An investigation of the auditory perception of western lowland gorillas in an enrichment study.

Previous research has highlighted the varied effects of auditory enrichment on different captive animals. This study investigated how manipulating musical components can influence the behavior of a group of captive western lowland gorillas (Gorilla gorilla gorilla) at Bristol Zoo. The gorillas were observed during exposure to classical music, rock-and-roll music, and rainforest sounds. The two music conditions were modified to create five further conditions: unmanipulated, decreased pitch, increased pitch, decreased tempo, and increased tempo. We compared the prevalence of activity, anxiety, and social behaviors between the standard conditions. We also compared the prevalence of each of these behaviors across the manipulated conditions of each type of music independently and collectively. Control observations with no sound exposure were regularly scheduled between the observations of the 12 auditory conditions. The results suggest that naturalistic rainforest sounds had no influence on the anxiety of captive gorillas, contrary to past research. The tempo of music appears to be significantly associated with activity levels among this group, and social behavior may be affected by pitch. Low tempo music also may be effective at reducing anxiety behavior in captive gorillas. Regulated auditory enrichment may provide effective means of calming gorillas, or for facilitating active behavior. Zoo Biol. 35:398-408, 2016.