The question of how animals adapt their signals and behaviors to variable physical and social environments is central to the field of behavioral ecology. Throughout an animal's lifetime, both the social context they experience and their own characteristics can change. Much is known about the mechanism, function and evolutionary origin of reproductive strategies across taxa, especially tactics that are fixed over time. Much less in known about plasticity in mating and signaling strategies within an individual's lifetime. Here, we investigate how male mating and signaling strategies vary with attractiveness in a promiscuous, duetting bird species, the Red-backed Fairy-wren. We conducted behavioral observations and experimental tests to determine: 1. the function of vocal duets, 2. how signal function and general mating strategy vary with male attractiveness and 3. whether these mating and signaling strategies are effective and yield fitness returns. We found that male birds use duets to mediate both territorial and breeding interactions. The degree to which males use duets for acoustic mate guarding (i.e. duetting to repel rivals and protect paternity), and whether the employ other physical mate guarding tactics, depends on the social environment each male experiences. Unattractive males (those who are not preferred by females and have little success obtaining extra-pair matings) used duets for acoustic mate guarding and invested in intense physical guarding of mates. Attractive males used duets primarily for territory defense and invested most in obtaining additional matings. Both physical and acoustic guarding were effective, since they prevented intrusions from rival males, but acoustic guarding repelled rivals to a lesser degree. Each male's strategy appeared to provide him optimal reproductive success. Specifically, unattractive males had higher within-pair reproductive success, attractive males higher extra-pair reproductive success, resulting in equal total reproductive success between male types. Our research fills an important gap in our understanding of how flexible mating strategies can evolve, since there appears to be selection for males to adjust the mating strategy they use continually, depending on the mating opportunities available to them. Our studies also show that duet function can vary, depending on the signaler and his social priorities.