Suffering third-party intervention during fighting is associated with reduced mating success in the fallow deer

Numerous studies have shown that dyadic fights are regularly disrupted by the intervention of third-party group members. Empirical and theoretical attention with respect to these interventions have focused predominantly on the fitness advantages that accrue to the intervening individual; conversely, little attention has been given to studying the fitness implications of suffering from third-party intervention behaviour. Therefore, we investigated this issue by examining the relationship between variation in individual mating success and suffering third-party interventions during a fallow deer, Dama dama, rut. Mating success was analysed using a 'hurdle' model against three explanatory variables: daily variation in suffering an intervention, dominance rank and fight rate. The lower, logistic level of the model indicated a negative interaction between variation in suffering an intervention and fight rate in relation to whether a mating was achieved or not. Further investigation of this interaction showed that the proportion of matings achieved by males declined as interventions suffered increased regardless of whether males had a high (five or more fights per day) investment in fighting. There was no meaningful effect observed in the upper level of the model. We also investigated whether there was evidence for a temporal association between suffering interventions and mating success: two models investigated interventions suffered on a previous day and the cumulative sum of interventions suffered over 2 days in relation to mating success. Neither model showed a meaningful association at the lower or upper level indicating that the effects of intervention behaviour are temporally limited in this population. Our results underline the complex nature of the relationships at play during third-party interventions in relation to mating success. We suggest that there is a need for greater empirical investigation and wider theoretical scrutiny with respect to suffering intervention.