The hippopotamus is one of the most dangerous animals in Africa. This is precisely the reason their actual numbers are hard to count. Elusive amphibious mammals, they surface only sporadically. So researchers are turning to optical technology to capture the activity of hippos when it may be difficult to monitor them from the ground. Some observers have taken to using elaborate costumes to try to blend in and prevent aggression from the large animals. Researchers at the University of New South Wales (UNSW) have found that studying the animals can be just as effective when humans are not there at all. A UNSW study shows that using a drone to film hippos in Africa is an effective, affordable tool for conservationists to monitor the threatened species’ population from a safe distance, particularly in remote and aquatic areas. Courtesy of Victoria Inman. “Even though hippos are a charismatic megafauna, they are surprisingly understudied, because of how difficult it is to work with nocturnal, amphibious, and aggressive animals,” said lead author Victoria Inman, a doctoral candidate at UNSW Science. To track the number of hippos in a specific region in Africa, the researchers used a drone, the multirotor DJI Phantom 4, which has a 12.4-MP CMOS camera capable of video and still photography, to film the hippos and estimate their numbers in regions where they are most active. The research compared hippo counts from drone footage to land counts, both taken over seven days at a lagoon with a resident hippo population in the Okavango Delta in northern Botswana. The researchers found that the drone method was just as accurate as the land surveys in estimating hippo numbers. “The bird’s-eye perspective the drone gave us made it a lot easier to differentiate between individual hippos, even when they were crowded together,” Inman said. The lower the drone flew, Inman said, the clearer the resolution. “Counting from 40 meters above was the best method and about 10% more accurate than land surveys,” she said. Another advantage of using the drone — beyond the researchers not being eaten — was that the footage allowed measurement of the hippos’ body lengths to determine their ages, an important factor in quantifying population trends. “This method will be important for monitoring the age structure of hippo populations in different parts of Africa and to track breeding,” said co-author professor Richard Kingsford, supervisor and director of the Centre for Ecosystem Science at UNSW Sydney. The researchers were able to effectively track changes within a hippo pod over time as adults emigrated from the lagoon to new locations. “Drones also provide a viable alternative to land-based counts and have low impact on hippos, offering further opportunities to survey inaccessible areas and, just as critically, collect this information safely,” Kingsford said. The study shows that small commercially available drones are a simple, affordable, and effective method of collecting data, Inman said. The technique could be used to routinely monitor pods in various river systems, which could provide far greater insight into seasonal changes and the long-term patterns and statuses of hippo populations.