Infant cross-fostering between Japanese (Macaca fuscata) and rhesus macaques (M. mulatta).

Cross-fostering of infant rhesus macaques between unrelated females has become a routine management strategy at the California Primate Research Center. In order to study the effect of environmental factors on vocal development, we extended this procedure to offspring exchange between two different macaque species living in small social groups. A total of four neonatal Japanese and rhesus monkeys were fostered onto mothers of the other species. Six attempts were required, for an overall success rate of 67%. However, two of the adoptions involved the same foster mother, and both rejections occurred with the same female. The cross-fostered individuals gained weight normally in the first year of life and did not require any hospital treatment. These results indicate that raising nonhuman primate infants with members of a different species can be a viable means of altering species-typical experience without sacrificing essential aspects of maternal care, socialization, and psychological well-being.