44 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



Cehiis, and Ateles. In these latter species, all or most of the major 

 adult vocal patterns seem to intergrade with one another through 

 nearly continuous series of common intermediate notes. 



Such differences in organization of the vocal repertory presumably 

 are correlated with different ways of functioning. 



When an adult of a Cehus species is motivated by three or four 

 different tendencies {e.g., attack, escape, sex, and gregariousness), 

 it may be able to express all the tendencies simultaneously by uttering 

 a single ambivalent vocal pattern, more or less perfectly intermediate 

 between the patterns which would be produced by each one of the 

 tendencies (or pair of tendencies) if activated alone. A signal of this 

 type must contain a relatively large amount of information. This in 

 itself must be advantageous. But such signals may have disadvan- 

 tages as well. It may be difficult for the receiver of a signal of this 

 type to perceive or "decipher" all the information contained in the 

 signal. Complex signals are probably more easy to misunderstand 

 than simple signals containing less information. In these adult monkey 

 repertories, it is also probable that the frequency of intermediate notes 

 reduces the contrast between different signals. These features may 

 induce momentary confusion in the individual (s) toward which 

 the signals are directed. Even when confusion is avoided, they must 

 tend to reduce the speed of the response to the signals. This is prob- 

 ably very disadvantageous. There is evidence that selection always or 

 nearly always tends to favor increased rapidity of social responses 

 (Moynihan, 1963b). 



An adult Night Monkey motivated by a complex combination of 

 tendencies usually does not utter intermediate notes, but rather a 

 series of different types of notes, each one of which expresses only 

 one or two of the tendencies. Thus, for instance, a wild adult sur- 

 prised by a disturbing stimulus may utter a rapid "jumble" of Gruff 

 Grunts, Moans, Gulps, Low Trills, and Sneeze-grunts, not b. single 

 vocal pattern expressing the complete combination of attack, escape, 

 locomotory, and (possibly) other tendencies by which it is motivated. 

 This sort of message may be able to convey as much information as 

 a single note expressing all the tendencies simultaneously, if the ar- 

 rangement of the different notes is not random and if the receiver's 

 reaction to the first note does not interfere with its reactions to the 

 later notes ; but it is certainly produced with greater physical effort 

 and, more important, more slowly. The principal advantage of this 

 sort of message presumably is that each one of its constituent notes, 

 being an expression of only one or two tendencies, is a comparatively 

 simple signal and, therefore, difficult to misunderstand. 



