l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



functions. (This does not mean that all patterns that may function as 

 signals are necessarily displays. The head-down and eye-closing pat- 

 terns, for instance, may be functioning as signals when and if they 

 appease, but there is no really convincing evidence that they have be- 

 come specialized to serve such a function. They are not more fre- 

 quent or exaggerated in form than might be expected of pure evasive 

 or avoidance patterns.) 



Following a common convention, the initial letters of apparently or 

 certainly ritualized patterns will be capitalized throughout the subse- 

 quent account. 



The captive Night Monkeys on Barro Colorado Island sometimes 

 began to sway from side to side, instead of retreating or freezing, 

 when they saw a predator or potential predator such as an ocelot 

 or a human being some distance away. The Swaying movements 

 were usually smooth, regular, moderately rapid, and extended over 

 a fairly wide arc (i.e., a Swaying animal would first lean several 

 inches to one side of the vertical and then several inches to the other 

 side). Sometimes an individual would sit on its haunches, grasping 

 its perch with its hands, while it swayed. At other times it might 

 stand up in a more or less extreme preleaping posture. In either case, 

 the head might be kept facing straight forward or turned from side 

 to side, the animal looking right as it swayed to the right and looking 

 left as it swayed to the left. 



Most Swaying was silent ; but sometimes "Gruff Grunts" and/or 

 "Gulps" (see below) were uttered at the beginning and/or toward 

 the end of a bout of Swaying, especially when similar or identical 

 sounds were uttered before and/or after the bout itself. 



An animal performing very brief Swaying sometimes appeared to be 

 doing nothing more than "peering" from side to side to get a better 

 view of the disturbing stimulus ; but most Swaying was much too 

 prolonged and exaggerated and stereotyped in form to be serving 

 this function alone. As exaggeration and stereotypy are characteristic 

 of most displays in most species of animals, it seems probable that the 

 Swaying of these Night Monkeys was ritualized. (The undoubtedly 

 homologous Swaying of some other New World monkeys may be 

 even more exaggerated in form and is undoubtedly ritualized.) 



Unfortunately, the function (s) and, to a lesser extent, the causa- 

 tion of the Swaying of Night Monkeys remain partly obscure, pri- 

 marily because the behavior was never observed in the wild. 



