12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, I46 



more important, mated Night Monkeys apparently never redirect 

 attacks upon their mates or young. 



This partial inhibition seems to be one of the more distinctive fea- 

 tures of the behavior of Night Monkeys. It must be advantageous, 

 and it may also be directly correlated with the social structure of the 

 species. Although there is no proof, it seems likely that the pair-bonds 

 of Night Monkeys are comparatively strong and stable. (At least, it 

 is not uncommon to find two Night Monkeys in the same area of the 

 forest, behaving in more or less the same way, for months at a time. 

 It is difficult to believe that the individuals involved are not the same 

 throughout the whole period.) Pair-bonds seem to be weaker and/or 

 less continuous in some other New World primates, such as Alouatta 

 palliata and Cebus capucinus, and the males of such species do per- 

 form redirection attacks upon females and young with considerable 

 frequency (at least in captivity). There may have been strong selec- 

 tion pressure against such behavior in Night Monkeys simply because 

 it is particularly important for them to avoid doing anything that 

 might interfere with the maintenance of their pair-bonds. 



The only redirection attacks observed during the present study 

 were performed by one captive individual on Barro Colorado Island, 

 when it was placed in a cage between two other cages that also con- 

 tain Night Monkeys. When this individual became engaged in a dis- 

 pute with one of its neighbors (fighting through the intervening wire 

 mesh), it would occasionally interrupt the fight to make a rapid and 

 absolutely unprovoked attack upon its neighbor on the opposite side. 



I have never seen Night Monkeys jump up and down in rage, or 

 shake branches of trees, or break off and drop branches, like so many 

 other species of both New World and Old World monkeys (see, for 

 instance. Carpenter, 1934 and 1935, Ullrich, 1961, and Hinde and 

 Rowell, 1962). They may lack such patterns because they are rather 

 small and light in weight. 



Many other species of monkeys perform "play wrestling," all or 

 most of which seems to be a type of partly inhibited attack. This also 

 seems to be almost or completely lacking in Night Monkeys, presum- 

 ably as another consequence of their slight degree of gregariousness. 

 Even when several young Night Monkeys are kept together in the 

 same cage, they do not perform any wrestling which appears to be 

 anything but ordinary, uninhibited attack. 



OVERT ALARM OR ESCAPE BEHAVIOR 

 The simplest alarm reaction of Night Monkeys is a brief "freeze." 

 In the most common form of freeze, an animal remains motionless 



