50 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



which it was possible to make spectrograms. They seem to have been 

 somewhat different from the Hoots of a young male sketched in figure 

 20. I think that the differences between the Hoots of these two in- 

 dividuals were due to the difference in their age, not their sex.) 



The adult Night Monkeys on Barro Colorado Island uttered Hoots 

 singly and in short series of two, three, and four notes. Two was the 

 most common number. The Iquitos animal apparently always uttered 

 Hoots in series of three or four. 



The postures and movements accompanying Hoots were observed 

 only in captive individuals. The Barro Colorado adults uttered their 

 Hoots while sitting in a perfectly normal unritualized posture, hind 



0.2 0.4 0.6 0.8 l-O 1.2 '••♦ '•<> '■* 



Fig. 13. — Three Hoots, uttered by an adult female. 



Based upon a spectrogram by a "Sona-graph." 

 The harmonics accompanying these notes are not shown. 



limbs flexed, back slightly curved (as in all sitting postures), and 

 hands firmly grasping the perch. They usually looked more or less 

 straight forward throughout their performances. The mouth was 

 opened slightly as each Hoot was uttered, and apparently closed be- 

 tween the successive notes of a series. The throat and upper breast 

 were inflated with each note, and subsided between notes. The Iquitos 

 animal sat in a similar posture but looked almost straight downward 

 throughout its performances. This may have been a low intensity 

 indication of a head-down pattern (the animal had not been in its 

 cage very long, and it may have been somewhat shy). A single adult 

 female on Barro Colorado looked downward briefly (and perhaps 

 lowered her whole head) as she uttered Hoots in otherwise typical 

 series, but she always looked up (and perhaps raised her head) be- 

 tween each note of a series. 



These captive individuals were always (with one exception — see 

 page 51) alone in their cages, or at least the only individuals of their 



