In mammals, vocal signals are produced in many social contexts and convey diverse information about the emitter (social rank, individual identity, body size-condition). To understand their biological function, the authors find it is not only important to estimate the information about the signaler encoded in the signal but also to determine if and how this information is perceived by the receiver. In male pinnipeds (phocids, otariids, and odobenids) vocal signaling plays an important role in the breeding season during the defense of territories, females, or both. In this article, the authors investigated 2 key acoustic features that Australian sea lion (Neophoca cinerea) males most likely rely on to assess the threat level posed by potential rivals, by manipulating bark rhythmicity and spectral characteristics. Bark series that show accelerated rhythmicity and higher formants elicited stronger responses.