Ecological Adaptation of Silvery Lutung (Trachypithecus cristatus Raffles, 1821) in Coastal Forest Habitat in West Sumatra, Indonesia

Abstract

Core aspects of fundamental primate behavior studies often include activity budgets, feeding habits, and ranging behavior. Understanding the primate behavior provides insights into their adaptive strategies. This study presents quantitative data on the behavior of wild silvery lutungs (Trachypithecus cristatus) inhabiting at Gunung Padang coastal habitat in West Sumatra, Indonesia. It analyzes the activity of these primates with a focus on age-sex differences and monthly changes in their activity budget, emphasizing the relationship between food availability and seasonal changes. Then, this study examines feeding strategies and evaluates ranging behavior, investigating the relationships between activity budgets, dietary composition, and food availability. Gunung Padang, where natural vegetation mixes with plantation, the study utilized direct observation of one group of silvery lutungs (25 individuals) using 10- minute instantaneous scan sampling within 15 months from 2018 to 2021 (614 h). The findings reveal that the group spent nearly half of their daily time resting, suggesting a strategy to conserve energy. The activity budget for each category of activities fluctuated monthly, reflecting changes in resource availability or environmental factors. Notable differences among sex and age classes were observed, which highlight the specific needs and roles of different group members. The lutung also fed on fruits, flowers, and various plant materials which showed they were adaptable in their food selection. A positive correlation between the consumption of mature leaves and ripe fruits with overall dietary diversity, indicating a complex ecological interaction. Conversely, a negative correlation between the consumption of young leaves and both fruits and flowers, suggesting a preference or necessity for young leaves when they are abundant, which affects the consumption of other dietary components. Consumption on flowers of Spathodea campanulata, young leaves of Homalanthus populneus, and unripe fruits of Ficus spp. underscore the importance of certain plants in lutung habitats, suggesting these plants should be a focus in conservation efforts. The annual home range of silvery lutungs was smaller (8.1 ha) compared to other studies on Trachypithecus spp., while their daily travel distance was longer (926 ± 385 m). During seasons with limited food availability, the lutungs likely traveled farther to locate trees with young leaves. Daily travel distance was positively correlated with the percentage of resting time and negatively correlated with the percentages of feeding and moving. Daily travel distance also correlated positively with the proportion of young leaf feeding and negatively with mature leaf and ripe fruit feeding, also dietary diversity. Overall, the ranging behavior of silvery lutungs appears to be linked to a highrisk, highreward strategy, with increased travel distances during food-scarce seasons reflecting the need to search for optimal food resources.