Developmental Changes in Feeding Behavior and Maternal Influences in Wild Javan Gibbons (Hylobates moloch)

Abstract

Immature primates acquire skills through social learning from more experienced individuals. The needing-to-learn hypothesis posits that prolonged juvenility evolved to support such social learning under social and ecological challenges. In particular, feeding complexity—food requiring complex skills—poses challenges. Despite prolonged juvenility, the development of feeding behavior and social learning in gibbons remain poorly understood. We examined the feeding behavior of four offspring (aged 9 to 50 months) and their mothers in three habituated groups of wild Javan gibbons (Hylobates moloch) in Gunung Halimun-Salak National Park, Indonesia (December 2019 to January 2022). We analyzed the effects of immature age and food size on 1) immature’s dietary breadth and diet similarity with mothers, 2) daily proportion of time the immature spent feeding and co-feeding with mothers, and 3) responsibility for maintaining close proximity to mothers during feeding, using the Hinde index. Immature dietary breadth increased with age, whereas diet similarity with mothers decreased with age. Daily feeding time increased with age, but this increase was weaker for medium than for small food. Co-feeding time with mothers decreased with age, with a significantly stronger decline for medium than for small food. Although immatures became less responsible for maintaining proximity to mothers during feeding with age, they stayed closer when feeding on large than on small food. Our results showed developmental changes in feeding behavior and suggested maternal influences on information acquisition in wild Javan gibbons, highlighting how social and ecological factors shape feeding development and potential social learning in immature primates.