Balancing Reproductive Demands and Seasonal Food Availability: Foraging Strategies of Adult Female White-Headed Langurs in Karst Habitats.

OBJECTIVES: We examined how seasonality and reproductive stage affect foraging behavior in adult female white-headed langurs (Trachypithecus leucocephalus). Because high-quality foods (e.g., young leaves and fruits) become scarce in the dry season, forcing langurs to shift to low-quality mature leaves, we predicted females would increase food intake either by extending feeding bout duration or elevating intake rate. Given the high metabolic costs of lactation, we further predicted lactating females would consume more food than non-lactating females, and that maternal intake would change with infant age. METHODS: Data were collected over 14 months from a habituated group of 12 individuals using focal sampling. For each session, an adult female was randomly selected for observation and video recording; if the focal individual was out of sight for > 5 min, we switched to another visible adult. Videos were used to quantify feeding bout duration, food intake, and intake rate. RESULTS: Adult females had significantly higher intake of young leaves in the wet season than in the dry season, whereas intake of fruits was significantly higher in the dry season. Lactating females showed no significant differences from non-lactating females in feeding bout duration and intake rate, but their intake of young leaves was significantly higher. Infant age (months) did not affect maternal feeding bout traits. DISCUSSION: In the karst habitat, langurs maintain energy balance not by increasing overall food intake, but via dietary selectivity (prioritizing young leaves), seasonal dietary switching (exploiting dry season fruits), and a prolonged lactation period that spreads metabolic costs.