Introduction

Communication in networks has received considerable research attention over the last few years (Naguib & Todt, 1997; Otter et al., 1999; Peake et al., 2001; Mennill et al., 2002; Ch. 1). This is true for two types of network interaction, one in which several receivers react to the signal of just one individual and a more complex one in which receivers eavesdrop on the signal exchange of two or more individuals and use the information they gained in their own decision making (McGregor & Dabelsteen, 1996; Ch. 2). If we think about communication, the fact that there often is more than just one individual receiving any given signal is not surprising. One reason that many studies on more transient signals concentrated on only one signaller and one receiver was a methodological problem. It is notoriously difficult to sample behaviour from more than one or two individuals at a time, especially if interactions are rapid and involve movements of individuals. Recently, the simultaneous tracking of several individuals in a large group has become feasible. This has led to an increase in studies investigating the effects of signals on several receivers in rapid communication interactions. Many such studies have concentrated on the acoustic domain, a modality that is inherently transient. Signals rarely last more than a few seconds and usually provide a variety of different messages within a single signal.

While there is ample evidence from terrestrial environments that more than one individual can receive and use information from a call or a calling interaction, data on acoustic communication networks in marine environments are sparse.