Personality of killer whales (Orcinus orca) is related to welfare and subjective well-being

•An evaluation of a questionnaire for killer whale welfare assessment.•Ratings of personality, welfare and subjective well-being were highly correlated.•Questionnaires are a reliable and valid tool for assessing killer whale welfare.•Similarities in correlations with primate studies are probably due to convergence. Questionnaires are very useful tools when it comes to assessing zoo based animal measures and caretakers of these animals (such as keepers, trainers and veterinarians) are in the best position to provide accurate answers to these assessments. Our goal was (a) to empirically demonstrate the utility of a welfare questionnaire and (b) to examine the relationship between three constructs: personality, subjective well-being and welfare ratings, in a sample of killer whales (Orcinus orca) (n = 26). For this purpose, we applied the 4-factor personality structure previously applied to the species, a 4-item subjective well-being questionnaire, and we designed and applied a 39-item welfare questionnaire. The welfare questionnaire was composed by positive and negative welfare indicators related to social and environmental interactions, physical health condition, presence of species-typical and stereotypical behaviors, the capacity to accept situations, and relationships with conspecifics and humans, among others. Each killer whale was rated by an average of 12.5 raters. The mean interrater reliability for subjective well-being and welfare questionnaires was high, and the Principal Components Analysis and the Regularized Exploratory Factor Analysis, revealed one and six factors, respectively. We found some correlations among the three constructs, for instance, Extraversion (r = 0.62, 95% CI 0.02−0.06) and Dominance (r = 0.61, 95 % CI 0.03−0.09) were associated to the subjective well-being factor, while subjective well-being was negatively associated with the Abnormal (r = -0.73, 95 % CI −0.13 to −0.06) and Nervousness (r = -0.66, 95 % CI 0.06−0.17) welfare factors, among others. The welfare questionnaire showed reliable and valid results. Thus, our research represents the first empirical evidence of the utility of assessing the welfare of cetaceans through the use of a multi-trait questionnaire. Therefore, facilities housing cetaceans could use welfare questionnaires to gradually monitor welfare and to intervene if needed. Finally, some of the correlations found closely resembled previous correlations found in primates, which could indicate a possible evolu