The syntactical organization of the avian song is of particular interest in light of recently discussed analogies between the songs of birds and human speech. We present here a description of the song structure of the Siberian Rubythroat Calliope calliope, a small insectivorous bird, widespread in Siberia and the Russian Far East. This species sings predominantly discontinuously, but the duration of individual songs varies significantly. Each individual song is composed of a number of song units, a stereotypical set of different notes and syllables that are always presented together and in a strictly fixed order. Although the variety of song units in an individual's repertoire is significant, the diversity of units presented in the very beginning of individual songs was found to be much more limited. The song of the Siberian Rubythroat is not only extremely complex and variable, but it is also organized as a set of clusters rooted in strictly defined initial song units. Each cluster in turn contains several branching points with a limited number of branches. Despite its impressive variety, the rubythroat's song nevertheless contains numerous fixed sequences of song units.