Postural Infant Carrying Adaptations by Wild Eastern Chimpanzees ( <i>Pan troglodytes schweinfurthii</i> ) With Limb Disabilities

Wild primates can become disabled due to congenital disabilities, illness, or injuries from falls and traps. Given their substantial behavioral flexibility, individuals are often able to adapt locomotion and foraging techniques to their needs, but likely incur increased energetic costs. For disabled primate mothers, the combination of altered locomotion, lactation, and infant carrying could pose a substantial energetic challenge that requires specific accommodation. Here, we describe the postural modifications for infant carrying used by five eastern chimpanzee (Pan troglodytes schweinfurthii) mothers with significant limb disabilities caused by snare injuries and compare their technique to non-disabled mothers in the same community. We describe shifts in ventral and dorsal infant carry location, as well as additional support provided to infants. Disabled mothers had altered preferences towards specific infant carrying styles and positions, and novel carrying positions not seen in non-disabled mothers. We suggest disabled chimpanzee mothers use postural adaptations to mitigate the energetic costs of infant carrying while disabled, shifting their infants' weight to an individually specific position. We discuss the plasticity of infant carrying, with individual variation present in both disabled and non-disabled mothers. We highlight that this plasticity is not unlimited, and that certain types of limb disability appear to have a substantial impact on reproductive success.