Adult male replacement inMacaca fascicularis of East Kalimantan,Indonesia

This report on wild-ranging crab-eating macaques in East Kalimantan, Indonesia, describes male replacements for the first time in this species. A replacement at the alpha rank by an immigrant adult male was seen in this multimale troop during each year of the 20-month field study. The data show considerable variation in the process and outcome of social change. Adult male immigrants contested the alpha rank, whereas subadult male immigrants did not. The first replacement took 2 days, whereas the second one took 1 month. In the first replacement four males and 10 other residents left the troop. In the second replacement one of the two adult males was successful in immigrating when he replaced the resident male of his alpha rank, but the deposed alpha male was not evicted from the troop. Existing models of the causes of replacement (such as high density or human disturbance) and of the causes of infanticide are not supported by these data. Infanticide by immigrating males was not observed despite the apparent presence of the postulated circumstances conducive to infanticide.