Maternal aggression by lactating group-living Japanese macaque females

This study analyzed the influence of lactation on aggression by group-living Japanese macaque females. Data collected during 268 hr of observation showed that lactating females exhibited much more aggression than did females in any other reproductive condition under investigation. This postpartum aggression showed distinctive features in terms of time course during lactation and target selectivity but it was not characterized by a higher intensity and severity. Aggression increased progressively during the first 6 weeks of lactation, reached its highest levels between 7th and 9th weeks postpartum, and thereafter diminished. The relative percentages of threat, chase, and physical attack did not change with the reproductive condition. Lactating females were selective in their choice of targets, with young females being the recipients of nearly 90% of the total of their aggression.