Table 2.

Glossary definition of characteristics of social complexity (social and cognitive features; see also Table 1)

Characteristics of social complexity	Definition
Social features
Long-term, extended family bonds	Family relationships, which last beyond independence of offspring, including multi-generational family units
Valuable relationships	Unique history of interactions between two individuals, which leads to a broad variation in the quality of social relationships between individuals within groups rendering some individuals more ‘valuable’ than others for each individual in the group. Valuable relationships are characterised by:  • Individuals in close proximity  • High rates of affiliative behaviours (see below)  • Low rates of aggression  • Social support (see below)
Affiliative behaviours	Behaviours, which promote socio-positive relationships between two individuals or group cohesion, e.g. grooming
Coalitions/ Alliances	Individuals that jointly participate in aggressive acts against conspecifics or to gain access to resources form transitory (short-term) coalitions or long-term alliances
Communal Defence	Prey groups actively defend themselves or their offspring by attacking or mobbing a predator, rather than allowing themselves to be passive victims of predation
Communal/ Cooperative Breeding	Cooperative breeding is a social system, characterised by allo-parental care when more than two individuals of the same species provide care in rearing young. Although sometimes used interchangeably, communal breeding is now often applied to cases in which individuals also share reproduction, i.e. when two or more females lay eggs into or rear young within a single nest
Conflict Resolution (Reconciliation, consolation, redirected aggression)	Post-conflict affiliative interactions between former opponents (reconciliation), re-affirmative contacts between the victim of aggression and a bystander (consolation) or an aggressive act by the victim against an uninvolved individual (redirected aggression)
Social support/ social buffering	The stress-reducing effect gained by the presence of (a) social allies (ally)
Cognitive features
Individual recognition (IR)	The ability to distinguish between different individuals either through recognition of actual individually distinctive features (true IR) or class-level cues, such as familiarity, location, kinship (untrue IR). Kin recognition is an animal’s ability to distinguish between close kin and non-kin
Long-term memory	Information, longer lastingly stored in the brain, which is retrievable over extended periods of time
Transitive Inference (TI)	TI is a form of deductive reasoning that allows one to derive a relation between items that have not been explicitly compared before. In a general form, TI is the ability to deduce that: If A > B and B > C, then A > C. In order to be transitive, relations need an underlying scale.
3rd party recognition	The ability to recognize tertiary relationships between conspecific group members, which involve interactions and relationships in which the observer is not directly involved.
Social learning	A process in which the behaviour of others and its consequences are observed and one’s own behaviour is modified accordingly.