Using unmanned aerial vehicles to estimate the abundance, density, body size structure, and seasonal site use of Caiman yacare in the northeastern Pantanal, Brazil

Wildlife research in natural habitats is essential for understanding natural history; however, substantial financial and sampling efforts are required. Cost-effective methodologies, such as drone applications, can overcome these limitations. Although this approach has already yielded substantial results, applications in studies on crocodilians remain scarce in South America. Given this, the objective of this study was to assess the use of drones in population surveys of Caiman yacare (Daudin, 1802) in bays of Parque SESC Baía das Pedras, northeastern Pantanal. Seasonal sampling was conducted by flying over 7 bays, taking photos, and counting individuals in real time. Water temperature and depth were measured to examine their associations with site use. A total of 1,118 detections were recorded, with the highest counts occurring during the dry season. Total length was estimated for 249 individuals from aerial images, and smaller size classes were the most common. Seasonality strongly influenced the number of caimans detected. Counts were highly heterogeneous among bays. Water temperature was not associated with counts, whereas water depth showed a weak positive association. In addition to providing valuable information on the caiman population in the study area, these results support the use of drones for crocodilian population surveys.