NO. 5 BEHAVIOR OF THE NIGHT MONKEY — MOYNIHAN 



17 



have been incompletely formed Hoots, uttered without proper ad- 

 justment of the vocal apparatus. 



That this sort of variation is possible is indicated by the behavior 

 of howler monkeys. Male howlers usually utter lengthy roars at dawn. 





Fig. 22. — An infant uttering Squeaks. 



This shows the characteristic shape of the mouth when opened most widely 

 during vocalizations of the Squeak Complex. 



When fully developed, each roar sounds absolutely continuous. But 

 males of the species on Barro Colorado (Alouatta palliata) seem to 

 take considerable time to "warm up," and their first attempts to roar 

 are apt to come out as wooden-sounding rattles (these may be the 

 sounds that Altmann, op. cit., describes as "pops"). 



Infants utter Gruff Grunts which sound quite like the correspond- 

 ing notes of adults and occur in similar hostile circumstances. They 



