Acoustic Analysis of the Advertisement Calls of the Music Frog, Babina daunchina

The acoustic structure of 18 male advertisement calls of the "music frog" (Babina daunchina), indigenous to the Emei mountain area of Sichuan province in southwest China was analyzed. Previous results showed that Babina typically call from within hidden burrows made by the males and must rely strongly on acoustic information for mate choice. Functioning ecologically as nests, burrows are used for mating, egg-laying, and pre- and postembryonic development. Male Babina calls are spectrally and temporally complex consisting of a sequence of 3-8 notes. Each note consists of a stack of frequency bands, which are nearly integer multiples of the fundamental residue. For all calls the fundamental frequency of successive notes increases monotonically. Moreover, there is a negative correlation between the lowest harmonic (F0) value of the first call note and the increments in fundamental frequency between notes in the same call, implying that constraints exist in the production mechanism. Hierarchical cluster and multidimensional scaling analysis of 29 temporal and spectral call parameters indicate that most of the variance between calls and between males is accounted for by three clusters of call features. The first includes 19 tightly correlated temporal and modulation features including note durations and modulation patterns and total call duration. The second cluster includes the successively increasing fundamental frequencies of the call notes and may reflect that individual males can alter fundamental frequency from call to call. The third cluster includes the dominant frequency bands in calls and may reflect the filter properties of each male's burrow.