Diana monkey long-distance calls: messages for conspecifics and predators

Primate long-distance calls have typically been interpreted as communication signals between conspecific groups (the ‘resource defence hypothesis’), but their potential role as anti-predator alarm calls has received comparably little attention. Male diana monkeys, Cercopithecus diana diana, in the Taï forest of Côte d’Ivoire often utter long-distance calls, either spontaneously or in reaction to a variety of stimuli, including predators and non-predators. The present study focuses only on predation contexts and provides evidence for communication to both predators and conspecifics. Males called only in response to predators whose hunting success depends on unprepared prey, that is, leopards and crowned hawk eagles, but not in response to pursuit hunters, such as chimpanzees and humans, which can pursue the caller in the canopy. Calling was regularly combined with approaching the predator. Both observations suggest that male long-distance calls are used to signal detection to the predator (‘perception advertisement hypothesis’). Analysis of male long-distance calls given to leopards and eagles showed that they differed according to a number of acoustic parameters. The two call variants were played to different diana monkey groups; conspecifics responded to them as though the original predator were present. We conclude that, in addition to their function in perception advertisement, diana monkey long-distance calls function as within-group semantic signals that denote different types of predators. ? 1997 The Association for the Study of Animal Behaviour A number of forest dwelling primates, including the diana monkey, Cercopithecus diana diana, have strikingly loud vocalizations known as loud calls or long-distance calls (Gautier & Gautier 1977; Snowdon 1986). The long-distance calls can be heard over distances that are typically greater than the diameter of the home range (Tenaza & Tilson 1977; Whitehead 1989). Spectral energy is concentrated at frequencies between 100 and 1000 Hz (Whitehead 1987). Attenuation in the upper forest strata is low in this frequency range, leading some to hypothesize that calls within this range are particularly well suited for longdistance communication (Wiley & Richards 1978; Richards & Wiley 1980; Waser & Brown 1984). Thus far, most functional explanations of primate long-distance calls have focused on their role in intraspecific communication (Byrne 1982; Kinzey & Robinson 1981; Sekulic 1982; Snowdon Correspondence: K. Zuberbühler, Department of Psychology, University of Pennsylvania, 3815 Walnut Street, Philadelphia, PA, 19104-6196, U.S.A. (email: [email protected]). 0003–3472/97/030589+16 $25.00/0/ar960334 ? 19 589 1986; Tenaza 1989; Gautier & Gautier 1977; Waser 1978). For example, long-distance calls mediate spacing, increase group cohesion and alter the movement of groups in the grey-cheeked mangabey, Cercocebus albigena (Waser 1975), the eastern black-and-white colobus, Colobus guereza, the blue or Sykes’ monkey, Cercopithecus mitis (Waser 1977), the yellow-handed titis, Callicebus torquatus (Kinzey et al. 1977), the dusky titis, C. moloch (Robinson 1979; 1981), and the cottontop tamarins, Saguinus oedipus (Snowdon et al. 1983). Functional Hypotheses Table I lists possible functions of primate longdistance calls. In the one-male groups of diana monkeys, only the adult male produces longdistance calls (Hill 1994). Females, in turn, utter other call types that are not used by the male. During the pilot phase of the study (January– September 1991), diana monkey males produced long-distance calls in different contexts, such as 97 The Association for the Study of Animal Behaviour Animal Behaviour, 53, 3 590 after a long-distance call of a neighbouring male, after a tree fall, in reaction to the presence of a crowned hawk eagle or without any apparent stimulus. Long-distance calls as resource defence signals Primate long-distance calls have repeatedly been interpreted as sexually selected signals used in male contests (‘resource defence hypothesis’: Sekulic 1982; Tenaza 1989; Mitani 1990; see Andersson 1994 for the application of this hypothesis to bird song). We assume that the ‘resource defence hypothesis’ can also explain a substantial proportion of the long-distance calls given by male diana monkeys. Here we focus on a less acknowledged function of long-distance calls in the avoidance of predation. Long-distance calls as detection signals to