Understanding contest skill to reduce the welfare costs of aggression

Abstract Skill is the ability to do a challenging behaviour well. We examined how contest skill influences contest success, costs and whether skilful behaviour enhances welfare. We measured skill across three domains: accuracy, appropriateness (selecting suitable agonistic tactics when the optimal choice varies) and efficiency, alongside vigour, sex and body weight. Skill was weakly correlated across domains. Winners were heavier relative to their opponent, displayed greater vigour and were more skilful at blocking, but other skill measures did not predict contest win/loss outcome. Appropriate blocking by winners reduced the number of lesions received by reducing exposure to attacks, suggesting it can both reduce costs and improve competitive success, with potential welfare benefits. Losers received more lesions when they adopted appropriate postures after submission; however, this unambiguous submission may have resulted from more costly contests. For winners, being heavy relative to the opponent tended to reduce skin lesions received, but otherwise, having a weight advantage did not reduce contest costs. Fighting with increased vigour led to a considerable increase in contest costs, particularly in losers. Compared to other resource-holding potential traits, skill has moderate effects on winning and injuries but nevertheless modulated energetic costs of fighting.