White-backed vultureCredit: Daniel Young

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Raptors, Africa’s ‘ecosystem cleaners’ are at risk of extinction due to loss of habitat and prey, according to a study published in Nature Evolution & Ecology.

Led by Phil Shaw from the School of Biology at the University of St. Andrews, in Scotland, and Darcy Ogada of The Peregrine Fund, the researchers measured changes in the abundance of 42 species of birds of prey during surveys conducted in Botswana, Bukina Faso, northern Cameroon, Kenya, Mali, and Niger, between 1969 and 1995 and 2000 and 2020.

A team noted all raptors seen from the road in a stretch of 100 kilometers and recorded how these numbers changed over time.

Of the 42 raptor species examined, 37 had rapidly declined in recent decades, with the population reduction among 29 of these, being steep enough to signal the risk of extinction, the study found.

The decline was more pronounced in west Africa, than elsewhere in Sub-Saharan Africa, an observation, consistent with the severity of threats documented in the region. “From these data, we were able to show that larger raptors have declined more rapidly than smaller species, often at a rate similar to that of vultures,” Shaw says.

The decline rates were more than twice as rapid outside protected areas.

The researchers warned that unless many of the threats facing African raptors are addressed effectively, larger raptor species are unlikely to remain in much of the continent’s unprotected land by the latter half of this century.

“Nearly 90% of raptors found in Africa’s savannah have declined substantially, especially large species like vultures and eagles,” says Darcy, who is The Peregrine Fund’s Africa programme director.

She adds that the secretary bird, which is one of Africa’s most notable species, had declined by an estimated 85%.Risks to large-bodied species are compounded both by their biological traits ( low population density, delayed maturity and low annual fecundity) and environmental factors (large home ranges requiring suitable habitat and increased risk exposure to human impacts), Darcy explains.

“We were surprised that the declines of the larger raptor species — large eagles and the secretary bird — were so high. The fact that African vulture species have declined steeply is strongly linked to illegal poisoning,” Shaw says.

“Other large predatory species – which rely much less on scavenging – should not be so vulnerable to poisoning, and yet had followed a trajectory similar to that of the vulture species.”The larger species are subject to diverse range of pressures however, including land-use change, prey-base depletion and electrocution/collision with energy infrastructure.”

Other, non-vulture species, such as Bateleurs and Tawny Eagles, which rely partly on scavenging, may also become incidental victims. In addition, large raptors, such as the Martial Eagle, are sometimes shot by ranchers.

The researchers note that protected areas in West and Central Africa are particularly underfunded and mismanaged, and high regional levels of poverty and corruption have been linked to adverse conservation outcomes for charismatic mammal species.

Furthermore, the rate of agricultural expansion in West Africa during the 1970s–2000s was more than three times that of Africa as a whole.

In Africa, the loss of the largest and most uniquely adapted avian predators will most likely have the biggest impact on ecosystem function, by limiting prey populations, according to the researchers.

Female Martial Eagles, for example, kill relatively large prey, including small antelope and jackals. Smaller raptors often prey on rodents and seed-eating birds, whose populations are likely to increase in the absence of raptors, potentially causing greater damage to crops.

“But perhaps the most obvious example of an ecosystem service is that of carcass removal by vultures, which potentially limits the transmission of zoonotic diseases to human populations,” Shaw observes.

Ian Newtown, a renowned ornithologist who was not involved in the study, says: “This paper draws attention to the massive declines in predatory birds which have occurred across much of Africa during recent decades.

“The causes of the declines are many – from rampant habitat destruction to growing use of poisons by farmers and poachers and expanding powerline networks – all ultimately due to expansions in human numbers, livestock grazing and other activities.”

The future of Africa’s raptors, according to the researchers, depends on more effective legislation for species protection, enhanced management of protected areas, particularly in relation to tree loss, disturbance at nest sites, poaching and poisoning, tighter coordination between government and conservation stakeholders, and both improved law enforcement and innovative economic incentives to counter persecution.

Additional measures include the protection of nesting trees and cliffs, the global adoption of bio-pesticides for locust control, more effective management of Quelea control operations, and an improved understanding of the corridors and habitats required by migrant raptors. Solutions are also urgently required for the hazards caused by powerlines and windfarms, particularly along migratory flyways.