Early Trauma Leaves No Social Signature in Sanctuary-Housed Chimpanzees (Pan troglodytes)

SIMPLE SUMMARY: Negative experiences in early life, such as the loss of the mother, can have negative and long-lasting consequences on social functioning in adolescence and adulthood in both humans and other socially living animals, such as our close relative the chimpanzee. Recent studies indicate that zoo-housed chimpanzees may be socially scarred for life after such early trauma in terms of whom they like to be near (social proximity) and whom they entrust keeping their body clean (grooming). In light of these findings, the current study investigated whether the same effect would be identified among orphaned chimpanzees living in social groups in large, forested enclosures in an African sanctuary. Overall, the orphaned chimpanzees were found to be socially indistinguishable from their counterparts who did not lose their mother and were born and mother-reared in the sanctuary. These results suggest that sanctuaries can be valuable rehabilitation centres for orphaned chimpanzees, facilitating chimpanzees’ potential to cope with early life adversities. ABSTRACT: Negative early experiences can have detrimental effects on social functioning in later life, both in humans as well as in other socially-living animals. In zoo-housed chimpanzees, recent evidence suggests that there may be a lingering signature of early trauma on individuals’ social interaction tendencies as measured by social proximity and grooming. Here, we address whether a similar effect would be observable in chimpanzees living under semi-wild conditions in an African sanctuary. By analysing party size, close proximity and social grooming, we show that in this specific sanctuary, chimpanzees that suffered early trauma (n = 42) were socially indistinguishable from chimpanzees who were born and raised by their mothers in the sanctuary (n = 36). Our findings indicate that chimpanzees may not be irreversibly affected by early social trauma, possibly owing to rehabilitation in stable social groups in a semi-natural environment. Beyond identifying sanctuaries as valuable rehabilitation centres for orphaned chimpanzees, this study demonstrates a remarkable social flexibility in one of our closest living relatives.