Third-party intervention behaviour during fallow deer fights: the role of dominance, age, fighting and body size

Third-party interventions of dyadic contests are often explained by appealing to high-level cognitive processes such as coalition formation between group members. However, alternative accounts that do not appeal to sophisticated cognitive processes have been proposed. We tested predictions from two such models using the fallow deer, Dama dama, as the model taxon: (1) a random target model that argues that intervention is directed randomly towards a target and (2) a specific target model that assumes that targeting is directed at contestants that have low resource-holding potential. Contrary to predictions of the specific target model, we found no evidence that targeting following third-party intervention increased as the resource-holding potential of the target declined. Both models argue that intervention serves to prevent individuals from gaining a winner effect and advancing up the hierarchy. Being targeted did not result in a decline in dominance rank, although targeting was associated with investment in dominance-related fighting tactics. Fight intervention was associated with an increase in rank early in the rut and accounted for increased mating success. Therefore, interveners benefited beyond simply preventing rivals from advancing in the hierarchy. In theoretical terms, a random target as opposed to a specific target model explains intervention behaviour in the fallow deer.