Local competitive environment and male condition influence within-bout calling patterns in túngara frogs

Flexible signalling behaviour is widespread, with adjustments often enhancing gains or reducing costs of signalling based on the current state of the signaller’s local communication network. Male túngara frogs call within multispecies communication networks containing conspecifics (both target receivers and rivals) and eavesdropping predators. These diverse players all exert an influence on male calling strategies. We investigated the degree to which patterns of changes in call characteristics across individual túngara frog calling bouts were influenced by callers’ social environment, body condition, and ambient temperature. Most call bouts exhibited two distinct phases, an initial steep increase in call amplitude (the rise) followed by a longer period of more gradual amplitude increase (the plateau). Rises were completed more quickly when males called in denser choruses, while call amplitude increases during plateau phases were greater for males in better body condition. Males also produced more complex calls and increased complexity sooner when calling in denser choruses. Our results suggest that the social environment is the main driver of within-bout calling patterns. This could be due to (i) increased call effort required when competing in denser choruses, (ii) dilution effects provided by nearby rivals releasing callers from eavesdropping risk or, likely, (iii) a combination of both.