NO. 5 BEHAVIOR OF THE NIGHT MONKEY — MOYNIHAN 3 



belongs to the subspecies griseimemhra. The exact provenance of the 

 animals in the National Zoological Park in Washington, D.C., was 

 unknown. The animals observed in Iquitos supposedly were caught in 

 nearby areas and, therefore, were presumably representatives of the 

 nominate subspecies ( Hershkovitz, op. cit.) or the possibly distinct 

 subspecies vociferans (Cabrera, 1957). 



All references to the behavior of other platyrrhine monkeys in the 

 following pages are based upon personal observation, unless specifi- 

 cally stated otherwise. 



GENERAL HABITUS, LOCOMOTION, AND FEEDING 



Some characteristic activities of Night Monkeys in the wild have 

 been described in a number of earlier publications. The best general 

 survey is by Cabrera and Yepes (1940), who summarize the reports 

 of many early naturalists and travelers in South America; and the 

 best account of Night Monkeys in Panama is by Enders (1935). It 

 may be useful to recapitulate some of this information, and add a 

 few details about locomotory and feeding habits, before discussing 

 other aspects of behavior. 



Night INIonkeys differ from all other "true" monkeys in being 

 almost completely nocturnal. Both captive and wild individuals are 

 most active immediately after nightfall and just before dawn. 



Wild Night Monkeys sometimes start to become active in the 

 evening before it is completely dark, and may continue to move about 

 for some minutes after it has started to become light in the morning. 

 Captive individuals easily learn to move about in the daytime, and 

 their adjustment to continuous artificial light at night is usually 

 rapid. They appear to see quite well in all but the brightest light. This 

 is not surprising, as there is some evidence (see, for instance. Hill, 

 1957, and Rohen, 1962) that the nocturnal habits of Night Monkeys 

 are specialized rather than primitive among Platyrrhini. (The terms 

 "primitive" and "specialized" are used, throughout this paper, as 

 defined by Simpson, 1961.) 



Wild Night Monkeys apparently are purely arboreal. On Barro 

 Colorado Island, they usually move and feed in trees at heights 

 ranging from 20 to at least 100 feet above the ground, and apparently 

 never come lower than 10 feet above the ground. During the daytime, 

 they sleep in holes in trees. 



The fur of Night Monkeys is very thick and soft. This softness 

 may be an adaptation to nocturnal and arboreal habits, possibly 

 helping to reduce or muffle the sound of movements. It is probably 



