AbstractBirdsong overlapping may either indicate communicative interaction between birds or be a simple coincidence. We developed a program that allowed us to mathematically modulate the independent singing of birds with a given level of song rate. This permitted us to statistically evaluate whether song overlapping is a random coincidence or real acoustic interactions between birds. Analysis of automatic recording (Song Meter SM4) of singing detected the cases of reliable acoustic interactions between both conspecific and heterospecific individuals. They account for 6% of the total singing time. The most numerous and actively singing chaffinches (in the case of singing of several individuals) suppress the singing of other species. The singing of a single chaffinch, on the other hand, can provoke the singing of other species, involving previously silent neighbors in song duels. It is possible that it is the acoustic interactions that are responsible for maintaining the structure of the population at the end of the breeding season.