Drones revolutionize animal counting and conservation efforts
08-04-2025

Drones revolutionize animal counting and conservation efforts

Wildlife conservation often depends on simple but vital numbers. How many animals are left? Where do they gather? Are their populations growing or shrinking?

In the dense forests and winding rivers of the Amazon, answering such questions is far from easy. A team of researchers from the University of Florida has found a better way to count animals.

Their method, which uses drones and statistical models, confirmed the largest known nesting site for Giant South American River Turtles. The site lies along the Guaporé River in the Amazon, shared by Brazil and Bolivia.

Researchers counted over 41,000 turtles in one nesting season. This effort improves how scientists monitor threatened species.

“We describe a novel way to more efficiently monitor animal populations,” said Ismael Brack, a postdoctoral researcher at UF/IFAS and lead author of the study.

Turtles under pressure

The Wildlife Conservation Society (WCS) works across South America. It monitors the Giant South American River Turtle, a species under pressure from illegal hunting. These turtles are known for their social nesting behavior.

Every year in July or August, females gather to lay eggs on sandy banks. This seasonal event creates a rare chance to count them. Brack met WCS scientists at a conference and learned about their drone-based methods.

The team used orthomosaics – detailed images stitched from hundreds of aerial photos. These allow a wide view of nesting areas without disturbing the turtles.

Drone counts often miss animals

Counting animals from drone images is fast and non-intrusive, but it has limits. Traditional counts assume all individuals are visible and counted once. That’s rarely true.

Animals can leave or arrive during flights. Some may hide or appear multiple times. Marks on animals may also be obscured by dirt or shadows. To fix this, researchers used a modeling approach that corrects several common counting errors.

The method accounts for open populations, where animals come and go during the survey period. It also adjusts for movement-based double counts, where the same animal appears more than once in images.

The model considers that some individuals may be unavailable during drone flights, and it includes cases where identifying marks on animals are not visible. The team painted 1,187 turtles with symbols and tracked sightings over 12 days.

Tracking how animals move and nest

The model used two core datasets: daily counts and repeated sightings of marked turtles. It assigned individuals to three states – walking, nesting, or gone.

By modeling how animals transitioned between these states, the team estimated true presence and visibility. The average turtle had a 36.9% chance of nesting each day.

Only about 35% of turtles present overnight were seen by the next morning. Just 11.8% of marked individuals stayed visible the following day.

Model fixes animal count mistakes

Double counts caused major inflation. Roughly 20% of walking turtles appeared more than once. Some showed up seven times. About 22% of turtle marks were obscured and couldn’t be identified.

These corrections changed the results significantly. Ground teams counted nearly 16,000 turtles. Simple drone image counts (without corrections) gave a total near 79,000. The new method placed the number around 41,000.

“These numbers 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?”

Wider value for conservation science

The model adapts easily. It can support surveys of birds, seals, elk, and more. If animals are marked or tracked in some way, the approach adjusts for visibility, movement, and presence.

For example, seals may be clipped, elk wear collars, and goats marked with paint. The method could include GPS tags to track movement and avoid overcounts.

Different states – like nesting, feeding, or resting – can be defined depending on the species. This allows the model to capture time-based changes in animal behavior.

Drones can improve animal counts

Researchers suggest marking individuals throughout the study, not just at the start. This captures changing patterns better. Surveys should cover the full aggregation period.

Skipping days between surveys can work, but only if the population turnover is low. When many animals come and go daily, shorter gaps give better data.

Ground observers missed many turtles, especially when numbers were high. Turtles block each other from view. Drones don’t have this problem. Images from above show the entire nesting site.

This gives researchers a repeatable, standardized method to compare counts over time. It reduces animal stress and is less invasive than catching or fencing turtles.

What’s next in animal counting 

Brack and colleagues suggest expanding the surveys. Some turtles nested after the study ended. Nearby sandbanks may host others.

The new method could estimate total regional populations by including more sites and longer timeframes.

“By combining information from multiple surveys, we can detect population trends, and the Wildlife Conservation Society will know where to invest in conservation actions,” Brack said.

This drone approach opens new paths for monitoring wildlife with accuracy, efficiency, and care.

The study is published in the Journal of Applied Ecology.

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