Table I.

Central terms of coordination and decision-making research and their respective definitions, selected references, and commentaries compiled by participants of the XXIIIth Congress of the International Primatological Society (IPS) in Kyoto, Japan

Term	Definition	References (selection)	Comments
Combined decision	Members of a group choose individually (but not necessarily independently) between ≥2 actions. They do not aim for consensus, but the combined result of their decisions usually affects the group as a whole.	Conradt and Roper 2005	The distinction between a quorum threshold, e.g., in ants or Tonkean macaques, and a combined decision seems inconclusive. See text for detailed discussion.
Consensus decision	Group members choose between ≥2 mutually exclusive actions to reach a consensus on the group level.	Conradt and Roper 2005; King et al. 2008; Sueur and Petit 2008a,b
Consistent leadership	The same individual always leads group actions.	Conradt and Roper 2005	Opposite of distributed/variable leadership.
Democratic and despotic	A consensus may be reached by the averaging of preferences (democracy), or by following the choices of specific leaders (despotism). Democratic=shared decision-making; despotic=unshared decision-making.	King et al. 2008; King and Cowlishaw 2009	In primatology, we usually use “despotic” and “egalitarian” (or “tolerant”) to characterize the social system of a species and “shared” or “unshared” to describe consensus decisions. See text for detailed discussion.
Follower	An individual that follows/joins the initiator/leader for a certain activity.	Jacobs et al. 2008; Pyritz et al. 2010; Ramseyer et al. 2009a, b, c; Sueur and Petit 2008a,b	The definition of a follower (of a group movement) should be operational and taxon-specific. See text for discussion.
Hidden leadership	The same individual initiates and terminates a group activity (movement), although it is not guiding the movement in front of the group.	Kummer 1968; Pyritz et al. 2010	The new definition of a leader (see below) includes hidden leadership. Therefore, we no longer need this term.
Initiator	The group member that initiates a group activity.	Bourjade and Sueur 2010; Jacobs et al. 2008; Pyritz et al. 2010; Ramseyer et al. 2009a, b, c; Sueur and Petit 2008a,b;	The definition of an initiator (of a group movement) should be operational and taxon-specific. See text for discussion.
Leader	Individual eliciting follower behavior/exerting social influence on others, by its rank into the progression, its behavior, or its social status.	Harcourt et al. 2009; King 2010; Petit and Bon 2010; Pillot et al. 2010; Sueur and Petit 2008a,b, 2010	The definition of a leader should not be restricted by the spatial position during a group movement (Kummer 1968) but comprise the whole process of a collective action. It is also a defining characteristic of a leader that he exerts social influence on conspecifics. See text for detailed discussion.
Mimetism	The probability that an individual performs a behavior depends on the number of individuals already performing this behavior (anonymous mimetism, allelomimetism). It can also depend on the social relationships the individual has with group members already displaying the behavior (selective mimetism).	Camazine et al. 2001; Deneubourg and Goss 1989; Meunier et al. 2006; Petit et al. 2009; Sueur et al. 2009; Sumpter 2006
Overtaking	Followers overtake the individual at the forefront of the group without diverging >45° from the initial trajectory.	Boinski 1991; Erhart and Overdorff 1999; Pyritz et al. 2010; Trillmich et al. 2004
Predeparture behavior	Behavior performed before the departure of the initiator, making the timing of the departure predictable and potentially indicating the direction in which individuals want to move.	Bourjade and Sueur 2010; Sueur and Petit 2008a,b	Other names: preliminary behavior, notifying behavior, voting behavior, intention movement, priming behavior.
Predeparture period	Period preceding the departure of the initiator and delineated by the presence of predeparture behaviors.	Bourjade and Sueur 2010; Sueur and Petit 2008a,b	Other names: preliminary period.
Quorum	Minimum number, i.e., threshold, of group members that need to take or favor a particular action for the whole group to adopt this action.	Bousquet et al. 2010; Franks et al. 2002; Seeley et al. 2006; Sueur et al. 2010; Ward et al. 2008;	In principle, the quorum could be a majority, submajority (less than a majority), or supermajority (more than a majority) of members. In practice, animals are likely to determine whether a quorum has been reached by estimating the relative numerousness of members contributing to the quorum, often by relying on indirect cues.
Recruitment behavior	Behavior that increases the probability that other group members will join a certain activity. It results in a larger number of joiners or in quicker joining of the collective action than when not performed.	Bourjade and Sueur 2010
Self-organizing system	Individual group members follow local behavioral rules, resulting in organized behavior by the whole group without the need for global control.	Camazine et al. 2001; Conradt and Roper 2005; Couzin et al. 2002; Sueur et al. 2009	Emergent properties due to the interactions between individuals in self-organized systems are more complex than the emergent properties that should be observed by the sum of individual behaviors.
Shared consensus decision	All members contribute equally (and independently of individual identity) to the decision outcome. The consensus is usually determined by a quorum or by averaging over all votes.	Conradt and Roper 2005; Sueur and Petit 2008a,b	Opposite of unshared consensus decision.
Terminator	Individual that stops and seems to suggest the termination of a group movement.	Pyritz et al. 2010	Group movements can feasibly comprise 2 linked decisions: 1) initiation: when and in which direction to move and 2) termination: when and where to stop See text for detailed discussion.
Unshared consensus decision	One particular group member, e.g., the dominant, makes the decision on behalf of all group members. All other members abide by this decision.	Conradt and Roper 2005; Sueur and Petit 2008a,b	Opposite of shared consensus decision.
Variable/distributed leadership	Different group members lead group actions on different occasions.	Conradt and Roper 2005; Jacobs et al. 2008; Petit and Bon 2010	Opposite of consistent leadership.
Voting	An individual communicates its individual preference with regard to the decision outcome.	Bousquet et al. 2010; Prins 1996; Sellers et al. 2007; Sueur et al. 2010