Silence is Golden: Auditory Preferences in Zoo-housed Gorillas.

Enrichment is presented to improve the welfare of captive animals but sound is frequently presented with the assumption that it is enriching without assessing individuals' preferences. Typically, presented sounds are unnatural and animals are unable to choose which sounds they can listen to or escape them. We examined preferences of three zoo-housed gorillas for six categories of sound. The gorillas selected unique icons on a computer touchscreen that initiated brief samples of silence, white noise, nature, animal, percussion, and electronic instrumental sounds. Following training, gorillas selected each sound paired with silence (Phase 2), each sound paired with each other sound (Phase 3), and one sound among all other sound categories (Phase 4). Initially, a single sound was associated with each icon, but additional exemplars of the category were added in phases 5-8. Preferences were generally stable and one gorilla showed a strong preference for silence. Although there were individual differences, a surprising general preference for unnatural over natural sounds was revealed. These results indicate the importance of assessing preferences for individuals before introducing auditory stimulation in captive habitats.