NO. 5 BEHAVIOR OF THE NIGHT MONKEY — MOYNIHAN 8l 



The whole vocal repertory of adult Night Monkeys is composed of 

 discrete units, nine or ten distinctly different types of notes and 

 calls. These patterns do not intergrade with one another to any 

 appreciable extent. Intermediates between different types of notes 

 and calls are comparatively (if not always actually) rare. Complex 

 messages are given in the form of series of different notes or calls, 

 each one of which contains part of the message, not in the form of a 

 single intermediate or ambivalent note or call containing the whole 

 message in itself. This type of vocal repertory is quite different from 

 that of any other monkey whose behavior has been described. It is 

 also quite different from the repertory of infant and young juvenile 

 Night Monkeys. It may be an adaptation to ensure that vocal mes- 

 sages cannot be misinterpreted, even when they are not accompanied 

 by any relevant nonvocal information. In many circumstances, adult 

 Night Monkeys must have to react to, and rely upon, vocalizations 

 alone. 



There may be a general rule, among all monkeys, that species 

 or classes of individuals that are largely dependent upon auditory 

 signals for the regulation of their social behavior tend to have 

 discrete, sharply delimited vocal patterns, while species or classes 

 of individuals that are less dependent upon auditory signals tend to 

 have intergrading vocal patterns. 



Most vocal patterns of adult Night Monkeys are very low pitched. 

 They are lower on the average than those of any related species of 

 similar size. As low-pitched sounds should carry farther than high- 

 pitched sounds, this may be another adaptation to ensure that vocal 

 messages are as clear as possible. The only high-pitched vocal patterns 

 of adult Night Monkeys are short-range signals. 



Some peculiar negative features of the behavior of adult Night 

 Monkeys may be correlated with their slight degree of gregariousness. 

 Unlike adults of many related species, they seldom perform "Allo- 

 grooming" (the grooming of one individual by another) except in 

 copulatory situations, or perform redirection attacks upon other in- 

 dividuals of their own species. They also seem to lack vocal patterns 

 whose primary or only function is to warn other individuals of possible 

 danger in the environment. 



Other distinctive features of the species include : Care of the young 

 by the male (this may be possible only because the sex ratio is one 

 to one and pair-bonds are close and long sustained) ; comparatively 

 frequent use of the hands during fighting (possibly because the 

 canine teeth are small) ; the apparent absence of any tendency to 



