Social aging in male and female Barbary macaques

Abstract

Aging brings about notable changes in sociality, with an increasing focus on essential partners in both humans and nonhuman primates. Several studies have shown that older nonhuman primates have fewer social partners and shift their types of interactions. The majority of these studies, however, involved only female individuals. Much less is known about the trajectory of social aging in males. We collected 2180 h of focal observation data in a large age-heterogeneous sample of 34 male and 50 female Barbary macaques (Macaca sylvanus; age range 5-30 years) living in two social groups at the outdoor enclosure at La Forêt des Singes in Rocamadour (France). To track age-related changes in social engagement of both sexes, we used classical behavioral and social network analysis to measure age-related variation in the number of partners, the frequency of affiliative interactions, and the position in the social network (eigenvector centrality and local clustering coefficient). We found that females were more central in most social network metrics than males, that is, had more social partners and were more engaged in affiliative interactions than males. We did not find notable sex differences with age: both sexes showed a similar decline in social activity and energy-demanding activities like jumping or running. Our results thereby extend our knowledge of older nonhuman primates' social life and emphasize that age can have a similar impact on female and male social behavior.