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

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 behavioral 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 non-invasive eye-tracking method, we investigated if titi monkeys display a visual partner preference. We presented adult titi monkeys with ten static slides showing two conspecific faces side-by-side: either (a) their partner's face and a stranger's face or (b) two strangers' faces. Face side was counterbalanced, and slide presentation order was randomized, across all subjects. We present five looking behavior outcome measures for a study of 40 titi monkeys. We found no evidence of a visual preference for still photos of one's pair mate, but we did find that age, pair tenure, and parenting experience predicted looking behavior. Animals with longer pair tenures spend a longer duration looking at facial images. Younger animals looked at the screen for the first time faster, spent a shorter duration 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 for a greater duration and greater number of times than animals without parenting experience. This study is the first to characterize social looking in a pair-bonded monkey.