Nursing behavior of infant pigtail monkeys (Macaca nemestrina): preferences for nipples

Nursing behavior of 56 singleton infant pigtail monkeys (Macaca nemestrina) was monitored. Infants over 1 mo. of age showed strong preferences for one of their mothers' nipples, while few infants less than 1 mo. old did so. The infants which had the lowest birthweights for each sex showed no clear preference even though they were older than 1 mo. A trend toward lateral preference (for the right nipple) was identical for male and female infants. Analysis of the development of preference for nipple may provide useful information of assessing development progress.