30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



1960, cites several descriptions and transcriptions of calls uttered 

 by South American Night Monkeys which may be Roars or typical 

 Resonant Grunts or similar notes. There are enough records of such 

 calls to suggest that they may be common among South American 

 populations. It is conceivable that the typical Resonant Grunts and/or 

 the Roars are becoming "obsolescent," in process of disappearing, 

 among Panamanian Night Monkeys.) 



Some of the Resonant Grunt performances of Panamanian Night 

 Monkeys may function as "triumph ceremonies" in certain circum- 

 stances. The performances by captive individuals after being dis- 

 turbed or irritated, when the cause of the disturbance was leaving or 

 had left, appeared to be "proclamations" of the fact that the perform- 

 ing individuals had defended their territories successfully. 



(It is possible that Night Monkeys have some sort of "territorial 

 motivation," a tendency which is satisfied by the possession of a terri- 

 tory, in addition to the ordinary attack tendency (see page 53). This 

 might be involved in the causation of some Resonant Grunt perform- 

 ances. If so, it might help to explain why Resonant Grunt perform- 

 ances in which escape seems to be minimal do not always lead to 

 immediate attack.) 



Intermediates between typical Resonant Grunt and typical Gruff 

 Grtmt performances do occur, but apparently are always rare. I 

 heard such intermediates only three times. All took the form of series 

 of notes. Each note was similar to an ordinary Gruff Grunt in loud- 

 ness and tone, but the successive notes of each series first rose and 

 then fell in pitch in much the same way as in typical Resonant Grunt 

 performances. One series of this type, including a great many notes, 

 occurred in the same dispute in the forest on Barro Colorado Island 

 in which typical Resonant Grunts also were heard. It was not possible 

 to see the postures and movements accompanying this performance. 

 A similar series was uttered by one member of a captive pair on 

 Barro Colorado when disturbed by some stimulus (possibly an oce- 

 lot ?) outside its cage. This was uttered from a crouch posture. Sev- 

 eral shorter series were uttered by the mate of the captive male who 

 uttered typical Resonant Grunts while engaged in disputes with his 

 neighbors. She usually started a series just after the male had begun 

 a series of Resonant Grunts, or just after he had finished — ^thus pro- 

 viding a peculiar "echo" to his performances. Her series were uttered 

 from typical Arch Postures, with both hands and feet grasping a 

 perch. 



