Supplementary material from "Ontogeny of rake mark scarring on common dolphins (Delphinus delphis): insights to aggression and affiliation?"

Résumé fourni par la source

Aggressive and affiliative interactions shape resource allocation, social structure and reproduction in social species. In delphinids, rake marks (parallel scars from tooth raking) indicate social interactions. When examined alongside ontogeny, demographic traits and scar position, rake marks can inform social dynamics. We examined rake marks on common dolphins (Delphinus delphis) in Aotearoa New Zealand (2006–2024; n = 102) during post-mortem examinations to explore drivers of social behaviour. Using a zero-inflated generalized linear mixed model, we assessed rake mark occurrence (probability of rake density > 0) and prevalence (rake density, rake marks dm−2) across the body (n = 101; dorsal/ventral, cranial/caudal, left/right) in relation to sex, age, total body length, sexual maturity, body condition (n = 101) and female reproductive status (n = 51), to infer confrontation, avoidance and lateralization. Females showed higher rake mark prevalence but lower occurrence than males, suggesting infrequent but prolonged interactions, possibly sexual coercion. Resting mature females exhibited the highest rake mark prevalence and occurrence, potentially related to reproductive availability. Rake prevalence and occurrence increased with total body length. Age, sexual maturity and body condition were not strong predictors of rake mark occurrence or prevalence. Our findings highlight rake marks as potential indicators of social dynamics.

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