NO. 5 BEHAVIOR OF THE NIGHT MONKEY — MOYNIHAN 2/ 



The tame captive male occasionally uttered series of Resonant 

 Grunts which contined to accelerate throughout. In some cases, these 

 series ended in a "bubble" of very, very short rapid notes. In other 

 cases, they accelerated to such an extent that the terminal notes "ran 

 together," to form a continuous or semicontinuous and moderately 

 load "Roar." Both types of accelerated series were uttered in the 

 same circumstances as the simpler series of the same male, in associa- 

 tion with the same other patterns. 



Dr. John H. Kaufmann (personal communication) heard one or 

 more wild Night Monkeys on Barro Colorado Island utter Roars 

 which may have been the culmination of similar accelerated series of 

 Resonant Grunts. These patterns were uttered during a prolonged 

 dispute between two pairs or family groups feeding, or attempting to 

 feed, on a palm tree in fruit. Unfortunately, the postures and move- 

 ments accompanying the notes were not observed. I heard two series 

 of Resonant Grunt-like notes apparently uttered by wild Night Mon- 

 keys on Barro Colorado, again without being able to see the animals 

 while the calls were uttered. The first series was composed of from 10 

 to 15 moderately loud and long bisyllabic grunts, all essentially similar 

 and very low in pitch. The second series followed shortly after the first, 

 and included many more notes. The notes were monosyllabic, and the 

 series rose and fell in pitch at least twice. The general effect was 

 almost singing. These series were probably uttered by one or both 

 members of a mated pair, just before retiring to their sleeping hole 

 at dawn. I could not determine what (if any) external stimuli pro- 

 voked the performances. 



With these few and enigmatic exceptions. Resonant Grunts were 

 not heard to be uttered by wild Night Monkeys on Barro Colorado 

 Island. It is possible that I missed many Resonant Grunt perform- 

 ances (see below), but I was out in the forest frequently enough to 

 establish that such performances must at least be relatively very rare 

 on Barro Colorado. 



The association of Resonant Grunts with Arch Postures, their 

 similarity in sound to undoubtedly hostile Gruff Grunts, and their 

 occurrence during some disputes, would indicate that they are at least 

 partly hostile. Although some Resonant Grunts show a slight resem- 

 blance to Hoots, and the latter are undoubtedly sexual (see below), 

 none of the individuals observed to utter Resonant Grunts appeared to 

 be sexually aroused at the time. They did not perform any overt 

 pairing or copulatory reactions. This would suggest that all Resonant 

 Grunts may be purely hostile. The rarity of Resonant Grunts, the 

 complex forms of the series of such notes, and their close association 



