The songs and calls of birds of course advertise the singer’s species and often its sex. But some might be surprised to learn that subtle variants of a bird’s vocalizations can reveal other highly relevant information to receivers, such as its age, health, aggressiveness, and quality as a mate. Birds can even engage in reciprocal negotiations via these variants. An underlying issue of great theoretical importance to animal communication researchers is how such signals remain honest in competitive contexts, where signalers might benefit if they exaggerated or bluffed. In this lecture I will review a few studies colleagues and I have undertaken to examine the signaling function of such song variants and the likely factors that keep them honest most of the time.