Male-male relationships in orangutans

Abstract

Sexually mature male orangutans live in home ranges that are 3–5 times that of adult females and show very high overlap. Encounters among flanged males, while rare, are invariably antagonistic and may lead to injury or death. Their dominance relations are not always transitive, however, producing non-linear hierarchies, probably because they usually meet one on one. Flanged males in consortship with a receptive female frequently chase unflanged males trailing them, but never catch them, so that unflanged males often remain associated with the consort pair. Unflanged males are more tolerant among each other, although attacks also occur. The response of flanged males to long calls they hear depends on their dominance position: the dominant male approaches them, whereas the other males tend to avoid them. There is no conclusive information on the reaction of unflanged males. Data from Sumatra suggest that dominant flanged males and the males challenging them for local dominance were most commonly present in a given study area, suggesting that non-dominant males roamed more widely in search of uncontested access to females.