For many taxa, vocal communication is an essential means of navigating continuously changing social and ecological environments. Among passerine birds, vocal signals are critical to survival and play an important role in mate attraction, territory defense, and predator avoidance. In my dissertation, I study acoustic communication in a wild population of blue tits and great tits in order to investigate the effects of social environment on birds’ responses to acoustic cues as well as their production of acoustic signals. In Chapter 1, I demonstrate that blue tits can learn to associate a novel acoustic cue with predation risk, and that the behavioral response to this cue can be socially transmitted to naïve great tits, despite their lack of first-hand experience. This study suggests that social learning of acoustic cues can occur between species. In the second chapter, I develop an unsupervised machine learning approach that can objectively measure similarity of vocal signals. I present this technique such that it can be broadly applied for the analysis of diverse acoustic datasets. Using this approach, I then explore patterns of variation in great tit songs from multiple angles. In Chapter 3, I develop and test a mathematical model that describes the optimal levels of vocal similarity among neighbors under given social and ecological conditions. This model predicts that immigrant and resident birds will exhibit comparable levels of vocal similarity with neighbors, despite having different song learning opportunities in their natal environments. My empirical results agree with model predictions, showing that although immigrants more often use complex, unshared songs, they achieve high levels of vocal similarity with neighbors by using larger repertoires than residents. I further explore spatial and temporal variation of great tit songs in Chapter 4, and show that an individual’s songs reflect both their immigration status and their breeding territory location. I also find that songs change between subsequent years, and that this is largely due to the appearance and disappearance of individual birds. Together, my findings suggest that individuals continuously adapt their vocal behavior to changing social environments, and that interactions with both conspecifics and heterospecifics may shape vocal communication systems.