Weaning Age in Yunnan Snub‐Nosed Monkeys: Effects of Interbirth Interval, Seasonality and Sex‐Biased Maternal Investment

Weaning represents a critical developmental milestone in mammals, marking both the termination of maternal nutritional investment and the onset of infant nutritional independence. The weaning age may vary significantly depending on ecological and social conditions for mothers and offspring. Using 10 years of nursing data from provisioned Yunnan snub-nosed monkeys (<i>Rhinopithecus bieti</i>), our results revealed a mean weaning age of 18.16 ± 3.46 months in <i>R. bieti</i>, with variation in weaning age significantly influenced by both interbirth interval (IBI) and weaning season. Regarding differences in nursing investment for different sex offspring, we found no significant difference in weaning age between male and female offspring. However, female offspring received significantly more frequent and longer nursing durations compared to males, while male offspring experienced more frequent nursing refusal. These findings demonstrate that specific behavioural and ecological conditions-including IBI and weaning season-can substantially influence weaning patterns. Our study not only enhances understanding of life history characteristics in extant <i>Rhinopithecus</i> but also provides important insights for interpreting the evolution of unique life history strategies in primates.