Social relationships of immigrant and resident female mountain gorillas, II: Relatedness, residence, and relationships between females.

Female transfer is common in mountain gorillas, but most adult females reside with female relatives for at least some of their lives. In four mountain gorilla social groups, co-resident relatives had higher rates of affiliative interaction and lower rates of aggressive interaction, and were more tolerant of each other, than non-relatives. These differences were greater for maternal than for paternal relatives. Non-relatives typically had few affiliative interactions, but some (mostly but not entirely long-term co-residents) had friendly relationships. Females showed reciprocity in affiliative behavior. Long-term residents in two groups maintained less tolerant relationships with more recent immigrants than with each other and than did most pairs of immigrants. The effects of relatedness and residence status on relationships may sometimes be complementary because both factors can lead to similar reproductive interests. A potential exists for some resemblance between female-female social relationships in mountain gorillas and those in female-bonded primate species. However, even female relatives usually spend little time interacting socially with each other, and the benefits of relationships with males outweigh those of relationships with other females. © 1994 Wiley-Liss, Inc.