Every year, along the stretch of river that forms the border between Brazil and Bolivia, something extraordinary happens. Thousands of female Amazon giant river turtles haul themselves onto the sandy riverbanks to lay their eggs — a gathering so ancient that it predates modern civilisation by millions of years.
Scientists have always known the gathering was large. They didn't know it was this large.
A 2025 study by researchers from the University of Florida and the Wildlife Conservation Society (WCS), published in the Journal of Applied Ecology, revealed what drone technology alone could show: more than 41,000 Amazon giant river turtles nesting together along the Guaporé River — the largest freshwater turtle nesting aggregation ever documented in science.
How They Counted Them
Traditional ground surveys of large turtle colonies are inherently flawed. Researchers move through the habitat slowly, disturbing animals and inevitably missing individuals. Statistical models based on ground counts often dramatically underestimate populations.
The team took a different approach. They deployed drones to fly multiple passes over the nesting beaches during a 12-day window, capturing thousands of high-resolution aerial photographs. The images were stitched together into composite maps, and to reduce the risk of counting the same individuals twice as turtles moved on and off the beach, researchers marked more than 1,000 individual shells with white paint to track re-encounters and calibrate their statistical models.
The result: a count of more than 41,000 female turtles at a single site — a number that almost certainly underestimates the true total once males, juveniles, and submerged individuals are considered.
Why the Guaporé River?
The Guaporé River — known as the Itenez in Bolivia — runs through a remote and relatively protected region of the southwestern Amazon basin. Indigenous and traditional communities in the area have lived alongside the turtles for generations, and in recent decades, collaborative conservation programmes between communities, governments, and NGOs have helped reduce poaching of both eggs and adults.
The Amazon giant river turtle (Podocnemis expansa) is one of the world's largest freshwater turtles, reaching up to 90 cm in length and weighing up to 90 kg. It plays a critical ecological role in the Amazon as a seed disperser and nutrient cyclist — moving nutrients from river to forest and back again as part of the ecosystem's circulation.
Once dramatically reduced by commercial hunting for meat and eggs, the species has shown signs of recovery in areas where protections have held. The discovery of this 41,000-strong aggregation is one of the most powerful pieces of evidence yet that sustained conservation works at scale.
A Monitoring Revolution
Beyond the conservation news, the study demonstrates what drone-based wildlife monitoring can achieve. The ability to count tens of thousands of animals accurately — without disturbing them — opens possibilities for tracking populations of many large, nesting species that have historically been impossible to survey reliably.
The team plans to expand drone-based monitoring across other major nesting areas along the Amazon's tributaries, with the goal of building the first comprehensive population census for the species across its entire range.
Forty-one thousand turtles. One riverbank. A species that was almost gone — and clearly isn't.
Sources: University of Florida News · Wildlife Conservation Society (WCS) · Journal of Applied Ecology (2025) · Mongabay · PBS Nature · Popular Science · Discover Wildlife
