Causal affordances shape Hornbills' problem-solving strategies

Abstract

Insight--that eureka moment when understanding emerges without trial-and-error--has traditionally been limited to great apes, corvids, and parrots (Byrne, 2016; Emery & Clayton, 2004; Lambert et al., 2019). The vertical string-pulling paradigm, a hallmark test of avian cognition (Jacobs & Osvath, 2015), requires birds to retrieve suspended food by incrementally pulling the string with their bill while securing it with their foot--demonstrating both motor coordination and causal understanding. However, Oriental pied hornbills (Anthracoceros albirostris) present an interesting case due to their unique anatomical constraints--their fused proximal phalanges prevent them from employing the typical foot-assisted string-pulling technique used by other birds. This study challenged six Oriental pied hornbills with two distinct vertical string-pulling problems, each requiring different solving strategies based on their causal properties. Despite their pedal limitations, five of the six subjects successfully solved both problems with remarkable efficiency, achieving solutions within an average of 17.6 seconds of their first encounter with the tasks. Most notably, the successful hornbills immediately employed task-specific biomechanical strategies that directly addressed the causal relationship between the string and the food reward: vigorous shaking movements to dislodge unsecured rewards, versus precise bill-and-tongue manipulation for rewards firmly attached to the string. The hornbills immediate application of causally appropriate, task-specific solutions without prior trial-and-error strongly supports the genuine insight hypothesis rather than associative learning explanations. These findings reveal sophisticated problem-solving capabilities in this previously understudied taxon and contribute valuable evidence to our understanding of convergent cognitive evolution across phylogenetically distant species.