DYNAMICS OF FISSION IN A WILD BARBARY MACAQUE GROUP (MACACA-SYLVANUS)

We studied the dynamics of a group of Barbary macaques (Macaca sylvanu s) in Algeria from March 1983 to November 1989. Troop fission began in autumn 1987, when group size had more than doubled, to include 76 ani mals. We observed 11 temporary splits of this group during the mating seasons of 1987 and 1988. The process was interrupted during the 1988 birth season. In June 1989, fission resumed and ended with the formati on of three independent groups that included 50, 24, and 13 individual s. Adult females played an important role in the process of fission. T hey initiated the rapid formation of two, and later three, coherent nu clei, distributed in two or three bisexual subgroups; on several occas ions these nuclei also formed subgroups without any adult males. Adult males remained together in a single nucleus for longer periods of tim e than females did. However, during fission, 35% (N = 20) of resident males emigrated to neighboring groups, while 11 strange males immigrat ed into the focal group; over 6 years, 57% of the male transfers occur red after the beginning of the process. After group fission, maternall y related individuals lived together in the new groups. The majority o f resident males remained with the largest of the three groups, while most of the immigrant males were in another group. The third group inc luded a single adult male. Possible factors that induce group fission are discussed.