Crows are not only clever but also revel in their cleverness, a new study suggests.

The oft-cheeky birds were found to be behaving more optimistically after using tools, according to recent paper published in Current Biology and co-authored by Dakota McCoy, a graduate student working in the lab of David Haig, George Putnam Professor of Biology.

“What this suggests is that, just the same way we enjoy something like solving a crossword, they actually enjoyed simply using a tool,” McCoy said. “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.”

For example, New Caledonian crows are known for manufacturing multiple complex tools and regularly refining their designs.

McCoy and colleagues devised an experiment to test how optimistic crows felt after using tools.

“We do have subtle ways to test mood, and the classic paradigm is a glass half filled with water,” she said. “Someone who is feeling pessimistic will interpret it as half empty, while an optimistic person will see it as half full.”

The crows were trained in lab using a small box. The box always contained a large reward — three pieces of meat— when placed on the left side of a table, and just a scrap of meat, if placed on the right side.

Once the crows figured out the difference, 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,” according to The Harvard Gazette.

The crows were then put through a series of tests 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.”

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.”