  In primate groups, collective movements are typically described as processes
dependent on leadership mechanisms. However, in some species, decision-making
includes negotiations and distributed leadership. These facts suggest that
simple underlying processes may explain certain decision mechanisms during
collective movements. To study such processes, we have designed experiments on
white-faced capuchin monkeys (Cebus capucinus) during which we provoked
collective movements involving a binary choice. These experiments enabled us to
analyse the spatial decisions of individuals in the group.We found that the
underlying process includes anonymous mimetism, which means that each
individual may influence all members of the group. To support this result, we
created a mathematical model issued from our experimental data. A totally
anonymous model does not fit perfectly with our experimental distribution. A
more individualised model, which takes into account the specific behaviour of
social peripheral individuals, revealed the validity of the mimetism
hypothesis. Even though white-faced capuchins have complex cognitive abilities,
a coexistence of anonymous and social mechanisms appears to influence their
choice of direction during collective movements. The present approach may offer
vital insights into the relationships between individual behaviours and their
emergent collective acts.
