NO. 5 BEHAVIOR OF THE NIGHT MONKEY — MOYNIHAN 73 



Infant Night Monkey would respond to its Squeaks by trying to make 

 it more comfortable, e.g., by helping it to readjust its position or by 

 feeding it. 



Unfortunately, this could not be checked by observation of the 

 infants raised by their own parents in captivity. The parents of both 

 infants seemed to be attentive and conscientious, and the infants were 

 silent most of the time, presumably because they were seldom suffi- 

 ciently uncomfortable or thwarted in the right way to induce vocaliza- 

 tions. I did hear them utter a few Squeaks, quite like those of the 

 hand-reared infants. They uttered these notes in a variety of circum- 

 stances, e.g., while moving around on a parent's back, while trying to 

 suckle, and (once) after falling off a parent's back. In most cases, 

 the infants stopped vocalizing almost immediately, before the parents 

 reacted. They apparently managed to achieve satisfaction by their 

 own efforts. The infant that fell was retrieved by a parent, but I 

 could not determine if this parental act was a response to the infant's 

 Squeaks and/or to the scrambling movements that it made at the 

 same time. 



The fact that high-pitched notes will not carry as far as low-pitched 

 notes has already been mentioned. It seems highly probable that the 

 Squeaks of infants, like those of adults, are primarily short-range 

 signals. Under natural conditions, they are probably almost always 

 uttered by infants at least fairly close to their parents. 



It is my impression that the Squeaks of both adults and young are 

 slightly "ventriloquial." In the dark, I found it difficult to tell exactly 

 where Squeaks were coming from. Their source was more difficult 

 to locate than that of any other vocal pattern of the species (with 

 the possible exception of some High Trills). 



These features may be particularly advantageous because individ- 

 uals uttering Squeaks may be so intent upon the activity in which 

 they are engaged, or so distressed, that they may become less alert 

 than usual to outside stimuli and fail to note the approach of a pos- 

 sible predator. 



Infants may utter Squeaks (and/or closely related short interme- 

 diate notes) singly or in unaccelerated series {i.e., series that are not 

 at all Trill-like) of up to seven or eight notes. Longer series presum- 

 ably are produced by greater distress than shorter series. Series are 

 frequently repeated with only brief intervening pauses. 



Infants also utter many series of notes which include both brief 

 Squeaks or Squeaklike notes and longer Screams or Screamlike notes. 

 The arrangement of notes in such series is quite variable. One com- 

 mon arrangement is three or four long notes followed immediately 



