Maternal Decision-Making in Non-Mother Caregiving Negotiation for Infants in Black-and-White Snub-Nosed Monkeys (Rhinopithecus bieti).

Allomaternal care, or caregiving by non-maternal individuals, is prevalent in primates, yet few studies have explored the role of maternal consent and decision-making during this process. This study introduces the concept of "non-mother caregiving negotiation", highlighting the mother's primary role in deciding on non-maternal caregiving. This study focuses on a semi-provisioned breeding band of black-and-white snub-nosed monkeys (Rhinopithecus bieti) in the Xiangguqing area of the Baimaxueshan National Nature Reserve. We investigated how non-maternal females employ signaling behaviors to express their desire to care for infants and how maternal consent is achieved. Our study found that non-maternal females use specific behaviors, such as grooming the mother, gently touching, kissing, grooming the infant, or softly pulling the infant closer, to signal their interest. Mothers respond consistently to these signals, but their decisions to allow caregiving largely depend on the infant age and the caregiving experience of non-maternal females. As infants grow older, mothers become more likely to permit caregiving, particularly from females with prior caregiving or birthing experience. During each caregiving event, infants were often transferred among multiple caregivers, with infants being passed an average of 2.2 times by 2.5 caregivers within the same caregiving event. Additionally, when infants are under the care of non-maternal females, mothers rest less and spend more time on feed, social, move and other activities, thus reducing their own caregiving costs while enabling non-maternal females to gain caregiving involvement. Consequently, non-mother caregiving negotiation emerges as a behavior shaped by communicative interactions between mothers and non-maternal females, offering new insights into caregiving dynamics in primates and illuminating caregiving behaviors in both primate and human societies.