Graded or discrete? A quantitative analysis of Campbell's monkey alarm calls

► Primate vocal behaviour is often described as either discrete or graded. ► We experimentally studied the ostensibly discrete Campbell's monkey alarm calls. ► We found that males' alarm calls displayed both graded and discrete features. ► Alarm calls to nonurgent situations were more graded than calls to urgent situations. ► Classifying a species' calls as discrete or graded thus has little heuristic value.