28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



with periods of intense activity and obvious excitement would suggest 

 that they are very high intensity patterns, produced when the total hos- 

 tile motivation is very strong. They probably are higher intensity on 

 the average than either typical Gruff Grunts or typical silent Arch 

 performances. They certainly appear to be much more closely asso- 

 ciated with, or confined to, periods of intense excitement than either 

 of the latter patterns. Approximately half of the Resonant Grunt 

 performances of the male engaged in disputes with his neighbors were 

 followed immediately by his performing overt attack. The remainder 

 were followed by a variety of ambivalent movements and/or other 

 vocal patterns, all or most of which probably included an escape com- 

 ponent, but never by actual, complete, overt escape. It may also be 

 significant that the only captive individual that uttered Resonant 

 Grunts while obviously aware of being watched was the very tame 

 hand-reared male, the only individual that was not at all afraid of 

 human beings. These facts would indicate that Resonant Grunts are 

 at least as aggressive, on the average, as the most aggressive Gruff 

 Grunts or (more probably) silent Arch patterns. (In other words, the 

 preponderance of the attack tendency over the escape tendency may 

 be as great in Resonant Grunt performances as in silent Arch postures, 

 although the actual strength of both tendencies is greater in the former 

 than in the latter.) The escape component may be almost as minimal 

 in some Resonant Grunt performances as in some overt attack pat- 

 terns, especially the ''deflected" attacks. 



The complete Resonant Grunt performances of the captive male 

 engaged in disputes with his neighbors appeared to function as threat ; 

 but it was impossible to distinguish between the signal effects of the 

 notes themselves and those of the accompanying Arch Postures. 



The Resonant Grunt performances are reminiscent of the most 

 spectacular vocalizations of some other platyrrhine monkeys. In par- 

 ticular, they sound much like some calls of titi monkeys, Gallic eh us 

 spp., and the howler Alouatta palliata. The former have not been 

 studied in sufficient detail to permit discussion of probable homologies 

 and analogies ; but the situation is clearer with respect to the latter. 

 The Roar at the end of some series of Resonant Grunts seems to be 

 strictly homologous with the loud and prolonged vocalization of Alou- 

 atta spp. which is responsible for the vernacular name of the genus. In 

 the case of A. palliata, this is the pattern which Carpenter (1934) 

 calls "type 1 vocalization" and describes as "a voluminous barking 

 roar," and which Altmann (1959) calls the "roar or howl, type Al." 

 It often sounds like nothing more than a much amplified and pro- 

 longed version of the Roar of the Night Monkey, and is frequently 



