NO. 5 BEHAVIOR OF THE NIGHT MONKEY — MOYNIHAN 29 



preceded by barking or loud grunting noises which may be largely or 

 completely homologous with typical Resonant Grunts. At low inten- 

 sities of motivation, male A. palliata may utter series of similar or 

 identical sounds (probably the notes that Altmann calls "male bark, 

 type CI" and "incipient male bark, type C2") without ever breaking 

 into an actual roar. Some of the lowest intensity and softest versions 

 of such series, when heard at a distance, are remarkably difficult to 

 distinguish from the simplest series of Resonant Grunts heard close 

 up. 



The resemblance between the two patterns is so great that the tame 

 male Night Monkey had been uttering Resonant Grunts occasionally 

 for several weeks before I realized that they were not being uttered 

 by the howlers in the adjacent cage. 



It has already been mentioned that the Resonant Grunt perform- 

 ances of this tame Night Monkey were sometimes uttered during or 

 immediately after roars and barks by the adjoining howlers. Possi- 

 bly they were directly released by the sound of the latter. If so, this 

 would help to explain why this Night Monkey tended to utter Reso- 

 nant Grunts in the morning rather than at night. 



The apparent facilitation of Resonant Grunts by the roars and 

 barks of howlers might be additional evidence that the patterns are 

 related to one another. 



(Although individuals of A. palliata may assume Arch Postures 

 while uttering certain types of barks, they apparently do not usually 

 assume such postures while uttering roars or the barks most closely 

 associated with roars.) 



The roars and barks of ^. palliata are certainly hostile. Individuals 

 of this species tend to associate in bands ; each band seems to have its 

 own home range or territory ; and members of different bands usually 

 utter roars and/or barks whenever they come close together (see 

 Carpenter, 1934, and Collias and Southwick, 1952). If the Resonant 

 Grunts of Night Monkeys are provoked by similar stimuli, the rarity 

 of such notes in the forest on Barro Colorado Island may be partly 

 due to the rarity of encounters between different pairs and family 

 groups (see page 10). The roars of A. palliata apparently also func- 

 tion as long-range proclamations of territorial ownership (see Alt- 

 mann, op. cit. ) , and are uttered quite regularly apart from close-range 

 or face-to- face encounters with rivals or neighbors. It seems very un- 

 likely that the Resonant Grunt performances of Panamanian Night 

 Monkeys can serve a similar function with any appreciable frequency. 



(It is possible, however, that some of the same or closely related 

 patterns may do so in other populations of Night Monkeys. Hill, 



