Blood Oxytocin-like Immunoreactivity, Cortisol, and Caretaker-Rated Personality in Captive Bottlenose Dolphins (Tursiops truncatus): An Exploratory Pilot Study

Objective biomarkers related to personality and welfare are lacking for animals under human care. This exploratory pilot study examined whether serum oxytocin-like immunoreactivity (unextracted, unvalidated ELISA) and cortisol are associated with caretaker-rated personality in 11 captive bottlenose dolphins (Tursiops truncatus; nine females, two males; 1.8–29 years). Hormones were measured in residual serum from routine health examinations (2017–2021; 1–7 samples per individual). Four experienced raters scored 25 trait–context items. One dolphin that received intensive treatment contributed the mean of its pre- and post-treatment values. Oxytocin-like immunoreactivity was negatively correlated with cortisol, but not significantly (Spearman’s ρ = −0.57, 95% CI −0.88 to 0.09; p = 0.067), and was nominally significantly and positively correlated with observant ratings toward the physical world (ρ = 0.61, −0.02 to 0.90; p = 0.045) and other dolphins (ρ = 0.68, 0.09 to 0.91; p = 0.022). After Holm or Benjamini–Hochberg correction, none of the correlations between oxytocin and personality remained significant (adjusted p ≥ 0.56), and cortisol was unrelated to personality. Repeatability was high for oxytocin but not cortisol, and the oxytocin–cortisol association depended on one dolphin. These hypothesis-generating findings do not address welfare; validated assays, standardized repeated sampling, and larger multi-facility studies are needed.