Scientists Just Found 41,000 Turtles Hiding in Plain Sight

Here’s what you’ll learn when you read this story:

A new scientific approach to counting wildlife discovered 41,000 nesting turtles hidden in one area of the Amazon.
A University of Florida team believes they’ve developed a more accurate way to monitor wildlife using drones and statistical modeling.
Wildlife counting is wildly inaccurate with current methods, according to the researchers’ study.

Researchers from the University of Florida have crafted a new process for counting animals. A new research method pairing drones with smart modeling has counted more than 41,000 endangered Giant South American River turtles nesting along the Amazon’s Guaporé River, according to the researchers behind a recent study. It’s the world’s largest known aggregation of freshwater turtles.

This process—revealed in the study, which was published in the Journal of Applied Ecology—involves taking thousands of images to track and study animal behavior in order to remove the errors produced by other methods, such as on-the-ground counting.

Lead study author Ismael Brack—a post-doctoral researcher within the University of Florida Institute of Food and Agricultural Sciences’ School of Forestry, Fisheries, and Geomatics Sciences—called the method “novel,” and clarified in a statement that the method can count many more creatures than just turtles.

The team partnered with the Wildlife Conservation Society in Brazil, Colombia, and Bolivia to test the method by essentially conduct a census of the endangered turtles. These elusive reptiles are exceptionally social animals, and the females congregate annually to nest in the sandbanks of the Guaporé River between Brazil and Bolivia during the summer months.

In the past, scientist used drones and relied on what’s known as the orthomosaic strategy (stitching together hundreds of overlapping aerial photographs) to count turtles, as it’s a quicker and less-invasive approach than counting from the ground. While common, the study explains that the style is subject to detection errors that often get overlooked, and struggles to account for movement during observations.

In the new research, the team used white paint to mark the shells of 1,187 turtles. A drone flew overhead via a planned path four times a day for 12 days to snap 1,500 photos on each pass. The scientists then stitched the photos together, recording the path of each marked turtle, showing where it nested and where it walked. That information allowed the researchers to create probability models to account for turtle movement, all based on seen behaviors.

According to the study, traditional orthomosaic-based counts were shown to be wildly inaccurate, as were the counts taken only from the ground. The new behavior modeling revealed that only 45 percent of turtles using the sandbank were present during drone flights, and roughly 20 percent of those seen walking were counted multiple times (some were counted as many as seven times).

The discrepancies led to observers on the ground estimating that the site contained 16,000 turtles, and observers using the the drone orthomosaic strategy (without modeling) counted 79,000 turtles. When applying the new modeling based on movement, the team estimated the presence of around 41,000 turtles.

“These number vary greatly, and that’s a problem for conservationists,” Brack said. “If scientists are unable to establish an accurate count of individuals of a species, how will they know if the population is in decline or whether efforts to protect it are successful?”

For the plan to work, scientists must understand the movement patterns of animals, which could require clipping seals’ fur, using high-visibility collars on elk, or marking mountain goats with paintball pellets, to name a few examples. The study stated that counting animals when populations are spatially aggregated—such as during breeding or nesting—enhances the accuracy and efficiency of surveying efforts.

The team plans to refine the process, focusing on turtles in other South American countries. “By combining information from multiple surveys,” Brack said, “we can detect population trends, and the Wildlife Conservation Society will know where to invest in conservation actions.”

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