The little blue penguin, Eudyptua minor, was used to examine three specific issues in animal communication. (1) Ethologists have traditionally viewed social repertoires as being fixed and invariable. In contrast, my analysis of agonistic behaviour of little blue penguins occupying two different habitats revealed significant variation in repertoire size and form. Cave-dwellers, which had large and complex repertoires, occupied open colonies characterized by high interaction rates. Burrow-dwellers, which had small repertoires, occupied colonies in which conspecifics were isolated from one another and rarely interacted. Despite higher interaction rates, cave-dwellers attacked one another less often and used overtly aggressive behaviours with shorter durations than did burrow-dwellers. The results suggest that the size and form of repertoires may be mediated by the social and physical properties of occupied habitats. Large repertoires may reduce the proportion of encounters leading to overt aggression where interaction rates are high. (2) Theoretical models of aggressive communication suggest that animals are unlikely to use aggressive displays to signal motivation. Using lag sequential analysis, I examined over 2000 agonistic interactions between cave-dwelling penguins. The results suggested that aggressive displays differ in how costly they are to perform (i.e. as measured by the risk of escalation) and that high cost displays were more effective in deterring opponents than low cost displays. I argue that animals can signal motivation by taking risks during interactions, as demonstrated by their choice of display. (3) The social facilitation of courtship behaviour is a widely assumed but rarely demonstrated process thought to be related to breeding synchrony. Using a playback experiment, I demonstrated that the acoustic components of penguin displays facilitated courtship behaviour from perceiving conspecifics. I argue that social facilitation may alter the availability of social stimuli and cluster acts of copulation, both of which may influence the timing and synchrony of breeding.