NO. 5 BEHAVIOR OF THE NIGHT MONKEY — MOYNIHAN 79 



Hill (1960) summarizes several accounts by earlier observers and 

 quotes some of their transcriptions of vocal patterns. The notes 

 variously transcribed as "oo-oo-oo," "bu-bu-bu," and "boom" may be 

 the same as the notes I have called Hoots. The notes transcribed as 

 "chip-chip-chip," "chuip-chuip," and "kweep-kweep" presumably are 

 Squeaks. The notes transcribed as "urr-urr" may be Gruff Grunts. 



Sanderson {op. cit.) says that a Night Monkey that he kept in 

 captivity uttered "grrrrrrmph" notes as a sign of contentment or 

 pleasure. His transcription would suggest that the notes were Grunts ; 

 but, if so, his interpretation of their significance is almost certainly 

 wrong. He may have been misled by the fact that captive Night 

 Monkeys sometimes utter many Gruff Grunts without extreme or im- 

 mediately recognizable attack and escape movements, after they have 

 learned that such movements do not produce the desired results, i.e., 

 after they have learned that they cannot get out of their cages or force 

 their captors to retreat permanently. 



Sanderson mentions a variety of other sounds, all or most of which 

 are unidentifiable. He also says that no two individual Night Monkeys 

 have the same repertory of sounds. This is not only extremely im- 

 probable per se, but is not borne out by my own observations. All 

 Panamanian Night Monkeys probably utter almost exactly the same 

 types of sounds, although there may be slight differences (in pitch, 

 length, or loudness) between the equivalent sounds of different indi- 

 viduals, and different individuals may utter the same sounds in slightly 

 different situations, presumably because they have had different 

 histories. (All the more or less distinctive notes and calls which were 

 heard uttered by only one individual were extremely rare; and it 

 seems likely that further observations would have shown that they are 

 also present in the repertories of other individuals.) 



The most extensive pubHshed descriptions of Night Monkey calls 

 are by Andrew {op. cit.). His account is based upon observations of 

 two individuals in the laboratory. Unfortunately, he does not say 

 where his animals came from or describe the conditions in which they 

 were kept. As a result, it is difficult to interpret some of his findings. 



All or most of the patterns that he calls "twitters" would seem to be 

 varieties of what I have called Squeaks. So, in all probability, are 

 the notes that he calls "guinea-pig squeaks." (It may be worth men- 

 tioning that none of the Squeaks or Squeaklike notes of the individuals 

 kept on Barro Colorado appeared to have "traces of clicks" like those 

 which Andrew describes as being superimposed upon twitters.) The 

 patterns which Andrew calls "trills" may be "High Trills" according 



