The well-known "roar/shriek chorus" is spontaneous, occurring most often during period of high activity, as well as being contagious, involving communal participation including infants three to four months old. "Abrupt roars" are also more common during high activity and aside from alerting group members to the presence of an avian predator, they probably also help maintain contact with individuals outside of visual range or indicate an aggressive/defensive response to a disturbance. In the wild, both of these calls are emitted more during the hot, rainy season due to heighten activity. All high-amplitude calls are delivered with from a "taut" body posture.