goals instead of just receiving passive enrichment,” she said. “We’re far from a world where we don’t have animals in captivity … but they could live a much more enriching life if they’re housed socially and given fun tasks to solve.”

This research was supported with funding from the Department of Defense, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship, a Theodore H. Ashford Graduate Fellowship, a Royal Society of New Zealand Rutherford Discovery Fellowship, a Prime Minister’s McDiarmid Emerging Scientist Prize, and the Max Planck Institute for the Science of Human History.