Frequency modulation seems apparent, occurring in this case from pulse to pulse 

 within each quack. In all quacks the average maximum energy expenditure seems 

 to be at around 1500 Hz. In most cases, however, with each succeeding pulse 

 within a quack, the dominant frequency increases somewhat. This is easily seen 

 in the contour displays where, although individual pulses cannot be distin- 

 guished, the axis of the amplitude contours for each succeeding quack becomes 

 increasingly inclined upward to the right. In the last several quacks there 

 are a relatively large number of pulses per quack involved. This increase in 

 pitch from start to finish of a quack is quite evident to the listener. Again, 

 as in the case of the Longspine Squirrelfish quacks, it would be interesting to 

 isolate individual pulses and recombine them in various manners in order to 

 determine the factors responsible for the quacking quality of the sounds. 



Squeaking Door Sound : 



The Longspine Squirrelfish produces an occasional intense burst of pulses which 

 together sound much like a door being swung slowly on dry hinges. Quite a bit 

 of variability in temporal spacing of the pulses is evident, and intervals as 

 short as .01 sec. and as great as .26 sec. appear in Figure 8B„ A pair of 

 double pops precedes the major sound sequence in this and other squeaking door 

 s o und s examined . 



The frequency distribution is broad within most of the pulses but a slight 

 bimodality is demonstrable. Slightly greater energy expenditures are distrib- 

 uted around 900 Hz and 1500 Hz. There is, however, a fair amount of frequency 

 modulation associated with this sound, and in actuality it is composed of four 

 distinct types of pulses including the bimodal one described above. 



The last 5 pulses of the series represented in Figures 8B and 9A are of two 

 types. One, represented by the last pulse and the third and fifth from last, 

 is dominated by frequencies centering at about 1250 Hz, with slight additional 

 modal tendencies at 800 Hz and 300 Hz. The second and fourth from the last 

 pulse and also the 12th pulse from the beginning of this sequence demonstrate 

 maximinn amplitude at a relatively high frequency, 2100 Hz, without appreciable 

 low frequency components . 



Near the center of the sonogram is a short purr-like sequence of four pulses 

 dominant around the 900 Hz level without any apparent second mode at higher 

 frequencies . 



Although it would seem that innumerable combinations of the four types of 

 pulses described above are possible, the significance of such combinations in 

 transmitting information is as yet poorly understood. 



Roar: 



This is another jound of unknown origin. It consists of a series of thumps and 

 pulses of variable amplitude and temporal spacing (Figure 9B) . The thumps are 

 composed of from 2 to 3 individual pulses and are spaced from .04 sec. to .15 

 sec. apart. They initiate the sequence and give way after .6 sec. to a series 

 of closely spaced pulses and thumps of greater amplitude. Whereas the prelimi- 

 nary thumps rise 24 decibels above the quietest background in the 100 to 400 Hz 

 range, the more intense roaring segment of this sound attains this level at 



VI-96 



