Understanding Proboscis Monkeys (Nasalis larvatus Wurmb) Behaviour through Instantaneous Observation to Support Sustainable Mangrove Ecosystem in Curiak Island, South Kalimantan

This study aimed to observe the behavior of proboscis monkeys (Nasalis larvatus) in the mangrove area of Curiak Island to support sustainable mangrove ecosystem. Instantaneous observations were conducted on the largest group in the area from a 45-meter distance over 16 days, between 07.00 and 11.30 am. One individual was observed each day from arrival until return to the forest. Sixteen individuals were observed: 5 adult males (>7 years), 5 adult females (2-7 years), 3 juveniles (1-2 years), and 3 infants (<1 year). Behaviors were categorized into total activity, eating bananas, eating leaves, resting, and other activities. Most monkeys visiting the observation area belonged to the Alpha group and arrived shortly after bananas were placed. Adult males stayed the longest (51 minutes), followed by adult females (39 minutes), juveniles (37 minutes), and infants (33 minutes). Males spent more time eating bananas, while females rested longer. Juveniles and infants ate more leaves and engaged in other activities like traveling and social interactions. It is concluded that male proboscis monkeys spend considerable amount of time in the feeding area and fed various plant. This result can be used as an indicator to asses the important role of proboscis monkeys toward mangrove ecosystem. © The Authors, published by EDP Sciences, 2025.