Experimental field evidence that out-group threats influence within-group behaviour

In social species, conspecific outsiders present various threats to groups and their members. These out-group threats are predicted to affect subsequent within-group interactions (e.g. affiliation and aggression) and individual behaviour (e.g. foraging and vigilance decisions). However, experimental investigations of such consequences are rare, especially in natural conditions. We used field-based call playbacks and faecal presentations on habituated wild dwarf mongooses (Helogale parvula)—a cooperatively breeding, territorial species—to examine post-interaction responses to the simulated threat of a rival group. Dwarf mongooses invested more in grooming of groupmates, foraged closer together and more regularly acted as sentinels (a raised guard) after encountering indicators of rival-group presence compared to control conditions. These behavioural changes likely arise from greater anxiety and, in the case of increased vigilance, the need to seek additional information about the threat....