Task affordances shape hornbills' problem-solving strategies

Innovative problem-solving in birds has traditionally focused on corvids and parrots, but growing evidence shows that many other bird species are also capable of such feats. The vertical string-pulling paradigm, a hallmark test of avian cognition, requires birds to retrieve suspended food by incrementally pulling the string with their bill while securing it with their foot, demonstrating sensorimotor flexibility and the capacity to perceive some of the task's properties. However, Oriental pied hornbills (Anthracoceros albirostris) present an interesting case due to their distinctive foot morphology; their fused proximal phalanges may limit their ability to employ the typical foot assisted string-pulling technique used by other birds. In this study, six hornbills were presented with two string-pulling tasks, each requiring a different approach. Despite their anatomical constraints, five birds solved both problems on their first encounter, with average solution times under 18 s. Strikingly, individuals immediately deployed distinct and appropriate strategies: vigorous shaking to dislodge unsecured rewards and coordinated bill-and-tongue manipulation for secured ones. These rapid, flexible responses suggest that hornbills are highly sensitive to task properties and capable of adjusting their behaviour based on both environmental structure and their own morphology.