||Moving animal hybrid zones have been investigated rarely, and their behavioral dynamics are poorly understood. Black-capped and Carolina chickadees interbreed in a narrow northward-shifting band. Using recordings of vocalizations gathered within and outside their hybrid zone in southeastern Pennsylvania, I analyzed changes in songs and calls between 2000 and 2010, and I investigated behavioral responses to song. In the hybrid zone, Carolina songs have become more common, Black-capped songs less like those in pure populations, and 'chick-a-dee' calls more Carolina-like. Where hybridization is recent, Black-capped song persists, but 35% of calls are Carolina-like. These data suggest that vocal changes in this hybrid zone may not take place until several years after genetic introgression begins. Further, playback experiments show that males that sing both parental song types do not use them in any pattern in territorial interactions. The utility of an expanded repertoire in hybrid chickadees is therefore still not understood.