Usage of song repertoire and male-male communication in pale-legged leaf-warbler

In many songbird species, an individual bird sings multiple song types, i.e., has a song repertoire. Song repertoires are used in territorial defense and mate attraction. However, there is no substantial evidence that conspecific individuals attend to the number of different songs that a male can sing. I studied the pale-legged leaf-warbler Phylloscopus tenellipes, a species with a repertoire of up to 11 song types. I simulated territorial intrusion by broadcasting conspecific songs in territories. While singing spontaneously, males usually used only one song type repeated continuously (S-singing mode). They typically responded to playback by switching from a single song type to multiple (up to 8) song types sung with immediate variety (V-singing mode). The same song type can be used by a male in both singing modes. Then, I tested each male with a different pair of contrasting stimuli, consisting of either a single song type or five song types. Males responded differentially depending on the singing mode as multiple song stimuli elicited a stronger response. Therefore, both signaler and receiver behavior are consistent with a role of song-type diversity and switching rate but not song structure per se in male-male communication.