NO. 5 BEHAVIOR OF THE NIGHT MONKEY — MOYNIHAN 7I 



interpreted as continuous series of either Squeaks or components of 

 Squeaks. (These relationships are difficult to describe or explain 

 verbally, but I think that they will become clear if the accompanying 

 drawings of sound spectrograms are studied in detail.) 



In view of these facts, it is not surprising that the patterns inter- 

 mediate between pure Squeaks and pure High Trills appear to be 

 somewhat heterogeneous. Some intermediates are moderately rapid 

 series of a few obviously distinct notes, apparently series of Squeaks 

 which are not accelerated as much as the components of pure High 

 Trills. Others are brief patterns which sound rather like single 

 Squeaks with faint "rattling undertones." These may be Squeaks in 

 which the internal components have become more distinct from one 

 another than in typical pure Squeaks. The two intermediate types 

 intergrade with one another. It is my impression, in fact, that the 

 intergradation between pure Squeaks and pure High Trills is as 

 complete as the intergradation between Squeaks and Screams. 



Infant and juvenile Night Monkeys also utter many patterns that 

 seem to be intermediate between Screams and High Trills. These 

 are all more or less prolonged, discontinuous, and wavering. Figure 

 19 is a sketch of two patterns of this type (somewhat nearer to pure 

 High Trills than to pure Screams). At least equally common are 

 patterns that appear to be intermediate between High Trills, Screams, 

 and Squeaks. These are similar to the intermediates between High 

 Trills and Screams but shorter. 



It is evident, therefore, that the patterns which have been called 

 pure Squeaks, pure Screams, and pure High Trills in the preceding 

 discussion are merely the extreme points of a continuum. This whole 

 group of patterns may be called the "Squeak Complex." 



It seems probable that all the vocal patterns of both adult and young 

 Night Monkeys can be included in either this complex or the Grunt 

 Complex. 



The mouth is opened to a moderate extent during all or most notes 

 of the Squeak Complex (see figure 22). 



Infants raised apart from their natural parents utter Squeaks and 

 intermediate notes closely similar to pure Squeaks very frequently 

 whenever they are not clutching a foster parent or parent substitute 

 (if they are not "distracted" by food or drink). A tame infant which 

 has been silent while being carried by a human being will always begin 

 to utter Squeaks (with or without other notes — see below) as soon 

 as it is lifted away. It may also start to move in an obvious attempt 

 to follow and rejoin the human being. Its Squeaks may become louder 

 and more rapid if the human being then disappears from sight. 



