A contextual, and spectrographic representation of the acoustic repertoire of Callicebus cupreus was first given by Moynihan (1966), who described 10 vocal signals in three different categories according to their frequency (high, medium and low pitch) and loudness (table 1.2). He also described two non-vocal signals: ―sneezes‖ and ―gnashing‖. Following this study, Robinson (1979a) provided additional description of acoustic signals of the same species. By measuring the climax of some loud calls, Robinson put forward a finer differentiation of the C. cupreus repertoire with 13 acoustic signals, instead of 10 (see table 1.2). Apart from the ―infant distress calls‖, all vocalisations are produced by both juveniles and adults (Moynihan, 1966, Robinson, 1979a).
According to both authors, most vocalisations of C. cupreus were repeated to form phrases and combined into short or long sequences that were used in different contexts (Moynihan, 1966, Robinson, 1979a,b). By playing back artificially constructed male loud call sequences, Robinson (1979a) also showed that monkeys were sensitive to call order, as they produced more moans in reaction to the abnormal sequence (Robinson,
1979a). The most studied vocal behaviour of Callicebus monkeys is ‗duetting‘, long and loud sequences of calls uttered by the mated pair in a coordinated way. Duets can be produced spontaneously or in response to the duets by other breeding pairs, a behaviour that seems to function in delineating or enforcing territorial boundaries (Moynihan, 1966, Kinzey et al., 1977, Kinzey, 1981, Kinzey and Robinson, 1983, Robinson, 1979b, Robinson, 1979a, 1981, Robinson et al., 1987, Müller, 1995a,b, Müller and Anzenberger, 2002).
Apart from the study of duets, very little work has been conducted on titi monkey vocal behaviour and little progress has been made concerning the function, meaning and context-specific use of their vocal utterances. Virtually nothing is known about their vocalisations in the predation context. This apparent lack of interest goes beyond the need for increasing the knowledge about titi monkeys‘ vocal behaviour. Most primates vocalise when threatened by a predator and the study of these alarm signals have proved particularly valuable for examining the cognitive processes in non-human animals (Zuberbühler, 2006). Additionally, the study of alarm calls has attracted the attention of many different disciplines (including physics, linguistics, anthropology and sociology) particularly interested in the origins of language and semantic signalling (Fitch, 2010).
Table 1.2. Description of the vocal repertoire of Callicebus cupreus.
Call Type: Moynihan (1966) Call type: Robinson (1979a) Context/Situation of use High pitched, quiet vocalizations
Squeaks, Whistles and Trills Squeaks, Whistles and Trills During intra-specific disputes and fights; when other groups are calling; during movements towards the sound source; when seriously disturbed by the observer.
- Chirps (low intense chirrups) When foraging in the presence of an observer. No apparent response from others.
Screams Screams1 Considered as similar pattern of squeaks, whistles and trill, although much louder than, and often intermediates, between whistles and trills. Robinson heard only twice from wild animals. One following fighting between two young non-resident males in the presence of a non- resident female. The other was when one female leapt back after apparently encountering something in a tree. The male approached rapidly and both animals gave Chirrup-panting simultaneously
Sneezes2 Sneezes Following chases between monkeys of different groups; During rapid avoidance of an observer. Some are autochthonous (attempts to clear the nasal passages).
- Infant distress calls Especially if disturbed by the observer‘s presence; if they are unable to negotiate a difficult crossing; the male often approaches and allows the infant to mount.
Medium pitched
Chirrups Chirrups3 Chirrups are uttered in a wide variety of social circumstances; when locating and recognizing group members to foster group cohesion; common during boundary encounters and disturbance from the observer‘s presence.
Chuck Chirrups3 Chucks are more common in obviously hostile situations. Mainly in disputes among captive animals and as reactions to the sight or sound of humans, and in some territorial boundary disputes in the wild. It may function as alarm or warning calls when uttered as reactions to humans.
Low pitched, loud vocalizations
Moans Moans During boundary interactions and after leaving the Sleeping tree. Moans usually introduce duets to ensure that the mates are in close proximity.
Before moving towards the boundaries and following rest periods.
Resonating notes Pants Occur in phrases as part of longer sequences; Pants are sexually dimorphic, male can be heard 500m away and female can be heard 50m away; May be uttered by isolated individuals but are more common in compound songs during vigorous and prolonged disputes.
Resonating notes Honks Occur in phrases as part of longer sequences. Honks are given between phrases of pants during duetting.
Resonating notes Bellows Occur in phrases as part of longer sequences. The loudest in the repertoire; Occur in male and female solo sequences and duetting sequences.
Grunts Grunts4 Occasionally produced before and after duetting during intergroup interactions
Pumping notes Pumps Occur in all sequences with the exception of the short ―chirrup-panting‖ sequence described by Robinson (1979a).
1
Screams were classified as loud low-pitched vocalisations by Robinson (1979a).
2
Sneezes were described as a non-vocal signal by Moynihan (1966).
3
Chirrups were classified as loud, low-pitched vocalisations by Robinson (1979a).
4