Red-capped mangabeys (Cercocebus torquatus) adapt their interspecific gestural communication to the recipient's behaviour

Abstract

Sensitivity to recipient's attention and responsiveness are critical markers of intentional communication. Although previous research showed that ape gestures can be intentional, few studies have yet addressed this question concerning monkeys. Here, we characterise the effect of a recipient's presence, attentional state and responsiveness on the interspecific gestural communication of captive red-capped mangabeys (Cercocebus torquatus). Previous reports showed that they produced learnt begging gestures towards a human recipient preferentially when the latter was facing them. We used here a novel setup that allows subjects to move around an experimenter and to use different modalities (visual and acoustic) to communicate. We found that when the recipient was not facing them, mangabeys moved to a position in the visual field of their recipient rather than using attention-getters. Interestingly, unlike apes, they did not elaborate their communication visually or acoustically when the experimenter did not respond favourably to their begging. However, our results may suggest that begging gestures were goal-directed, since mangabeys inhibited them when the experimenter was not available to answer immediately (i.e. give a reward). Overall, red-capped mangabeys' interspecific visual communication presented intentionality features, but their use of begging gestures was less flexible than that of great apes in similar situations.

Figure 1

Experimental setup and procedure. (a) The experimenter was placed in a cubic cage in the centre of the test area and presented a peanut in his hands. The mangabey could thus beg for the reward and move freely around the experimenter. (b) Begging-plates were fixed on two opposite sides of the cage, with two apertures above which it was possible to fix a row of bells so that begging gestures would be audible. (c) The presence and attentional state of the experimenter, as well as his responsiveness (i.e. rewarding behaviour) varied with the experimental condition.

Figure 2

(a) Number of begging gestures produced and (b) time spent away from the ‘begging side’ of the cage (in seconds) in relation to the experimenter’s presence and attentional state. Individual data are plotted as means of sessions A and B. C− experimenter absent, C+ experimenter facing reward and subject, HU head up, BT body turned, BTP body turned and opaque plate blocking begging apertures in front of the experimenter. GLMM negative binomial was used to analyse the number of begging gestures (a) and LMM to analyse the time spent away from the ‘begging side’ of the cage (b). Different lower-case letters indicate significant differences between conditions (P < 0.05).

Figure 3

Begging gestures produced by mangabeys in relation to number of gaze alternations between the experimenter and the reward in the positive control condition.

Figure 4

Upward gazes in relation to the experimenter’s presence and head position. Individual data are plotted as means of sessions A and B. C− experimenter absent, C+ experimenter facing reward and subject; HU: Head up. GLMM Poisson: ***P < 0.001; ns non-significant difference.

Figure 5

(a) Begging gestures and (b) proportions of lesser (Beg−) and amplified (Beg+) begging gestures when the experimenter did not answer. Individual data are plotted as means of sessions A and B. NR.a: first 10 s; NR.b: last 10 s. GLMM Poisson was used to analyse the numbers of begging gestures and LMM to analyse the proportions of lesser and amplified begging gestures. ***P < 0.001; ns non-significant difference.

Figure 6

(a) Number of begging gestures and (b) proportion of lesser (Beg−) and amplified (Beg+) begging gestures when the experimenter gave a wrong response. Individual data are plotted as means of sessions A and B. WR.a: first 10 s; WR.b: last 10 s, after a false response. GLMM Poisson was used to analyse the number of begging gestures (a), and LMM to analyse the proportion of lesser and amplified begging gestures (b). ***P < 0.001; *P < 0.050; ns non-significant difference.