A Possible Population-Driven Phase Transition in Cicada Chorus

We investigate the collective synchronization of cicada chirping. Using both experimental and phenomeno- logical numerical techniques, here we show that the onset of a periodic two-state acoustic synchronous behavior in cicada chorus depends on a critical size of population Nc = 21, above which a typical chorus state appears periodically with a 30second-silence state in between, and further clarify its possibility concerning a new class of phase transition, which is unusually driven by population. This work has relevance to acoustic synchronization and to general physics of phase transition.