Social organization and male-female relationships

Abstract

Despite their semi-solitary nature, associations among orangutans are more common than expected by chance for most combinations of age-sex classes. Variation in party size is due to variation in food availability or sexual activity, reflecting the two main types of parties encountered in orangutans. Parties may involve mating or are formed around mothers and immatures of various ages, in which social play is the main social activity. Beyond direct association, Sumatran females tend to remain within audible range of the dominant flanged males, using his long calls to adjust their ranging. Females tend to be more philopatric than males, although it is not clear whether males disperse away from their natal range or end up including their natal range within a much larger home range. The accumulating evidence suggests that orangutans live in more than mere neighbourhoods, but in loose communities in which related females form clusters, share a preference for the same dominant flanged male, within whose earshot they tend to remain and whose ranging is more limited. Further study should reveal whether this Sumatra-derived picture also holds for Borneo.