Each segment (formerly “note") in the mating call of the treefrog Hyla arborea savignyi has two main concentrated bands of energy in the low part of the frequency spectrum and often another one in the upper part. In each segment fall time greatly exceeds rise time. During calling, males change some segment characteristics: dominant frequencies I, II and III become higher; segment duration and fall time become longer; rise time and the interval between segments become shorter. The changing of acoustic characteristics in the course of the mating call is probably a distinct feature of the calling behaviour of H. a. savignyi males that (like pausing between calls) might conceivably serve to avoid monotony.
Little research has been done on the intraspecific aspects of vocal behaviour of anurans. The purpose of this study was to examine the possibility that there are individual call characteristics within a population of the treefrog Hyla arborea savignyi. Ten individuals from two close localities near Jerusalem, Israel were recorded in the laboratory. Individuals differed significantly from each other in one or more of the parameters tested (three dominant frequencies, segment duration, rise time, fall time, intersegmental interval, call duration and segment repetition rate) and in absolute values of the frequency spectrum. They do not differ significantly in the distribution of energy in the spectrum (the shape of the spectrum). The range of the percentage of pairs within which differences in a particular parameter were found was 31-67%. The most common individual characteristics were fall time, segment duration and dominant frequencies I, III. Individuals differ also in the exact form of changes that occur in call parameters during the call. The individual differences were not a result of different recording temperatures, nor of differences in body size. The results show which (if any) call characteristics or their combination could be used for individual recognition; they do not imply that such recognition actually takes place in this species.