Aggression and peripheralization in subadult male long-tailed macaques in Singapore

Aggression and peripheralization between adult and subadult male macaques have been postulated as proximate causes for dispersal, but empirical evidence for this relationship is scarce. To investigate the level of aggression and peripheralization experienced by subadult males, we conducted focal animal and scan sampling of two long-tailed macaque (Macaca fascicularis) groups in the highly anthropogenic environment of Singapore’s Central Nature Reserve. We followed two subadult males each in two groups and compared (1) aggression between subadult and adult males and (2) peripheralization measured by (a) greater interindividual distances, (b) more noninteractive behaviors, and (c) fewer interactive behaviors. After 72 focal hours, results suggest varying levels of peripheralization and consistently low levels of aggression among all four males. Data herein call into question the role of aggression in intragroup interactions. Differences in affiliation patterns appear to be core factors in determining the individual degree of peripheralization. Ultimately, strategic choices related to an individual’s place within the natal group (e.g., affiliations, rank of relatives) may be important to cost–benefit assessments; these choices have significant implications in both the short term (i.e., dispersal timing) and long term (i.e., reproductive success). This study is a first step toward understanding macaque behavior in anthropogenic environments; further exploration is needed to anticipate how landscape changes might influence macaque dispersal patterns. Greater understanding will come from recognition that social mechanisms are highly individualized and constantly dynamic, especially for highly cognitive, social species, and in ever increasingly dynamic anthropogenic environments.