Forms, Patterns, and Predictors of Body Contact Between Mothers and Infants in Ngogo Chimpanzees (Pan troglodytes...

Physical contact between mothers and infants is a cornerstone of infant care in primates, providing protection, thermoregulation, and transportation. While previous studies have focused primarily on ventro-ventral and dorso-ventral contact, the diversity of body contact forms and their developmental trajectories remains underexplored. We examined how infant age, sex, maternal parity, and group size influence mother-infant body contact in 37 chimpanzee (Pan troglodytes schweinfurthii) pairs at Ngogo, Kibale National Park, Uganda. We categorized contact into ventro-ventral, ventro-dorsal, lap, low ventral, flank, and sitting beside the mother. Ventro-ventral contact dominated early life and declined steadily with age, while ventro-dorsal and sitting beside the mother contact increased with locomotor competence and independence. Notably, ventro-ventral contact declined well before weaning, indicating that changes in contact form are partly decoupled from nursing trajectories. Lap and low ventral contact were most frequent in infants under 6 months, highlighting their importance for early support and nursing access, while sitting beside the mother emerged as a key intermediate position that may support proximity, exploration, and mother-infant attachment. Infant sex and maternal parity shaped developmental pathways of specific body contact use, and group size influenced both overall contact and ventro-dorsal contact rates, suggesting sensitivity of mother-infant interactions to social context. Together, these findings demonstrate that shifts among multiple forms of body contact reflect interacting developmental, maternal, and social processes, underscoring the importance of considering diverse contact forms to understand infant care and developmental transitions in primates.