Across Africa, vultures are electrocuted by power lines or crushed by wind turbines. Their brains are ground to snuff by witch doctors who believe the substance has magical powers. They die after eating pesticide-laced carcasses intended for lions and other predators.

As a result, vulture populations are plummeting.

Africa's eight vulture species have declined in number by an average of 62 percent during the last 30 years, according to the first estimates of a continent-wide decline in the large birds . Six of those species would likely be considered critically endangered by the International Union for Conservation of Nature.

While vultures are not cute and cuddly, they are one of nature's most important scavengers—a flock can strip a carcass in a matter of minutes, said study leader Darcy Ogada , assistant director of Africa Programs for the Peregrine Fund, an Idaho-based nonprofit dedicated to saving birds of prey. ( Read more about Ogada's work in her own words .)

But Ogada predicts these natural recyclers, which breed slowly and need years to mature, could be extinct in Africa in the next 50 to 100 years.

"The impact of their declines are huge," Ogada says, whose research is funded by National Geographic . "They're providing such a huge service to such a huge population."

Tracking the Birds

In 2012, Ogada and colleagues extensively reviewed scientific literature on Africa's vulture populations, as well as unpublished data from road surveys and counts of dead vultures.

The team analyzed the data by assigning a vulture species in each country to one of four categories: extinct or in severe decline, strong decline, moderate decline, or no decline.

Of the 95 vulture populations they examined, 85 (or 89 percent) were either nationally extinct or had experienced severe declines, according to the study, published recently in the journal Conservation Letters .

The scientists also studied the major threats to African vultures based on data from published and unpublished articles, as well as media reports, drawn from 1961 to 2014.

That work revealed that poisoning from eating pesticide-laced carcasses caused as many as 60 percent of the vulture deaths recorded since the 1970s.

View Images Sixty-six vultures lie dead after eating poisoned carcasses in Limpopo, South Africa, on May 7, 2015. Photograph by Andre Botha

When a large predator such as a lion kills livestock, a farmer will sometimes sprinkle poison on the carcass to kill the predator in retaliation, a practice that's illegal but rarely prosecuted. Vultures usually get to the corpse—and the poison—first. (Related: " Lions, Hyena Killed With Poisoned Meat .")

Pesticides are poorly regulated and abused in Africa, adds Ogada. Usually sold as "lion killer" in several African countries, many farmers don't know what the chemicals are really used for.

Vulture Threats

David Allan, curator of birds at the Durban Natural Science Museum in South Africa, studies Cape vultures in South Africa. He says these vultures have largely disappeared from commercial farming areas in the country where pesticide use is routine.

But there are various threats beyond pesticides, he notes.

Vulture Rehabilitation Watch: Cape vultures recover from injures and poisoning at a rehabilitation center in South Africa.

Rapid urbanization in parts of Africa has displaced vultures from their habitat. A massive growth in wind farms across the continent is also a concern—the birds often collide with the turbines.

Vultures are also also targets for poachers, who sell their parts to people who use witchcraft. The birds are known for their tremendous eyesight, and many believe their body parts can be used to see into the future. Relatively little is known about the illegal and secretive trade. (See " An Awareness of Vultures in Our Poisonous World .")

The scavengers also die after feeding on carcasses left behind by poachers. Illegal hunters poison the corpses to throw off law enforcement, which use circling vultures as a beacon for illegal activity.

In July 2013 in Namibia, Ogada came across what she called a horrific scene: About 500 dead vultures surrounded a pesticide-laden elephant carcass. Poachers had poisoned the birds and left their bodies to rot.

Troubling History

The impacts of disappearing vultures may be devastating in developing countries of Africa, where disposing of potentially harmful carcasses is left to nature, Ogada notes.

As an example, look no further than India, Allan says, where vulture populations collapsed by more than 96 percent in the 1990s. (Related: " Many Asian Vultures Close to Extinction, Survey Finds .")

Poisoned by diclofenac, a drug used to treat sick livestock, India's vultures died en masse of liver failure. Without the aerial cleanup crew, feral dogs took up the role as scavengers. As the dog population exploded, so did diseases such as rabies— of the 55,000 annual rabies deaths worldwide, 20,000 occur in India .

The cost to public health was enormous: Healthcare costs climbed by an estimated $34 billion in India between 1993 and 2006, according to Allan.

Ogada says the same could potentially happen in West Africa, where human populations are high and vulture populations are dismally low.

The first step, Ogada says, is for governments in Africa to regulate pesticide use, for instance by creating a registry that can limit the amounts a person can buy at one time.

She and other researchers have also hosted programs on pesticides' dangers for local people in Africa.

"It can start in one country and hopefully snowball to other regions," she says.