at around the time of puberty (Dittus 1980). In contrast, females spend their entire lives in their natal troop. The sex ratio of adults is typically female-biased. This has been attributed in part to the mortality associated with adolescent male emigration and in part to the longer developmental periods of males. Most social groups usually move through their habitat as a single large troop, but some flexibility in forming subgroups can be seen.

Whereas that general pattern applies to most macaques and baboons, some exceptions should be noted. Hamadryas baboon troops are divided into one-male units (an adult male with several adult females and their offspring). Males actively ''herd" their females, but males of several of these units will act together to repel predators or intruders. Furthermore, a large loose troop structure can be discerned during the evening, when several bands are found in proximity on cliff faces.

Geladas also form one-male units, but males do not herd females. Unlike hamadryas baboons, in which one-male units disperse during the day, gelada units disperse at night and can form large feeding herds on days when feeding conditions are favorable. The social organization of the mandrill and drill are less well known, but basic one-male units have been suggested for these forest-floor dwellers.

Guenons, with the exception of vervets, and patas monkeys generally live in small one-male units. During the breeding season, males might temporarily enter some breeding groups, but, in patas monkeys at least, other males are generally found in all-male bands. Talapoins typically live in large social groups consisting of many adults of both sexes. In captivity, females might dominate males when not in breeding condition, and new males might be attacked by females.

The presence of strong matrilines is characteristic of groups of macaques and baboons in expanding populations, but strong matrilineal subgroups might not be universal. They are not readily detected in declining populations or in those in equilibrium, and evidence of strong matrilineal organization is not found even in expanding troops of sooty mangabeys (Cercocebus torquatus atys). The social organization of the various mangabey species is not yet well described.

Colobine monkeys generally live in one-male units with other males living in all-male bands. Colobus badius (red colobuses) and Rhinopithecus (snub-nosed langurs) form multimale troops of somewhat larger size. Some variation is also noted among Presbytis entellus (hanuman or sacred langur), in which multimale troops might exist temporarily or more permanently in some habitats.

Many African monkeys form polyspecific associations in the wild, and mixed-species groups of guenons have been maintained in captivity without adverse consequences. The high prevalence of simian AIDS viruses in African monkeys, however, argues against mixing them with Asian species. Macaques in particular appear to be highly susceptible to such infections. Different species of macaques will also readily hybridize when mixed-species pairs are formed; however, even though compatible pairs tolerate each other, macaques generally do



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