(£ SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



rated from their parents. All these individuals were at least \\ months 

 old. 



A perfectly content infant, with all its desires satisfied, is silent 

 and motionless (and usually asleep). Sounds and movements are 

 apparently always indications of dissatisfaction. When an infant is 

 slightly dissatisfied, it may begin either movements or sounds first, or 

 both together. (It is my impression that an infant is most likely to 

 move without vocalizing when it "knows" in advance that it can re- 

 move its dissatisfaction by its own efforts.) The first movements may 

 be nothing more than slight readjustments in the position of the limbs 

 or other parts of the body. At higher intensities of dissatisfaction, the 

 infant usually goes straight to whatever individual or object it ex- 

 pects will be able to satisfy its need {^e.g., a food dish when it is 

 hungry) or, if this is not possible, makes vigorous searching move- 

 ments. 



The hand-reared infants apparently never moved about just for the 

 sake of moving. They did not seem to have any trace of the independ- 

 ent locomotory tendency of adults. All their movements appeared to 

 have an immediate "practical" end in view apart from the mere per- 

 formance of the movements. 



By far the most common vocal patterns of infant and young juve- 

 nile Night Monkeys are Squeaks and Squeaklike notes. A typical 

 "pure" Squeak is brief, not very loud, and much higher in pitch than 

 any of the Grunt Complex patterns. Sketches of sound spectrograms 

 of pure Squeaks are shown in figures 15, 17, and 18. Each pattern of 

 this type sounds like a single note to human ears. The sound spectro- 

 grams, however, indicate that at least many of the pure Squeaks are 

 actually partly or wholly compound, composed of two or three sounds 

 separated by very short intervals or two or three partly distinct 

 "syllables." It will be convenient to refer to such patterns in terms 

 similar to those applied to the equally compound Hoots described 

 above. A pattern that sounded to me like a single note will be called 

 "a Squeak" or "a note." The various sounds which spectrograms 

 may show to be included in a single Squeak, in this sense, will be 

 called "components of a Squeak." 



All the accompanying sketches of vocal patterns by an immature 

 individual are based upon recordings of a single male who was exactly 

 45 days old at the time of recording. 



The pitch of a single Squeak seldom or never remains level through- 

 out. In most cases, the pitch first rises and then falls. When a Squeak 

 is composed of two more or less distinct components, the rise usu- 

 ally extends throughout the first component and the fall throughout 



