How do male interactions with infants affect mothers and infants in Barbary macaques (Macaca sylvanus)?

Abstract

In Barbary macaques, males handle infants to regulate relationships among themselves. Previous studies of male infant handling have focused on its function from the perspective of male handlers, while the effects on the mother and infants have not yet been considered. Since infant care is costly, being unencumbered by their infants may enable mothers to spend more time feeding. However, mothers may also experience elevated anxiety when separated from their infants. Since handlers may be less restrictive than mothers, infants may benefit from a greater number of interactions with others and higher rates of independent locomotion and exploration. I assessed the immediate behavioural effects of male infant handling on the mothers and infants involved. I studied a semi-free ranging population of Barbary macaques at La Montagne des Singes, Kintzheim, France. First, I observed behaviours of mothers when they were with their infants and when male group members handled them. I compared the rates of self-directed, grooming and vigilance behaviours and the proportion of time mothers spent feeding. Second, I observed infants when with their mother and when with male handlers. I investigated the infants’ rates of independent locomotion, number of social partners and exploratory behaviours and distress behaviours, such as squealing. I analysed the data with a negative-binomial GLMM. When they were away from their infants, mothers exhibited greater rates of self-directed behaviours, vigilance and groomed others for longer compared to when they were with their infants. Mothers did not differ in the duration of time they spent feeding when away from than when with their infants. Infants exhibited greater rates of distress behaviour when with males than when with their mothers. Infants did not differ in the rate of independent locomotion or exploration between conditions or interact with more individuals when with the male than their mother. These results show that in a provisioned group of macaques, mothers and infants do not appear to directly benefit from male infant handling but may pay a cost. Infants and mothers were distressed when separated from each other. Mothers and infants may gain long-term benefits such as agonistic support, access to resources and earlier infant weaning from associating with males in the group.