NO. 5 BEHAVIOR OF THE NIGHT MONKEY — MOYNIHAN 



31 



The captive Night Monkeys on Barro Colorado Island and at Iqui- 

 tos usually uttered loud Screams when caught and handled by a 

 human being. (I presume that all Night Monkeys are capable of 

 uttering similar or identical sounds ; but none of the other individuals 

 studied was caught and handled.) These Screams were always high 

 pitched but wavering. Many of them were quite prolonged. Figures 

 5 and 6 are sketches of sound spectrograms of two typical Screams. 



6.000- 



3.600- 



2.400 - 



t.200- 



Fig. 5. — A relatively short Scream, uttered by an adult. 



Based upon a spectrogram by a "Vibralyzer." 

 Only the first harmonic is shown. There certainly was at least one other 

 present. 



All the observed Night Monkey Screams were uttered with the 

 mouth wide open, but they were not accompanied by any conspicuous 

 inflation of the throat region. 



All the captive animals struggled violently when first picked up. 

 Most of the struggling movements were obviously attempts to escape ; 

 but many of the animals also tried to bite their captors whenever 

 possible. The animals usually uttered many Screams during the initial 

 struggles, when both their escape movements and attempts to bite were 

 most vigorous. If the animals were held firmly for several minutes, 

 however, they usually calmed down, gradually, and their struggles sub- 

 sided. At this stage, they generally stopped Screaming and started to 

 utter Gruff Grunts and/or Gulps. 



