Male competition strategies change when information concerning female receptivity is available

Males compete for access to resources or females or to influence female mate choice in many animal species. Male competitive activities are accompanied by high-energy expenditure and increased risk of predator detection. We therefore hypothesized that information predicting female receptivity could affect male competition strategies in species in which such information is available to males. To test this hypothesis, male–male vocal competition was assessed in Xenopus laevis, a species in which females can produce receptive (rapping) and unreceptive (ticking) calls. Male vocalizations were recorded when 1) males called alone, 2) 2 paired males with similar body mass called competitively and established dominance, and 3) the paired males called when listening to playbacks of either rapping or ticking calls. On average, rapping but not ticking playbacks increased male calling and in many cases induced previously nondominant males to call more than their rivals. Moreover, males adopted either of 2 competitive strategies: an assertive strategy in which some individuals always called at a high rate and an opportunistic strategy in which some individuals only called at a high rate in the presence of receptive female call playbacks. Body mass and call rate were correlated only when males called alone or when rapping calls were played back. These results support the idea that male–male competition strategies can be influenced by information indicating that receptive females are present.