Introduction

Many mammals give long-range calls that can be received over wide areas, often containing large numbers of receivers. In the case of mammals with fluid social systems, opportunities for exposure to the calls of others are further enhanced by the movement of individuals with respect to one another. In our chapter, we discuss the relevance of eavesdropping and communication networks in a range of mammal species, first considering how these concepts apply in cases where loud calls are used to exchange social information in static territorial and fluid fission–fusion societies, and then exploring their potential importance where mammals use loud sexual calls to broadcast information about resource-holding potential. We also outline the mechanisms by which information in mammalian calls is encoded, broadcast and acquired, and we consider the possible fitness consequences that attending to calling interactions can confer. Finally, we evaluate how the vocal communication networks described for non-human mammals differ from human communication networks and discuss possible explanations for these differences.

When mammals give loud calls, the area over which the signal can be received is potentially extensive. Such calls are typically emitted at high sound-pressure levels (greater than 100 dB at 1 m) and while spherical spreading and excess attenuation from the environment eventually result in the signal being engulfed in background noise, it often remains intelligible over distances of several kilometres from the source: for example the calls of lions Panthera leo (Ogutu & Dublin, 1998; Funston, 1999; K. McComb, unpublished data), hyaenas Crocuta crocuta (Ogutu & Dublin, 1998) and elephants Loxodonta africana (McComb et al., 2003).