- A Nature Ecology & Evolution paper found that of 42 African raptor species, 37 had suffered a population decline over just three generations (up to 40 years).
- Raptors like secretarybirds (Sagittarius serpentarius) stand out among birds thanks to their razor-sharp vision, piercing talons and hooked beaks, making them such effective hunters of everything from other birds to mammals.
- The secretarybird, a charismatic and rare long-legged raptor that hunts on the ground, saw an 80% decline in populations in four African regions.
- The research also highlighted the grave risk to large-bodied raptor populations and the danger of some of the most threatened species being confined to protected areas.
Secretarybirds build their nests high in flat-topped acacia trees to avoid land-bound predators. So when researcher Wesley Gush climbed up those trees to get to their nests, he knew it was a surprise for them. What the nestlings did surprised him too: They played dead, according to Gush.
But a new study warns that the extirpation of secretarybirds (Sagittarius serpentarius) is a very real possibility. Populations of the charismatic long-legged raptors saw an 80% decline in four regions across Africa, researchers estimated, reflecting a broader trend among raptors. These apex predators are disappearing across the continent, leading Philip Shaw, first author of the Nature Ecology & Evolution paper, to warn of an “extinction crisis.”
Raptors stand out among birds thanks to their razor-sharp vision, piercing talons and hooked beaks, which makes them such effective hunters of everything from other birds to mammals. Around 106 diurnal raptor species, those active in the daytime, are known to science from the African continent. Shaw and his colleagues rounded up data on 42 of these raptor species and found that 37 species were on the decline.
“When you start removing raptors, it could have a cascading effect throughout the ecosystem,” he said, “and it’s usually fairly unpredictable.”
The raptors they studied included vultures that feed on carcasses, which may not sound particularly glamorous but is a vital ecological function. Their importance can come home in surprising and disturbing ways. One well-documented case of what happens when raptors vanish comes from India. Vulture populations were nearly wiped out in India between 1992 and 2007 because of the use of an anti-inflammatory drug in livestock that was lethal to the scavenging birds. The absence of the scavengers meant the carrion was left for other animals to feed on. This boosted feral dog populations, which in turn led to a rise in rabies cases.
Secretarybirds are found only in Africa, in some of the most arid habitats. They’re classified as endangered on the IUCN Red List, but the new study suggests they should in fact be considered critically endangered. If the assessment is confirmed, the species would have gone from being of least concern in 2004 to the brink of extinction in the wild in just two decades.
Gush, a Ph.D. scholar at the University of Pretoria, who is studying the secretarybird population in South Africa’s Northern Cape province, said he was lucky to be working with these “cool” birds. They’re less aggressive than other raptors, so his climbs up to their nests were unlikely to result in injury. Plus, they’re fascinating to look at.
The secretarybird has a distinctive crest of quill feathers on the back of its head. (There’s some debate about how the species got its bland-sounding common name, but one explanation suggests their head feathers resemble the goose-quill pens that secretaries in Europe stuck behind their ears.) Sometimes called an eagle on stilts, the secretarybird is a rare bird of prey that hunts exclusively on the ground.
They use their sturdy legs to stomp on their prey — insects, rodents, birds, amphibians or reptiles — with ferocity; they can bear down on their victim with a force five times their body mass. Their varied diet means they’re unlikely to run out of food, but their habitats are disappearing quickly. Grasslands are rapidly being replaced by farmland as population pressures increase across the continent.
Grasslands fall to cultivation more easily than forested areas. Yet even within protected areas, for example in South Africa’s Kruger National Park, woody encroachment on open spaces is eating away into secretarybird habitat.
The birds disperse widely, traveling vast distances. These leggy avians can walk up to 30 kilometers (19 miles) a day. However, this also means they run into human-made hurdles everywhere across their ranges.
“They can cross half of South Africa in a few months,” Gush said. “Unfortunately, that brings them into contact with many threats from power lines to farm fences.”
The specter of climate change is also casting a shadow across secretarybird habitat, which is the focus of Gush’s work. “We are concerned about the increase in temperature in semiarid habitats,” he said. “Even though secretarybirds are well adapted, it might start becoming too hot for them to breed or survive there.”
Though Shaw and his team flagged a broader crisis in raptor populations, the study focused on savanna-based species because they’re better-studied than forest-dwelling birds.
The research relied on four major studies that used road transect surveys from Burkina Faso, Niger and Mali in West Africa, Kenya in East Africa, and Botswana in Southern Africa. The team also incorporated published and unpublished findings from Cameroon in Central Africa.
Shaw said the figures should be considered “best estimates” of what’s going on with these birds. “We just can’t see what’s happening in forests,” Shaw said, adding, “We know forest habitats have been declining, so it’s very likely the remaining species are also showing declines.”
The research also highlighted the threats that large-bodied raptors like secretarybirds and vultures face. Bigger birds have larger home ranges, and disturbances and fragmentation can render them unsuitable. They’re also likely to reproduce more slowly, only a few chicks at a time, so their populations don’t bounce back quickly.
The new study also found that birds do better inside protected areas than outside. But being boxed into protected areas can be a risk, too. Shaw described this as a “double jeopardy.” “They’re not only declining rapidly, but they’re becoming more and more constrained to protected areas,” he said. “They have less territory altogether, but they are also occupying areas that are potentially isolated from each other.”
There’s particular concern about protected areas in West and Central Africa, which suffer graver funding and management problems than the higher-profile protected areas of Southern and East Africa. Some estimates suggest secretarybirds are nearly extinct in these parts of their ranges.
The problem is a wicked one, Gush told Mongabay. It’s easier to turn the reserves into refuges for animals like rhinos and even long-ranging species like elephants. “Birds don’t abide by protected area boundaries. They just kind of go wherever they want to,” Gush said. “You are not getting full protection of a species like an eagle or a secretarybird from a protected area.”
Shaw said expanding protected areas is necessary, but so is better management. Gush suggested that as far as birds are concerned, it’s impossible to conserve everything that falls in their paths. It might be better to have some measure of protection in mixed-use areas that connect designated protected areas by involving people who own or work the land. A “custodianship approach” to conservation is what these birds need, he said.
Banner image: An adult secretarybird on a flat-topped tree. Image by LionMountain via Pixabay (Public domain).
Scientists uncover widespread declines of raptors in Kenya
Shaw, P., Ogada, D., Dunn, L., Buij, R., Amar, A., Garbett, R., … Thomsett, S. (2024). African savanna raptors show evidence of widespread population collapse and a growing dependence on protected areas. Nature Ecology & Evolution, 8(1), 45-56. doi:10.1038/s41559-023-02236-0
Hofmeyr, S. D., Symes, C. T., & Underhill, L. G. (2014). Secretarybird Sagittarius serpentarius population trends and ecology: Insights from South African citizen science data. PLOS ONE, 9(5), e96772. doi:10.1371/journal.pone.0096772