Satellite images identify vulture breeding colonies by their droppings

Populations of Rüppell’s vultures have fallen by more than 90% over the past four decades. Knowing exactly where these critically endangered birds breed can allow conservationists to put protective measures in place. But Rüppell’s historically occupied a vast swathe of West, Central and East Africa; finding their remaining colonies is a daunting task.

A team of researchers says it has successfully tested a way to find vulture colonies remotely, pinpointing dozens of potential sites across seven countries using open-access satellite imagery.

The vultures helped.

Like other cliff-nesting birds, their droppings lavishly daub cliff faces below their nests with whitewash. Bulgarian ornithologist Ivaylo Angelov, zoomed in on satellite images of mountainous areas across more than 6 million square kilometers (2.3 million square miles), seeking out cliffs over 20 meters (65 feet) high as well as sites documented in old bird atlases of the region.

Angelov and his colleagues pinpointed 232 previously undocumented nesting sites. Most of these were in Sudan, South Sudan and Chad, but they found others in the Central African Republic, Eritrea, Ethiopia and Somalia.

The work took weeks but was “immensely satisfying.” “I love geography, I love travel, and it was an absolute joy for me to zoom in and check all these incredible mountains,” Angelov says. “I had the feeling that I’m there.”

In the region surrounding Sudan’s Jebel Marra mountains, in the southwest of the country, the team located 36 potential colonies. The Jebel Marra mountains are near the destroyed city of El Fasher in North Darfur state, the site of recent atrocities against civilians by the paramilitary Rapid Support Forces. The satellite imagery that revealed the nests there also provided glimpses into that human suffering.

“Sometimes you see the burnt villages – total destruction,” Angelov says. “I was always feeling very empathetic and sad with the fates of the people.”

The violence there also means the mountains and the vulture colonies they host are out of bounds for Sudanese and other scientists for now.

But where it is possible to carry out fieldwork, such as in South Sudan, an aerial survey confirmed the existence of five colonies found remotely. It also found smaller cliffs with 2-3 nesting pairs that hadn’t been detected. Angelov says this was a happy consequence of his team’s cautious methodology, which deliberately left out potential nesting sites if they had fewer than five large whitewash markings.

In Ethiopia, the method wasn’t as effective in finding colonies. The East African country’s many cliff faces are rugged and sheer and often obscured by shadows that conceal the bird droppings. And with ample nesting sites, vultures in Ethiopia aren’t compelled to nest in large colonies that amass the splodges of whitewash.

Another drawback to the remote detection method is the persistence of old whitewash years after a colony is abandoned, making it vital to visit the colonies in person to prove the birds are still there.

Megan Claase, a co-author of the study who is also conservation manager with African Parks at South Sudan’s Boma and Badingilo national parks, conducted the ground-truthing survey there in December 2024. “We kind of already knew that it [Boma] was a major [breeding] hotspot for the Rüppell’s vulture anyway, just because we’d seen so many colonies around,” she told Mongabay. “But the fact that [Angelov] was finding them from the satellite imagery was really interesting, and it felt quite nice to be able to verify that.”

Not all nesting sites are as safe as the ones found in and around Boma. Out of the 232 potential nesting sites located by Angelov, only 21 were found in protected areas.

And for vultures that breed in South Sudan, which Claase describes as a “safe haven” not yet affected by the scourge of poisoning prevalent elsewhere in the birds’ range, nesting in a national park offers limited protection to a bird with exceptional flying abilities. One Rüppell’s vulture (Gyps rueppelli), among three tagged by African Parks, traveled all the way to Chad and back — a round trip of at least 3,600 kilometers (2,237 miles).

“As soon as they do what vultures do,” Claase says, “and spend most of their time outside of protected areas [they] are exposed to the threats that are inherently there.”

And chief among those threats is exposure to pesticide-laden carcasses, placed either by farmers to poison livestock predators like leopards or hyenas, or by poachers wanting to kill vultures.

Sahara Conservation (SC), an international nonprofit working in central Chad, reports that last year alone its staff found the carcasses of 111 Rüppell’s vultures, and a single lappet-faced vulture, in the space of just six months.

“We’re very aware that if we found that many, it’s very likely that there are others,” Cloé Pourchier, a program officer with SC, told Mongabay in an interview. Almost all the carcasses were missing their heads, suggesting the vultures were poisoned deliberately for belief-based use.

Vulture heads and other body parts are illegally harvested and sold as charms throughout West Africa. Unconfirmed reports suggest poachers could be coming to Chad from neighboring Niger and Nigeria to supply that market, Pourchier says. In the meantime, knowing the location of potential vulture nesting cliffs in Chad will be useful.

“It’s always very good to have information on the national level; just to have an idea of what the population numbers [are],” she says.

Angelov says he believes remote-sensing could be used to find cliff-nesting Griffon vultures (Gyps fulvus) on the Arabian Peninsula, and he’s already experimented a bit to find colonies of critically endangered Indian vultures (Gyps indicus) in India’s Gujarat state.

The ornithologist traces the inspiration for his work to a field trip to Ethiopia and Sudan in 2010. Near Kassala, in eastern Sudan, he and colleagues saw Rüppell’s vultures nesting high up on spectacular cliffs outside the city.

Later, examining satellite images of the same cliffs, Angelov realized the white bird dropping stains beneath the nests were visible from space.

In the years since, satellite technology has advanced dramatically, turning remote detection into a useful tool for conservation.

“The first critical step is to know where the key colonies are,” Angelov says. “You cannot protect a species unless you know where it lives.”

Banner image: A vulture nesting colony on Ngethelewan, an inselberg located on the Boma plateau, in South Sudan. The nesting site, which lies outside Boma National Park, was discovered via satellite imagery and later verified during an aerial survey conducted by African Parks. Image courtesy of Megan Claase.

Africa’s vulture safe zones face tough test across vast landscapes

Citation:

Angelov, I. D., Dobrev, D., Claase, M. J., Fay, J. M., de Bont, M., & Buechley, E. R. (2026). Using satellite imagery to map potential colonies of Rüppell’s vultures (Gyps rueppelli) in Central and East Africa. Ibis, 168(1), 369-376. doi:10.1111/ibi.13454

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