8o SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



to the terminology used here. (His account would suggest that the 

 individuals that he studied were either young or adults which had 

 retained juvenile characteristics.) The patterns which he calls "waver- 

 ing squeaks," "sharp calls," and "booms" are not precisely identifiable, 

 although the latter two (at least) would appear to belong to the Grunt 

 Complex. 



One further comment may be added. There may be some geo- 

 graphic variation in the form of some vocal patterns of Night Mon- 

 keys ; but it seems unlikely that the differences between the patterns of 

 different populations or subspecies are as great as might be inferred 

 from some of the published accounts. 



SUMMARY 



This is the first in a series of papers on the social signals and some 

 other behavior patterns of New World primates. 



Night Monkeys are moderately small. Under natural conditions, 

 they are purely arboreal and nocturnal. In Panama, at least, they are 

 not very gregarious. They are seldom found in groups larger than a 

 single family of two adults and one young, and even mated individuals 

 may stray some distance apart from one another. 



The hostile behavior of adult Night Monkeys includes unritualized 

 attack and escape movements and a variety of ritualized displays. A 

 few of these displays are special postures and movements, i.e., visual 

 signals, but the great majority are notes and calls, i.e., auditory signals. 

 The sexual behavior of adults includes olfactory and tactile signals in 

 addition to unritualized patterns and a few auditory signals. 



Some of the most distinctive features of this display behavior seem 

 to be direct or indirect consequences of, or adaptations to, nocturnality. 



Adult Night Monkeys have fewer visual displays than any other 

 platyrrhines whose behavior has been studied. The few that they do 

 have are relatively crude, produced by simple movements of the whole 

 head and/or body. Some of their visual displays are less exaggerated 

 in form that the homologous patterns of related species. They do not 

 have any facial expressions, or erectile tufts or ruffs of hair around 

 the face which could be used in signaling. It seems likely that they 

 have lost, or failed to develop, an extensive and complex system of 

 visual signals simply because they frequently cannot see one another 

 clearly in the forest at night. 



As partial compensation, they utter "contact notes" more frequently 

 than other platyrrhines. These may help to maintain social cohesion 

 between the adult members of a family group in the dark. 



