Acoustic generators 3 Complex sounds 3 Delay differential equations 3 Differential equations 3 Sound source 3 Bird species 2 Birds 2 Complex solution 2 Mathematical models 2 Motor commands 2 Oscillatory solutions 2 Parameter spaces 2 Periodic solution 2 Sound production 2 Vocal-tracts 2 Acoustic effects 1 Acoustic features 1 Acoustic interaction 1 Acoustic signature 1 Acoustics 1 Behavioral research 1 Bioacoustics 1 Biomechanics 1 Close-in 1 Complex behavior 1 Coupled systems 1 Fundamental frequencies 1 Hysteresis phenomenon 1 Ideal model 1 Limit cycle 1