The influence of sex, rearing history, and personality on abnormal behaviour in zoo-housed bonobos (Pan paniscus)

Abnormal behaviours are often used as a welfare indicator in zoo-housed great apes. While previous studies report on the occurrence of abnormal behaviours in zoo-housed chimpanzees (Pan troglodytes), there is currently a lack of knowledge about such behaviours in the closely related bonobo (Pan paniscus). Here we report on the prevalence, diversity and frequency of abnormal behaviours, based on 1531 h of observations in 51 adult bonobos, living in six zoos. We also investigate the potential influence of age, sex, rearing history and four previously established personality traits (Activity, Boldness, Openness and Sociability) on the diversity and frequency of abnormal behaviours. Our results document the presence of a total of 13 abnormal behaviours in the population, with the five most frequent ones being Coprophagy, Poke anus, Social hair pluck, Regurgitation and Head shake. We find that wild-born bonobos show a higher diversity of abnormal behaviours compared to mother-reared individuals, likely due to their abnormal early-life experiences. Mother-reared individuals and males show lower frequencies of Poke anus. The frequency of abnormal behaviours is also linked to personality. Bonobos scoring lower on Activity, associated with more self-scratching and lower activity, engage more in Coprophagy and Head shaking. More sociable individuals, on the other hand, had higher frequencies of Social hair pluck, which follows a previous finding that this behaviour is embedded in grooming. Finally, more sociable individuals also had lower frequencies of Coprophagy, an indicator that higher sociability might cause higher resilience to stressors. Our study provides a first overview of the abnormal behaviours in zoo-housed bonobos. We discuss that not all abnormal behaviours may be suitable indicators of poor welfare. These results form an important base in our understanding of the repertoire of abnormal behaviours in zoo-housed bonobos, which is a crucial step for optimising their welfare.