The Formosan rock macaque has a multimale-multifemale social system, with groups averaging around 45 individuals occupying partially-overlapping territories (5) (7). However, the recent decline in numbers has meant that groups are often much smaller, typically ranging between two and ten individuals, and may more closely resemble a unimale system (4) (5). While females remain in their natal group, existing within a female hierarchy, males disperse shortly after adolescence, at around five years of age (5) (7). However, relatively low-ranking females have been observed splitting from their natal group to form new troops where they may find higher status. Low-ranking sub-adult and old adult males within a troop are peripheralised by the dominant alpha male, and often form coalitions. Most challenges for the alpha-male position are made during the breeding season, when competition for access to sexually receptive females is fierce (7).
The breeding season is between November and January, with births occurring from April through to June, peaking from mid-April to mid-May (5) (7). Females start to breed at between four and five years of age (7), after which they usually produce a single offspring every other year, with older females giving birth every year (5). Gestation lasts around 165 days and, in most macaques, nursing lasts about a year, with the majority of parental care provided by the mother. Young are usually completely independent after two years, although females often retain life-long associations with their mother and other female kin (5).
Formosan macaques are a diurnal, ground-dwelling species, comfortable in areas with few or no trees. A variety of foods are consumed, including fruits, leaves, berries, seeds, buds, young shoots, insects and small vertebrates, and these macaques reportedly also raid crops (5).