Some aspects of visual signalling and social organization in the vervet monkey (Cercopithecus aethiops pygerythrus).
This study uses data from three free-ranging and one caged troop to describe the visual signals identified in the South African subspecies of vervet monkey (Cercopithecus aethiops pygerythrus) and to then compare them to those seen at other localities and in other species. It further assesses some signals used specifically by adult males - those involving secondary sexual characters - in terms of male social strategies. In the pursuance of this four aspects of the literature were reviewed in detail. It is concluded that: 1. Natal vervets use fewer visual signals that do other species living in more open habitat. These signals are, however, very similar to those recorded in East Africa, while differing more from those isolated in the West African representitive of the vervet group. 2. Vervet troops are not closed units and migration - both into and out of the troop - occurs frequently. The data suggest that it is a male phenomenon related to the availability of females. 3. The signalling function of the genitals does not accord with that ascribed to them by Wickler (1967). Penile extensions are closely associated with aggressive behaviour by the signaller, and scrotal retractions with submissive behaviour. Associated with these structures are displays that facilitate their presentation to the recipients. 4. While males yawn more than any other age-sex class, largely for social and not physiological reasons, there is no clear evidence that yawns serve specifically to display the canines. Nevertheless, by being strongly associated with certain interactions they are presumed to accrue signal value. 5. As males move into troops where they must compete with unrelated males for the same resources, it is concluded that the genital signalling system has evolved to mediate male relationships. This is of special significance as the "multimale" system of vervets is regarded as being less developed than those of Papio or Macaca monkeys.