New York, NY, August 4, 2025 — A groundbreaking study by the Wildlife Conservation Society (WCS) and the University of Florida has affirmed the largest known aggregation of freshwater turtles on Earth. The research used drones and innovative modeling to count over 41,000 Giant South American River Turtles (Podocnemis expansa) during a 12-day nesting season along the Amazon’s Guaporé River, also known as the Inténez River.

The study, published in the Journal of Applied Ecology, validates a novel method for estimating wildlife abundance in spatially aggregated populations—such as nesting colonies—by combining drone imagery with statistical models that account for multiple sources of error, including double counts and undetected individuals.

“This is a major leap forward in how we monitor wildlife populations,” said Dr. Camila Ferrara, WCS Brazil aquatic turtle specialist and a co-author of the study. “By using drones and correcting for detection errors, we can now more accurately estimate population sizes and better understand the dynamics of these critical nesting events.”

Added Dr. German Forero-Medina, Science and Conservation Director for WCS Colombia, and a co-author of the study: "With this study we move beyond using drones just to document and photograph this wonderful event, to developing robust and rigorous analytical methods to estimate the turtle population size and its trends over time.”

Traditional ground-based counts are often limited by visibility and logistical challenges. The drone-based approach allowed researchers to create high-resolution orthomosaics—stitched aerial images—of the nesting site, which were then analyzed using a mark-resight method to estimate the true number of turtles.

“This method provides a powerful and scalable way to monitor large, spatially aggregated animal populations with drones—especially in remote areas like the Amazon,” said Ferrara. “By accounting for visibility, movement, and technological artifacts like double counts, we can generate population estimates that are both accurate and reliable. This is critical for effective conservation planning and policy.”

The study’s authors underscore that such an approach is transferable to other wildlife monitoring needs—ranging from migratory birds to marine mammals—where group formations can lead to underestimation or oversight using conventional counting methods.

WCS works with local communities and governments to protect the Giant South American River Turtle and its habitat. Their research is part of larger effort to establish protected areas to safeguard turtle nesting beaches. The species is the largest freshwater turtle in Latin America, reaching three and a half feet (1.07 meters) and 200 pounds (90 kg). The turtles play an important ecological role by dispersing seeds that eventually help regenerate vegetation along river corridors. In addition, they make a significant contribution of biomass to the food web of the river.

###