Continuity of affiliative relationships among infants and juveniles in a free-ranging group of Japanese monkeys (Macaca fuscata).

5 infants were observed during the first 13 mo. after birth in a free-ranging group of Japanese monkeys (Macaca fuscata) to examine whether they maintained relatively frequent affiliative relationships with particular immature individuals. The number of immature affiliative partners rapidly increased from the first 3-mo. period after birth to the second 4-mo. period after birth, and the infants thereafter maintained affiliative relationships with particular individuals, mostly same-aged infants, at least in the second half of their first year. These findings show that infants were likely to interact with a larger number of different animals in the early stage of development, and thereafter selected particular individuals with whom they maintained affiliative relationships. The effects of sex on the selection of these long-term partners are also discussed.