Age, pair tenure and parenting, but not face identity, predict looking behaviour in a pair-bonded South American primate

Social bonds are crucial to many animal species. To maintain these bonds, individuals must be able to differentiate the identity of conspecifics. Pair-bonding primates, in general, maintain close bonds with their selected mate. Little is known about visual preferences of pair-bonded primates. To characterize visual preference for images of familiar and unfamiliar faces, we assessed visual attention in coppery titi monkeys, Plecturocebus cupreus . Coppery titi monkeys, like many other pair-bonding species, show a behavioural partner preference when placed in a partner preference paradigm and maintain greater durations of physical proximity to their pair mate compared to an unfamiliar stranger. Using a previously validated noninvasive eye-tracking method, we investigated whether titi monkeys display visual partner preference. We presented adult titi monkeys with 10 static slides showing two conspecific faces side by side: either (1) their partner's face and a stranger's face, or (2) two strangers' faces. Face side was counterbalanced, and slide presentation order was randomized, across all subjects. We present five looking-behaviour outcome measures for a study of 40 titi monkeys. We found no evidence of a visual preference for still photographs of one's pair mate, but we did find that age, pair tenure and parenting experience predicted looking behaviour. Animals with longer pair tenures spent more time looking at facial images. Younger animals looked at the screen for the first time faster, spent less time looking and looked fewer times at the stimuli compared to older animals. Parenting status positively predicted fixation count, total visit duration and visit count, such that parents with more experience looked at the stimuli longer and more times than animals without parenting experience. This study is the first to characterize social looking in a pair-bonded monkey. • We investigated whether titi monkeys display visual partner preference. • We presented static slides of the pair mate vs a stranger or two strangers. • We found no evidence of a visual preference for one's pair mate. • Parents with more experience looked at stimuli longer and more times. • Age predicted shorter durations of looking.