CHARACTERIZING THE GRADED STRUCTURE OF FALSE KILLER WHALE (PSEUDORCA CRASSIDENS) VOCALIZATIONS

The vocalizations from two, captive false killer whales (Pseudorca cra ssidens) were analyzed. The structure of the vocalizations was best mo deled as lying along a continuum with trains of discrete, exponentiall y damped sinusoidal pulses at one end and continuous sinusoidal signal s at the other end.;Pulse trains were graded as a function of the inte rval between pulses where the minimum interval between pulses could be zero milliseconds. The transition from a pulse train with no inter-pu lse interval to a whistle could be modeled by gradations in the degree of damping. There were many examples of vocalizations that were gradu ally modulated from pulse trains to whistles. There were also vocaliza tions that showed rapid shifts in signal type-for example, switching i mmediately from a whistle to a pulse train. These data have implicatio ns when considering both the possible function(s) of the vocalizations and the potential sound production mechanism(s). A short-time duty cy cle measure was developed to characterize the graded structure of the vocalizations. A random sample of 500 vocalizations was characterized by combining the duty cycle measure with peak frequency measurements. The analysis method proved to be an effective metric for describing th e graded structure of false killer whale vocalizations. (C) 1998 Acous tical Society of America. [S0001-4966(98)03609-1]