Abstract: Social recognition among familiar unrelated lambs was assessed in a series of tests. Lambs and their mothers were housed together in small groups for 1 week (Original groups; O) then reorganized into new groupings (Recent-groups; R) for the remainder of the experiment. During test series 1, lambs that were paired with a familiar O-group partner, from which they had been separated for 5 days, emitted fewer distress bleats than did those tested with an unfamiliar partner. This same effect was not evident when the test was repeated several hours later, indicating that the animals had become habituated to the testing procedures. Two days later, when given the choice between an O- versus a R-partner (test series 2), lambs did not display a preference for either of the stimulus lambs. However, in an additional two-choice test (test series 3) the subject lambs responded discriminatively to a recent familiar partner that was simultaneously present with an unfamiliar lamb. Overall, the results suggest that lambs are capable of developing discriminative relationships with age-mates from different sub-groups, and that such social discrimination persists over a separation period lasting at least several days. It is not clear whether lambs recognize several individual conspecifics per se or discriminate between members of higher order social categories (e.g. familiar versus unfamiliar individuals). Proximal and distal social discrimination may be mediated by different combinations of sensory modalities.

Abstract: Eyes play an important role in communication amongst humans and animals. However, relatively little is known about specific differences in eye morphology amongst primates and how these features might be associated with social structure and direction of gaze. We present a detailed study of gazing and eye morphology-exposed sclera and surrounding features in orangutans. We measured gazing in rehabilitating orangutans in two contexts: interspecific viewing of the experimenter (with video camera) and intraspecific gazing (between subjects). Our findings show that direct staring is avoided and social looking is limited to certain age/social categories: juveniles engage in more looking at other orangutans than do adults or infants. While orangutans use eye movements in social communication, they avoid the more prolonged mutual gaze that is characteristic of humans, and also apparent in chimpanzees and gorillas. Detailed frame-by-frame analysis of videotapes from field and zoo studies of orangutans revealed that they pay visual attention to both human observers and conspecifics by glancing sideways, with the head turned at an angle away from the subject being observed. Mutual gaze was extremely rare, and we have observed only two incidences of gaze following. Orangutans in captivity appear to use a more restricted pattern of gazes compared to free-living, rehabilitating ones, possibly suggesting the presence of a pathological condition (such as depression) in the captive subjects. Our findings have implications for further investigations of social communication and cognition in orangutans.