The ability of animals to adapt to context is one of the most important challenges facing any individual. This is particularly important when it comes to sexual signalling and courtship, when the choice to signal or not signal may determine whether or not a given animal gets to live–or whether it gets to reproduce. Signals often impose costs on individuals, including energetic, predatory, and social costs, and individuals must integrate the cost/benefit analysis of signaling before making the decision to signal or remain hidden. Leptin is an exciting potential overall signal for male animals to self-monitor because it responds to many contexual cues about body state, including energetics, immune challenge, and sleep. Here we explore the effect of leptin manipulations on investment in male advertisement song on neotropical singing mice. We administered intraperitoneal injections of mouse leptin (Mus) to male singing mice immediately before a playback protocol designed to evoke song, a social advertisement behavior. Mice injected with leptin sing back more frequently than mice injected with saline, and they have a shorter average latency to respond to playback than saline-injected mice. Interestingly, we find that these results appear regardless of fasting state prior to testing: all animals in this experiment were fed ad libitum, suggesting that variations in endogenous leptin are monitored by individuals even when leptin levels are too high to significantly alter feeding behavior.