- An AI-powered satellite survey has found that the number of wildebeests migrating across Kenya and Tanzania annually might be less than half of the million-plus figure that’s widely touted.
- The authors of the study said their findings underscore the need to calibrate the findings from different surveying methods in order to accurately estimate wildebeest numbers.
- The wildebeest migration is one of the largest mammal migrations in the world, with the animals migrating 800 kilometers (500 miles) in search of better grass.
- Estimating accurate numbers of migrating wildebeests is essential to keep track of the population in the face of habitat loss and increased human presence.
If you’ve watched The Lion King, you probably remember the scene where Mufasa falls into and is trampled by a massive herd of stampeding wildebeests. In real life, as one of the largest mammal migrations in the world, it’s as hectic as it is on the screen.
However, a recent AI-powered satellite survey found that the actual number of wildebeests migrating across the Serengeti-Mara ecosystem might not be as high as the million-plus figure widely cited for the past half-century.
A study published in the journal PNAS Nexus described how a team of scientists used satellite imagery and deep-learning models to find there were “fewer than 600,000 individuals — approximately half the widely cited estimate of 1.3 million wildebeest, which has remained largely unchanged since the 1970s.”
“We’re not trying to say that there’s 700,000 that have died or that they’re missing,” Isla Duporge, one of the lead authors of the study and a postdoctoral fellow at Princeton University in the U.S., told Mongabay in a video interview. “We were surprised to find so many fewer compared to findings from aerial surveys. We’re just opening up the question as to why different methods are producing rather different results.”
Wildebeests, along with zebras and other animals, follow the rains and migrate in a circular path through Kenya and Tanzania. They travel 800 kilometers (500 miles) during each cycle in pursuit of areas with better food and grass. The migration is crucial for the ecosystem as the animals fertilize the soil while on the go. They also serve as an important food source for many predators in the landscape, including lions, crocodiles and hyenas. This makes it critical to keep track of the number of these animals moving through the landscape, especially in the face of increased poaching and a growing human presence.
“It’s important we try to mitigate the tipping point where the birth rate has dropped below a certain number,” Duporge said. “It’s now even more pertinent to develop techniques with which to better track fluctuations in their populations.”
For a long time, aerial surveys were used to count the number of wildebeests. However, the field of view with that technique is restricted, since aircrafts move in straight-line transects, much like a lawn mower. “They count the number of animals they see on the tracks, and then extrapolate that to a much larger area,” Duporge said. “However, with the satellite going on a fixed orbital path, it’s essentially taking a very large snapshot of the Earth’s surface.”
To train the two models, Duporge and her team used 70,000 manually annotated images of wildebeests from another study they’d conducted previously. They then put in a request for satellite images to be captured in the month of August in 2022 and 2023 over an area of 4,000 square kilometers (1,540 square miles).
One model was trained to look for and identify the animal as a whole object. The second model was trained to identify the vertical stripes on wildebeests that shows up as a dark dot in the middle of the animal. “The numbers from both models are quite similar to one another in terms of when you’re looking at this scale of images on the ground,” Duporge said.
Given the large variance between their results and numbers from previous surveys, Duporge said the next crucial step would be to focus on calibrating the two techniques. “We are going to calibrate an aerial survey against satellite survey to work out the relative error biases in both approaches,” she said.
While the ideal approach would be to focus on wildebeests, the challenges in getting permits mean they might focus on another species, likely rhinos, to compare the two approaches.
Meanwhile, Duporge emphasized how the combination of satellite data and AI technology could also be used to gather more nuanced data like collective behavior patterns, herd alignment and aggregation. Training more people in government agencies and wildlife conservation organizations would also help scale up the work even faster, she added.
“I believe it’s the logical thing to be happening now because the temporal and spatial resolutions of satellites are getting so good,” Duporge said.
Banner image: A herd of wildebeests. An AI-powered satellite survey found that the number of migrating wildebeests is much lesser than the widely touted figure of 1.3 million. Image by Charl Durand via Unsplash (Public domain).
Abhishyant Kidangoor is a staff writer at Mongabay. Find him on 𝕏 @AbhishyantPK.
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Citation:
Duporge, I., Wu, Z., Xu, Z., Gong, P., Rubenstein, D., Macdonald, D. W., … Wang, T. (2025). AI-based satellite survey offers independent assessment of migratory wildebeest numbers in the Serengeti. PNAS Nexus, 4(9). doi:10.1093/pnasnexus/pgaf264
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