Sound Guides Object Size Choices in African Penguins Through Pitch–Size Association

The brain's ability to associate information from different sensory modalities, known as cross-modal integration, is crucial for forming a coherent perception of objects and events. When such associations follow systematic and predictable patterns, they are referred to as cross-modal correspondences. Humans, for example, tend to associate large objects with low-pitched sounds and small objects with high-pitched sounds, a phenomenon known as pitch–size cross-modal correspondence. This phenomenon has been documented in several vertebrate species, yet direct experimental evidence in avian species remains comparatively limited. Here, we tested African penguins using a preferential choice paradigm in which individuals chose between two cubes of different sizes after hearing either a high- or low-pitched sound. Following passive exposure to congruent pitch–size pairings, penguins chose larger objects following low-pitched sounds and smaller objects following high-pitched sounds, indicating that auditory pitch guided their visual size choices. Given that individuals were pre-exposed to a limited set of pitch–size pairings, this effect may reflect either a preexisting bias consistent with cross-modal correspondences or the generalization of a learned association. Nevertheless, these findings demonstrate that penguins can integrate auditory and visual information to guide their behavior and generalize a systematic pitch–size relationship across sensory dimensions.