The combined effects of elevated within-group aggression and inter-group threat on dwarf mongoose behaviour

Within-group aggression has well-established immediate effects on the contest-related behaviour of both participants and other group members (i.e., bystanders). However, we know far less about how within-group aggression influences behaviour not directly related to a contest and how cumulative information from contests can affect later behaviour. Moreover, it is unknown how any such behavioural changes are modified by the threat of inter-group contests, which are likely more costly and require a united response from groupmates, leaving an incomplete picture of how animals balance conflict at different scales. To test how individual and cooperative behaviours are affected by a general elevation in perceived within-group aggression, and how those behavioural responses change when there is an increase in the inter-group threat level, we ran a field experiment with groups of dwarf mongooses (Helogale parvula). Playback of simulated foraging displacements of subordinates by dominants led to bystanders avoiding close proximity with the seemingly aggressive individuals and reducing their cooperative sentinel contributions. The prospect of an inter-group contest (simulated by faecal and vocal presentations of a rival group) caused subordinates to return to close proximity with dominants, but sentinel contributions remained lower on days where elevated within-group aggression was simulated. This work highlights the potentially lasting effects of within-group aggression and how animals balance the threats of conflict from within and between groups.