Learned precision tool use in carrion crows.

Tool use is rare in the animal kingdom but relatively common among dexterous generalists such as primates, parrots, and corvid songbirds.¹ New Caledonian (NC) crows, known for their instinctive tool-making abilities, have long intrigued researchers; however, the motor-cognitive skills underlying these behaviors-such as the level of cause-and-effect understanding and precise yet flexible motor control-remain unresolved.^2,3,4,5,6 To investigate how learning shapes these skills, we studied carrion crows, an NC-crow-related corvid species with similar cognitive abilities but no tool-use-specific adaptations.^7,8 We trained three tool-naive carrion crows to use a beak-held stick to retrieve food pellets from a transparent Plexiglas crack in an automated apparatus. Utilizing computational pose estimation,⁹ we tracked the crows' development of stick tool skills over thousands of trials. Our findings demonstrate that tool-naive carrion crows learn to handle tools with impressive skill, achieving dexterity similar to habitual tool users like NC crows. More notably, we observed that all the crows developed efficient, unique, and goal-directed movement patterns. Even after extensive training, the crows retained a remarkable level of flexibility, swiftly correcting errors and adjusting the orientation of the stick to maintain precise alignment. Our findings suggest that reinforcement learning alone can foster skilled tool use in dexterous, cognitively flexible corvids. This implies that only modest evolutionary changes-such as a predisposition to maneuver elongated objects when exploring crevices^7,10-may be needed to transform dexterous generalists into habitual tool users.