SHORT AND LONG-RANGE EXCHANGES
Sequential exchanges varied both in the number of participants (callers) and in the degree of dispersion among them. Sixty of the 322 calls were not answered by other individuals. The mean number of calls in an exchange was 4 (sd = 3.4; median = 3; maximum = 31). Participants of the same exchange were sometimes within visual range of one another and sometimes more than 400 m apart.
A one way analysis of variance showed a significant positive relationship between the total number of calls in an exchange and the maximum distance of participants in relation to the focal caller (F(3,239) = 33.12; pFig. 2). Sequential exchanges were associated with both interactions between a few nearby individuals (short-range vocal exchanges) and interactions of larger numbers of individuals spread out over larger areas (long-range exchanges).
Staccatos were mainly produced during short-range exchanges; neighs, particularly those with none or few short elements, were mainly produced during long-range exchanges (c2 = 19.87; df = 3; pFig. 3). As the distance increased, so did the proportion of long elements (F(2,239) = 2.14; p
TONAL AND HARSH STACCATOS
Short elements occurring in staccatos were ordered into 5 types, according to the increasing degree of harshness (tri, t, h, r, p). The percentage of short elements of each type was calculated for staccatos which occurred in one of two feeding contexts: in the "clustered" context, all muriquis fed at the same tree; in the "dispersed" context, individuals fed at different trees. The distribution of short element types between contexts was not random (c2 = 84.26; df = 4; pFig. 4).
SPECIFIC PATTERNS OF NEIGHS
Three patterns of neighs were almost exclusively emitted by receptive females: neighs formed by long tonal emissions alone, neighs formed by the succession of a modulated element with harsh overtones, and neighs that included "trill-sounding" successions of rapid pulses. Another vocal pattern, associated with periods of great group dispersion during group encounters, was formed by a succession of elements that started with a tonal emission and ended with a sudden frequency drop that blended into a harsh, low pitch emission.