the alpha male) leads the group to easily monopolised resources. The group usually follows, even though many subordinate members cannot gain access to that particular resource. As in morning dispersal, the inclination of group members to follow the leader is positively associated with social interactions with that dominant individual. Collective foraging behaviour, with many individuals taking advantage of the same resource at once, has also been observed. However, this behavior can be chiefly attributed to shared dietary needs rather than social affiliation. Pregnant females, who share similar dietary needs, are more likely to synchronise their behaviour than fertile females. Foraging synchronization decreases in areas with lower food density. Adoption Adoption behaviour has been observed in chacma baboons. Orphaned baboons whose mothers have died or disappeared are often too small to care for themselves. In one study of nine natural orphans and three introduced orphans, all but one orphan were adopted by another member of the troop. The individual that was not adopted was 16 months old, four months older than the next oldest orphan, and was old enough to survive on its own. Adoption behaviour includes sleeping close to the orphaned infant, grooming and carrying the orphan, and protecting it from harassment by other members of the troop. Both males and females care for infants, and care does not depend on the infant's sex. Additionally, nearly all caregivers are pre-reproductive, only four or five years of age. The two major theories explaining this behavior are kin selection, in which caregivers take care of potentially related orphans, and parental practice, in which young baboons increase their own fitness by using an orphan to practice their own parenting skills. Friendship Males and female chacma baboons often form relationships referred to as "friendships". These cooperative relationships generally occur between lactating females and adult males. The females are believed to seek out male friendships to gain protection from infanticide. In many baboon species, immigrant alpha males often practice infanticide upon arrival in a new troop. By killing unrelated infants, the new male shortens the time until he can mate with the females of the troop. A female with dependent offspring generally does not become sexually receptive until she weans her offspring at around 12 months of age. However, a mother usually becomes sexually receptive shortly after the death of her offspring. This protection hypothesis is supported by studies of stress hormones in female baboons