38 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



an escape component, at least at times (see below). Moans also 

 were associated with Gruff Grunts, but relatively rarely. 



It is probable, therefore, that Moans are similar to Low Trills in 

 being produced when both hostile and one or more types of nonhostile 

 motivation are activated simultaneously; but the hostile component 

 seems to be relatively (and probably actually) weaker in the Moans 

 than in all or most Low Trills. 



]\Ioans may also function as appeasement. 



"iXKOMOTORY notes" — GULPS AND SNEEZE-GRUNTS 



These two types of notes are among the most enigmatic and puz- 

 zling of Night Monkey vocal patterns. 



Gulps are very common, probably even more so on the average than 

 Gruff Grunts. They were uttered by all the adult individuals studied 

 during the present investigation. 



A single Gulp is usually moderately loud and always rather "liquid" 

 sounding, rather like a human belch. Sketches of the sound spectro- 

 grams of two typical Gulps are shown in figure IL The mouth remains 

 apparently closed during the utterance of all or most Gulps ; but 

 every Gulp is accompanied by a brief swelling of the throat (to all 

 appearances the same as the inflation accompanying Gruff Grunts 

 described above). 



Gulps are usually uttered in series. A single uninterrupted series 

 seldom includes more than five notes, and series of only two or three 

 notes are quite common ; but series are often repeated rapidly one 

 right after the other, with only brief pauses between successive series. 



An overwhelming majority of all the Gulps heard were uttered by 

 individuals engaged in vigorous locomotory activities. They were 

 uttered during most periods of really active running and leaping in 

 almost all social circumstances. 



One type of performance was particularly remarkable. As noted 

 above. Night Monkeys generally are most active just after sunset 

 and just before dawn. During the predawn periods, the captive ani- 

 mals kept in large cages on Barro Colorado Island usually ran and 

 leapt around their cages rapidly and almost continuously for a half 

 hour or more. Single individuals alone in their cages, mated individ- 

 uals in cages with their mates, and individuals kept together in larger 

 groups, all tended to behave in much the same way at such times. 

 They seldom interrupted their running and leaping to feed or drink 

 or groom themselves, and the individuals that had companions in their 

 cages seldom performed unmistakable hostile or sexual patterns. They 



