NO. 5 BEHAVIOR OF THE NIGHT MONKEY — MOYNIHAN 43 



It seems probable that the Sneeze-grunts were produced by some 

 combination of locomotory and escape tendencies similar to that 

 producing Gulps. It was noticeable, however, that Sneeze-grunts were 

 most likely to be uttered just before or just as an individual made a 

 long leap, while Gulps were relatively more frequently associated 

 with shorter leaps and running movements. Similarly, when wild 

 Night Monkeys were encountered in the forest, they sometimes 

 uttered Gulps when approached in the dark, switched to Sneeze-grunts 

 when a light was put on them, and then retreated in overt escape. 

 Such facts would suggest that the Sneeze-grunts may have been 

 produced when the escape tendency was stronger than in all or most 

 Gulps. 



The Sneeze-grunt is the only Night Monkey pattern similar to the 

 ordinary Warning Notes of many other New World monkeys in 

 form. It resembles the latter in being loud, sharp, and usually single. 

 It may well be phylogenetically related to the Warning Notes of other 

 species, and may have functioned in the same way in the ancestors of 

 the Night Monkey, alerting other individuals of the same species to 

 possible danger in the environment and inducing them to escape. It 

 does not, however, seem to function in this way at the present time. 

 Its signal effect is obscure at present ; but it may be another contact 

 note like the Gulps. 



DISCUSSION 



The preceding list includes almost all the typical vocal patterns of 

 adult Night Monkeys.^ It may be useful, therefore, to add some gen- 

 eral comments about their vocal repertory as a whole. 



Adult Night Monkeys do utter vocalizations which are more or 

 less obviously intermediate between otherwise distinct types of notes. 

 Some of these intermediates have been mentioned above ; others in- 

 clude intermediates between Moans and Gruff Grunts, between Gruff 

 Grunts and Gulps, and between Sneeze-grunts and Gruff Grunts. 



Although some of these intermediate vocalizations are uttered with 

 appreciable actual frequency, they seem to be comparatively rare, and 

 are uttered relatively less frequently than intermediate notes in the 

 repertories of adults of some related species, e.g., species of Saimiri, 



3 Some brief experiments with an ultrasound detector would indicate that 

 neither the adults nor an infant kept in captivity on Barro Colorado uttered any 

 calls or notes completely inaudible to the htmian ear. In this respect, Night 

 Monkeys seem to differ from at least one other species of New World primate, 

 the Pygmy Marmoset (Cebuella pygmaea). 



