Mobile surrogate mothers and the development of exploratory behavior and radius of action in infant long-tailed macaques (Macaca fascicularis).

One of the effects of rearing young monkeys on surrogate mothers is a delay in the development of exploratory behavior. An important question is which difference between mother and surrogate mother caused this delay. We hypothesized that the mothers' carrying the infant through the environment promotes the development of exploratory behavior and the radius of action of infant macques. Using surrogate mothers, we reared 9 infants in a peer group with immobile surrogates and 10 infants in another peer group with mobile surrogates. During the 3rd to the 6th month, we observed each infant for 30 min weekly, collecting observational data on several behavioral parameters and on time spent in several areas in the cage. Results showed that exploratory behavior and an increase in radius of action developed more rapidly in the mobile-reared infants.