Variable initiators of group departure in a cooperative breeder: the influence of sex, age, state and foraging success

For animal species that forage as cohesive units, communal decisions about when to forage and where to go are necessary to maintain group cohesion. While in some species particular individuals or subgroups emerge as consistent initiators of movement decisions, in others, many different individuals initiate coordinated group movements. Theoretical models and some empirical studies suggest that an animal's nutritional need may explain variable leadership. We investigated what individual characteristics influence the likelihood of initiating group departure in the cooperatively breeding banded mongoose, Mungos mungo. We found that initiation of group departure was highly variable, and not influenced by sex or age of individuals. However, during periods of synchronized breeding, lactating females initiated group departure more often than expected by chance. Experiments to test whether nutritional constraints explained leadership roles revealed that the initiators of group departure were deprived individuals. This suggests that low energetic reserves caused by low foraging success can have an influence on the individuals' likelihood of acting as initiators. However, analysis of weight data showed that initiators had neither a lower body weight than when not initiating nor a more negative weight change than other group members. These findings indicate that besides short-term foraging success, other factors such as high energetic demands during periods of lactation, asymmetries in foraging abilities or investment in cooperative activities between individuals also determine leadership. We conclude that while nutritional constraints can influence initiation of group departure, various effects of individual differences may equally affect leadership roles.

► We analyse initiation of group departure in a cooperatively breeding mongoose.
► Initiation was variable, and neither influenced by sex nor by age of individuals.
► However, lactating females initiated group departure more often than expected.
► During experiments individuals deprived of food initiated group departure.
► However, initiators had not a lower body weight compared to when not initiating.