Age-Related Regional Thermal Responses to Acute Handling Stress in Canaries (Serinus canaria domestica)

Acute stress represents a major factor influencing animal welfare, triggering rapid physiological and behavioral responses aimed at maintaining homeostasis. Stress-related neuroendocrine changes are accompanied by measurable variations in peripheral blood flow and metabolic heat production, resulting in detectable alterations in surface body temperature. The present study investigated age- related thermal responses to acute handling stress in domestic canaries ( Serinus canaria domestica ) using infrared thermography (IRT), a non-invasive, contact-free technique that allows real-time assessment of physiological changes without additional stress caused by physical restraint or blood sampling. Forty individuals were included and divided into two age groups: juveniles (6 months old) and adults (2 years old). Birds were subjected to a standardized acute stress protocol consisting of three minutes of physical handling. Thermal images were collected immediately before (baseline) and immediately after the stressor, focusing on three thermal zones (TZs): body, periocular area (eye), and beak. Paired comparisons showed that handling was associated with increased surface temperature in most, but not all, thermal zones. Significant post-handling increases were observed in the body region of both juveniles and adults, in the periocular region of juveniles, and in the beak region of adults. In contrast, the increase in juvenile beak temperature and adult periocular temperature did not reach statistical significance. Juvenile canaries showed significant increases in body (P < 0.001) and periocular temperatures (P < 0.05), whereas adults exhibited significant increases in body (P < 0.05) and beak temperatures (P < 0.05). No significant post-handling changes were detected in juvenile beak temperature (P = 0.19) or adult periocular temperature (P = 0.15). Contrary to the commonly reported transient peripheral vasoconstriction typically associated with stress-induced hypothermia, the observed surface temperature changes may reflect a combination of altered peripheral blood flow, activity-related heat production, and stress-associated physiological activation; however, these mechanisms require confirmation using complementary physiological measurements. Overall, the findings support IRT as a sensitive, objective and non-invasive tool for assessing acute handling stress and supporting its use as a complementary tool for animal welfare assessment in birds.