After the fight: post-contest acoustic signalling

Animal contests often involve acoustic signals at different stages, but empirical work has primarily focused on usage before and during antagonistic interactions. Far less attention has been paid to post-contest acoustic signals (PCAS): those occurring after the outcome is decided. We begin by describing three main functions of PCAS—showcasing winning, minimising costs of losing and repairing/affirming relationships—illustrating our ideas with taxonomically diverse examples involving resource defence and within-group social conflict. We also highlight additional contexts where PCAS are likely produced and how to test between different functions, providing specific predictions about acoustic characteristics, signaller behaviours and receiver responses. We then focus on the two signalling parties. First, we discuss environmental, social and contest factors that might drive interspecific and intraspecific variation in signaller production of PCAS. Second, we consider the varied types of information within PCAS, how their value can decay or accumulate, and how that affects their importance and reliability to receivers over different timeframes. We finish by suggesting future studies to expand our understanding of PCAS and how this, and manipulating PCAS, can provide deeper knowledge not just about contest consequences but also animal conflict, information use, communication, social interactions, behavioural flexibility and cognition more generally.