Abstract
Mean gestation for seven free‐ranging Tana River crested mangabeys (Cercocebus galeritus galeritus) is 180 days (SE = 4.49). All females showed postconception sexual swellings after the first 2 months of pregnancy, and two of the seven copulated with males at this time. One birth was observed; observations of a second infant began less than 1 hr after birth. Details of parturition are given, with responses of group members to the events. Adult and juvenile females showed more sustained interest in the new infants than adult or juvenile males.