Countersinging in territorial birds has been viewed as a form of vocal contest. We studied the role of song repertoires in countersinging by western meadowlarks, Sturnella neglecta, by simultaneous observations of neighboring males. Neighbors tended to switch song types synchronously, but tendency to lead or follow in such switches did not correlate with orientation, subsequent behaviour, tendency to interact (as measured by the number of repetitions of each song type), or breeding stage. Males did not match song types, but were more likely to sing if their neighbour sang a song type that they shared. We suggest that synchronous switching is not a vocal contest in this species, but may be a form of competitive advertisement.