Using drone-based infrared thermography for monitoring vital signs in dolphins

Monitoring wild animal health is essential for assessing environmental threats. Physiological parameters such as body temperature and respiration rate provide critical insights into an animal's condition but collecting these from free-ranging species is challenging. This study validated drone-based infrared thermography (drone-IRT) as a non-invasive method for estimating dolphin vital signs, evaluating its accuracy, reliability, and practical application. Using a multirotor drone with an integrated thermal camera, we obtained thermographic images of 14 common bottlenose dolphins (Tursiops truncatus) under human care. Flights were conducted in Austral summer and winter at heights of 5 m-30 m, with the camera angled at 0° (zenith) and 50° pitch. Dolphins were either swimming freely or beached. From thermal images, we extracted temperatures based on the heat received from the blowhole, body, and dorsal fin, along with respiration rate estimates. Close-range IRT reference temperatures and environmental variables were recorded throughout each flight. Robust linear mixed-effects models assessed the influence of flight and environmental variables on measurement accuracy and precision. Spearman's rank correlation evaluated the relationship between drone-IRT blowhole temperature and rectal temperature. Drone-IRT measurements closely matched close-range IRT reference values. The most reliable temperature estimates occurred at a combined 10 m and a 0° angle (accuracy: -0.19 °C - 0.08 °C, precision: -0.07 °C - 0.08 °C). The most accurate respiration rate estimates were obtained at 10 m while dolphins swam freely. A weak negative correlation was found between blowhole and rectal temperatures (r = -0.19). This study demonstrates that drone-IRT is a reliable, non-invasive method for monitoring dolphins' surface temperature and respiration rates, but not rectal temperature.