A crow using a tool takes a block of meat from an apparatus

A New Caledonian crow uses a stick to reach some meat. Such activity gives the birds a more optimistic outlook. Credit: Dakota McCoy

Animal behaviour

To lift a crow’s mood, give it a toolkit

Clever crows are more cheerful after wielding simple instruments.

Much like humans, crows enjoy using their brains — and become more optimistic when they have the chance to employ tools.

New Caledonian crows (Corvus moneduloides) are unusually intelligent birds that can craft sticks into hooks, which the birds then use to retrieve insects from logs. Dakota McCoy at Harvard University in Cambridge, Massachusetts, and her colleagues trained 15 wild crows to recognize that a box contained a small reward when placed at one end of a table, and a larger reward when placed at the other end. Trained crows moved faster towards boxes promising big rewards than to those containing small ones.

The researchers also presented the birds with a box in an intermediate position on the table. Crows that had recently used tools to retrieve food moved quickly towards the box. But birds that had not just wielded tools approached the box more slowly, suggesting they had a more negative attitude.

The researchers suspect that tool use primed the birds’ brains to be more optimistic.