Measuring body size and condition in live cetaceans is challenging, particularly in the wild. Drones change that. But have you ever wondered how accurate drone-based photogrammetry really is? Our new study shows that UAV-based photogrammetry provides accurate and precise estimates of body size, body condition, and even body mass. We validated these measurements against direct data, supporting drones as a reliable, non-invasive tool for marine mammal research and conservation 🐬. Check out the study: https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP290419 ABSTRACT: Accurate morphometric measurements are essential for estimating body size and condition in animals. These characteristics are, in turn, key to eco-physiological studies, wildlife management and conservation. For free-ranging cetaceans, however, collecting non-invasive morphometric data is challenging. Unoccupied aerial vehicle (UAV) photogrammetry offers a promising solution but requires ground-truthing to assess accuracy and precision. Similarly, morphometric-based indices of body condition must be validated against the animals’ true body condition. Here we validated UAV-derived estimates of body size and condition in bottlenose dolphins (Tursiops spp.) under human care by comparing photogrammetry-based measurements of body length, width, height and girth from both stationary and swimming individuals with manual measurements. The two methods showed negligible differences, with UAV-based data yielding lower variability, confirming both high measurement accuracy and precision. Using UAV-derived measurements we calculated a volume-based body condition index (BCI) and compared it with a mass-based BCI, a standard metric in ecological research. The two indices showed a near-perfect fit, demonstrating that volume-based metrics reliably reflect true body condition in small cetaceans. Body density decreased with increasing body condition, consistent with higher fat-to-muscle ratios. By combining UAV-derived body volume with predicted density, based on their body condition, we accurately estimated individual body mass (mean error = 6.4%). This study provides a comprehensive validation of UAV-based photogrammetry to estimate body size, condition and mass in small cetaceans, highlighting its value as a non-invasive and cost-effective tool for ecological and conservation research. Riccardo Cicciarella PhD Candidate Department of Evolutionary Anthropology, University of Zurich Winterthurerstrasse 190 8057 Zurich, Switzerland Twitter:@RiccardoCiccia1 Shark Bay Dolphin Research – Monkey Mia – Useless Loop | Western Australia (sharkbaydolphins.org)<https://www.sharkbaydolphins.org/><http://www.sharkbaydolphins.org/dolphin-alliance-project/>