Crows are one of the few animals known to make tools. New Caledonian crows in particular stand out for manufacturing multiple complex tools and refining their designs. A study in Current Biology led by PhD candidate Dakota McCoy (Haig Lab) suggests the crows do it because it makes them happy. McCoy devised an experiment to test how optimistic the birds were feeling making and using tools. The crows were trained using a small box that when placed on the left side of the table contained a large reward. And, when on the right side, contained a small reward. Once the crows understood the difference the box was placed in the middle of the table. If the crows quickly came to the box it suggested optimism, if they waited or didn't visit it suggested pessimism.
An “effortless” condition placed a reward directly on the table and an "effortful" condition where the crows had to fly to the four corners of the room to retrieve the reward. The results showed the birds were much quicker to approach the ambiguous box after using the tools, and less enthusiastic after the effortful test compared to the easy test. "What this suggests," said McCoy. "Is that, just the same way we enjoy something like solving a crossword [puzzle], they actually enjoyed simply using a tool." To improve the emotional states of captive animals, we should give them complex, species-specific enrichment. The study was covered in The Harvard Gazette.