One of nature’s best scavengers is under serious threat in Africa, largely from poison. According to the first analysis of African vultures, populations of seven species have fallen by 80% or more over three generations. Most of these species may qualify as critically endangered. “The rates of decline stand out as being pretty rapid,” says conservation biologist Rhys Green of the University of Cambridge in the United Kingdom, who was not involved in the new analysis. The situation for African vultures, he says, “is not yet irrecoverable, but it is serious.”

Despite their gloomy reputation, vultures provide valuable services. Egyptian vultures (Neophron percnopterus) have been found to remove up to 22% of the waste produced in towns along the Horn of Africa. And by picking clean the carcasses of dead animals, vultures indirectly keep the numbers of feral dogs in check; that, in turn, reduces transmission rates for diseases like rabies.

Worried by reports of vulture declines across the continent, members of the International Union for Conservation of Nature's (IUCN’s) vulture specialist group decided to pull together all the data to figure out the long-term population trends. They reviewed the scientific literature and unpublished data, including road surveys that counted dead vultures.

The situation seems worst for the already small populations of white-headed vultures (Trigonoceps occipitalis)—rare and reclusive birds—which are declining 6.7% per year on average. Three other species are declining between 5% and 6% a year, including Africa’s largest vulture, the lappet-faced vulture (Torgos tracheliotos), the authors report online this week in Conservation Letters.

The main threat appears to be poison. In most reported cases, vultures are the incidental victims of attempts by farmers to kill lions or hyenas by lacing carcasses with pesticides and other toxic compounds. But more and more frequently, vultures are being directly targeted by poachers who presumably don’t want park rangers to notice the birds circling over killed elephants or rhinos. Since 2011, a dozen such incidents have led to more than 2000 vulture deaths in southern Africa. “The scale of it is shocking,” says Darcy Ogada, a conservation biologist with the Peregrine Fund in Nairobi and an author of the paper.

Vultures are also killed for use in traditional medicine. Various parts are thought to bring good luck or ward off evil spirits, whereas eyes and brains are prized for clairvoyance. Vultures are eaten in some African countries, and smoked vulture meat is trafficked internationally. Another significant threat is electrocution from perching on power lines and pylons.

The declines are severe enough that six of the eight species should likely have their conservation status raised from “vulnerable” or “endangered” to “critically endangered,” the authors say. BirdLife International, a conservation group in Cambridge, U.K., is the official IUCN authority for bird statuses and will make its next update in November. “This paper will be an important contribution,” says BirdLife spokesperson Adrian Long.

The most important action to protect African vultures would be for governments to better regulate pesticides and other poisons that kill vultures, the authors say. This has been difficult, Ogada notes. “Management of problem animals is very much dependent on use of poisons,” she says. “It’s poison, poison, poison.” Also important are efforts to upgrade electrical infrastructure to make them safer for vultures. “We hope the paper will wake people up to what’s going on.”