CHUCK VOCALIZATIONS OF WILD FEMALE SQUIRREL-MONKEYS (SAIMIRI-SCIUREUS) CONTAIN INFORMATION ON CALLER IDENTITY AND FORAGING ACTIVITY

Analysis of the acoustic signal of the chuck vocalizations of adult fe male squirrel monkeys (Saimiri sciureus) in Parque Nacional de Manu, P eru, revealed consistent differences within and between individuals. W e quantified four peak frequency parameters: (a) the peak frequency of single chucks, (b) the first and (c) the second peak frequencies of d ouble chuck, and (d) the peak difference: the difference between the f irst and the second double chuck peaks. One-way ANOVAs and a posterior i comparisons of these variables revealed that each distinguished more than 70% of all possible pairs of females. When all double chuck meas ures were included in a discriminant analysis, 57% of double chuck wer e correctly assigned to the caller. Another category of information po tentially encoded in the acoustic structure of chuck vocalizations is foraging activity. When the chuck of squirrel monkeys during foraging and nonforaging activities were compared, the single chuck peak freque ncy, and the first peak frequency and the peak difference of double ch ucks, were significantly reduced during foraging contexts. Previously Boinski and Mitchell (1992) concluded that chuck facilitate group cohe sion among widely dispersed troop members by providing information of the location of callers; the rate of chuck produced by an adult female increases as she becomes more spatially and visually separated from o ther adult females. The additional information potentially conveyed by chucks on caller identity and foraging activity documented in these n ew analyses further emphasizes the role chuck serve to enhance group c oordination and cohesion.