Feasibility assessment of commercially available Unmanned Aerial Vehicle sensor and payload functions for crocodile population surveys

In recent years, there has been a growing interest in using Unmanned Aerial Vehicles (UAVs) for monitoring crocodile populations. We therefore assessed the feasibility and effectiveness of using commercially available UAV features for monitoring the population of critically endangered Siamese crocodiles (Crocodylus siamensis) in Crocodile Lake (Bàu Sấu), Nam Cat Tien National Park, Vietnam. The study deployed a DJI Mavic 2 Enterprise Advanced drone with a Smart Controller, a Thermal Infrared (TIR) sensor, a RGB visual camera, and a spotlight payload. The study conducted manual and pre-programmed systematic mission flights above Crocodile Lake to include heterogenous portions of the landscape and to assess variable crocodile detectability over areas of open land, vegetation, and open water. The results of our study show that systematic night flights at 20 m altitude using a DJI dual spotlight at a 45° downward angle, coupled with RGB and co-registered TIR sensors (with continuous gradient palettes on the flight controller) also set to 45° angle, are effective for crocodile population monitoring. Although brief, our study shows that conducting UAV flights in both day- and night-time conditions using TIR, RGB, and spotlight payloads can provide a comprehensive understanding of crocodile population given various strengths and limitations of each. Finally, our experience allows us to provide feasibility recommendations for the use of UAVs to monitoring of crocodile populations in a global context.