RULES OF PARAMETER VARIATION IN HOMOTYPE SERIES OF BIRDSONG CAN INDICATE SOLLWERT SIGNIFICANCE

Various bird species produce songs which include homotype pattern seri es, i.e. segments composed of a number of repeated vocal units. We com pared such units and analyzed the variation of their parameters, espec ially in the time and the frequency domain. In addition, we examined w hether and how serial changes of both the range and the trend of varia tion were related to song constituents following the repetitions. Data evaluation showed that variation of specific serial parameters (e.g., unit pitch or unit duration) occurring in the whistle song-types of n ightingales (Luscinia megarhynchos) were converging towards a distinct terminal value. Although song-types differed in this terminal value, it was found to play the role of a key cue ('sollwert'). The continuat ion of a song depended on a preceding attainment of its specific 'soll wert'. Our results suggest that the study of signal parameters and rul es of their variations make a useful tool for the behavioral access to the properties of the control systems mediating serial signal perform ances.