NO. 5 BEHAVIOR OF THE NIGHT MONKEY — MOYNIHAN 69 



of the slight (inaudible to human ears) division into separate com- 

 ponents M^hich is characteristic of many Squeaks. Figure 17 includes 

 a pattern of this type. The intergradation between pure Squeaks and 

 pure Screams seems to be complete, insofar as infants and young 

 juveniles utter every possible type of morphologically intermediate 

 pattern. 



3,600- 

 1.200- 





^s 



-^ , P~ — .. .^ -, 



0.2 0.4 



Fig. 17. — A "pure" Squeak, followed by a longer note more or less perfectly 

 intermediate between a Squeak and a short Scream. Uttered by an immature. 



Based upon a spectrogram by a "Vibralyzer." 

 Compare with the Scream shown in figure 5 and the Trills shown in figure 19. 



"Pure" High Trills are conspicuously compound. To human ears, 

 each High Trill sounds as if it were composed of three or four 

 Squeaks uttered in rapid succession. Most sound spectrograms convey 

 the same impression. A sketch of a more or less typical pure High 

 Trill is shown in figure 18. The successive notes in a single High 

 Trill are seldom exactly the same pitch. In most cases, the first one 

 or two notes are largely or completely rising and the last one or two 

 notes are largely or completely falling. 



A remarkable feature of the vocal repertory of young Night Mon- 

 keys is that the arrangement of components within a single Squeak, 

 i.e., the sequence of changes in pitch and the relative distance be- 

 tween high points and low points is sometimes similar to the arrange- 

 ment of successive Squeaks within a single High Trill. Thus, the 



