14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, I46 



as all or most other platyrrhines utter special "Warning Notes" in 

 such circumstances. It is probable, however, that the Night Monkey 

 does have one pattern in its vocal repertory which is at least partly 

 homologous with the Warning Notes of some other species, although 

 uttered in a slightly different range of circumstances and subserving 

 a different function (see discussion on page 43) . 



All the alarm and escape reactions of Night Monkeys would appear 

 to be expressions of the escape tendency alone, in much the same way 

 that the aggressive reactions described above seem to be expressions 

 of the attack tendency alone. The circumstances in which the various 

 patterns occur would suggest that simple freezes are produced by 

 weaker motivation than either active retreat or head-down postures. 

 The strength of the escape tendency may be approximately the same 

 in the latter two patterns, the head-down posture being assumed only 

 by individuals unable or unwilling to retreat, possibly for any one of 

 several different reasons. 



The head-down postures are the most interesting of these patterns 

 from a functional point of view. Both head-downs and ordinary 

 freezes seem to be primarily attempts to hide, and to hide the whole 

 animal, i.e., to prevent a potential opponent or predator from noticing 

 any or all parts of the motionless animal. Some of the head-down 

 patterns may also be advantageous in a slightly different way. When 

 an animal in a head-down posture looks straight downward, its black 

 and white facial pattern and its eyes usually are partly or wholly 

 concealed. These facial features seem to be the characters that release 

 attack most frequently, or toward which attacks are usually directed. 

 Thus an individual in a head-down posture of this type may not be 

 attacked by an opponent or (possibly) a predator, even though the 

 rest of its head and body are perfectly visible, and have in fact been 

 noticed. In such cases, the head-down may function as "appeasement," 

 reducing the attack tendency of an opponent without increasing its 

 escape tendency (see Moynihan, 1955). The closing of the eyes dur- 

 ing some ordinary freezes may subserve a similar function, although 

 presumably less effectively. 



DISPLAY BEHAVIOR 



The most common hostile behavior patterns of Night Monkeys are 

 "displays." 



The term "display" may be used to include all "ritualized" patterns, 

 i.e., all vocal patterns and all movements and postures that seem to 

 have become specialized in form and/or frequency to serve signal 



