Abstract
Social animals have to coordinate activities and collective movements to benefit from the advantages of group living. Animals in large groups maintain cohesion by self-organization processes whereas in smaller groups consensus decisions can be reached. Where consensus decisions are relevant leadership may emerge. Variation in the organization of collective movements has been linked to variation in female social tolerance among macaque species ranging from despotic to egalitarian. Here we investigated the processes underlying group movements in a wild macaque species characterized by a degree of social tolerance intermediate to previously studied congeneric species. We focused on processes before, during and after the departure of the first individual. To this end, we observed one group of wild Barbary macaques (Macaca sylvanus) in the Middle Atlas, Morocco using all-occurrence behaviour sampling of 199 collective movements. We found that initiators of a collective movement usually chose the direction in which more individuals displayed pre-departure behavior. Dominant individuals contributed to group movements more than subordinates, especially juveniles, measured as frequencies of successful initiations and pre-departure behaviour. Joining was determined by affiliative relationships and the number of individuals that already joined the movement (mimetism). Thus, in our study group partially shared consensus decisions mediated by selective mimetism seemed to be prevalent, overall supporting the suggestion that a species’ social style affects the organization of group movements. As only the most tolerant species show equally shared consensus decisions whereas in others the decision is partially shared with a bias to dominant individuals the type of consensus decisions seems to follow a stepwise relation. Joining order may also follow a stepwise, however opposite, relationship, because dominance only determined joining in highly despotic, but not in intermediate and tolerant species.
Highlights
We found that (i) individuals frequently showed pre-departure behaviour prior to collective movements, the initiator usually chose the direction for which more individuals voted and predeparture behaviour was predominantly shown by adults
We discuss these findings in the context of other macaque studies (Table 2) focusing on (i) the pre-departure period in which individuals can show their preferred travel direction and timing, (ii) the initiation movement of an individual, choosing one specific time and direction for the departure and (iii) the joining of the movement by other group members
Pre-departure behaviour The display of pre-departure behaviour in Barbary macaques is similar to that found in other macaque species [8], [9]
Summary
The majority of the few empirical studies on group coordination in non-human primates conducted in the last decade were carried out in semi-free ranging conditions with ad libitum access to food and in the absence of predators which may diminish true conflicts of interest [6]-[9], but see [10]-[13]. It remains to be investigated whether the same patterns can be found in the wild where failure to coordinate or continued compromises of the same individuals’ interests may lead to an actual cost for group members [12]. The aim of this study was (i) to develop operational definitions of group movement related terms for this species following Pyritz et al [14] and (ii) to investigate the processes underlying group coordination and decision-making in a group of wild Barbary macaques (Macaca sylvanus) to (iii) eventually allow comparisons with other species
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