Others observe that while they sleep in trees, they forage on the ground during the day. Males leave their birth group and try to find another troop where they try to replace the high-ranking males there. These events are very aggressive and combatants are usually injured. Females remain in their birth group and there is a hierarchy among them which passes on to their offspring. Offspring of higher ranking females have a better chance of survival, through better access to food and less aggression being directed at them.
Troops are highly intolerant of each other.
When two troops meet there is a great deal of aggression, loud calls and branch-bouncing. In these encounters, the troops are led by the alpha male. Single young, twins rare. Gestation 160-170 days. Females mature in 4 years, males in 6 years.