Does a Social Introduction Alter Cortisol in Captive Bonobos (Pan paniscus)?

For social animals, group living can serve to buffer against stressors. However, changes in the social environment may also represent a stressor leading to changes in glucocorticoids—hormones responsible for maintaining homeostasis under stressful conditions. We studied glucocorticoids in captive bonobos ( Pan paniscus ), a social species of great ape with a complex social organization. We monitored bonobos in captivity before, during, and after a change occurred in their social environment; when a new group member was introduced at the facility. We repeatedly measured individuals' cortisol (corrected for creatinine, or variation in the concentration of samples) from urine samples and found individuals of the established group did not change in cortisol during or following their introduction to a novel bonobo individual. The emigrating bonobo, however, had elevated cortisol upon arrival which decreased as she was introduced to each existing bonobo at the facility. These results suggested that the new individual may have experienced stronger stressors relative to resident individuals during this captive introduction. We recommend based on the results from this study, that social animals be introduced to new group members carefully, and to avoid prolonged social isolation for new animals. When changes in social dynamics are driven by human caretakers rather than initiated by the animals themselves, care should be taken to mimic natural dispersal patterns when possible.