Three lions died this week in southwestern Kenya after eating a poison-laced cow carcass, Wildlife Watch reported. Those lions, and five others also poisoned, come from Masai Mara National Reserve’s Marsh Pride, which starred in the popular BBC series called Big Cat Diary.

The lions might be the best known victims of this incident, but they’re not the only ones. Eleven endangered white-backed vultures also died after feasting on poisoned carcasses—and these deaths underscore a huge problem. In Africa and elsewhere, poison has contributed to the population decline of these scavengers, whose importance is often overlooked because of their perceived ick factor.

“Across the board, it’s the biggest threat worldwide,” says Darcy Ogada, assistant director of African programs for The Peregrine Fund, an Idaho-based nonprofit dedicated to saving birds of prey. She's the author of a study published in June that attributed more than 60 percent of 7,800 vulture deaths recorded across 26 African countries to poisoning.

The populations of eight of the continent’s vulture species have fallen by an average of 62 percent, the researchers found, and four of Africa’s species are considered critically endangered by the International Union for Conservation of Nature, which determines the conservation status of the world’s animals.

Much of the time, vulture poisonings in Africa are unintentional. In this most recent instance, it’s believed that Maasai herders intended to poison the lions in retaliation for their attacks on livestock.

In some cases, however, ivory poachers use poison to kill elephants or lace their carcasses specifically to eliminate vultures so they won’t circle overhead and reveal the poachers’ presence. A study published Monday in the journal Oryx revealed that between 2012 and 2014, about 150 elephants and more than 2,000 vultures were killed in nearly a dozen poaching-related incidents in seven African countries.

States of Decline There are 23 species of vulture divided into two families by hemisphere, New World and Old World, each facing threats. Number of species None 1 8 NORTH ASIA EUROPE AMERICA AFRICA SOUTH AMERICA AUSTRALIA AMERICAS: RECOVERING AFRICA: DECLINING INDIA: CRASHED When counts of California condors began in the early 1900s, the birds’ ranks had already been decimated. After decades of conservation efforts, numbers are growing, but lead poisoning from spent ammunition in scavenged carcasses is still a threat. Poisoned by herders aiming to protect their livestock and by poachers afraid that circling vultures will give away their location, some groups are shrinking by as much as 50 percent a decade. Traditional healers believe vulture brains grant the ability to see the future. India’s populations plunged in the mid-1990s. Hindu belief prohibits consumption of beef, so cows that die are disposed of outdoors. Vultures died of kidney failure after eating cows that had been treated with the bovine drug diclofenac. The drug was banned in India in 2006. California Condor Population Birds Counted in India Transect Surveys Causes for Decline in African Vultures 2012 235 1992 2007 1% Killing for food 1950 150 9% Electrical infrastructure 2000 vultures wild condors Killing for traditional medicine 29% 2012 169 1967 1 -96.8% captive 61% Poisoning Indian and Slender-billed 0 -99.9% White-rumped MATTHEW TWOMBLY, LAUREN C. TIERNEY, CHIQUI ESTEBAN, NG STAFF SOURCE: DARCY OGADA, PEREGRINE FUND; SIMON THOMSETT, NATIONAL MUSEUMS OF KENYA; STEVE KIRKLAND, U.S. FISH AND WILDLIFE SERVICE; BIRDLIFE INTERNATIONAL; VIBHU PRAKASH, JOURNAL OF THE BOMBAY NATURAL HISTORY SOCIETY, 2007 States of Decline There are 23 species of vulture divided into two families by hemisphere, New World and Old World, each facing threats. Number of species None 1 8 AMERICAS: RECOVERING When counts of California condors began in the early 1900s, the birds’ ranks had already been decimated. After decades of conservation efforts, numbers are growing, but lead poisoning from spent ammunition in scavenged carcasses is still a threat. California Condor Population 2012 235 1950 150 wild condors 2012 169 1967 1 captive AFRICA: DECLINING Poisoned by herders aiming to protect their livestock and by poachers afraid that circling vultures will give away their location, some groups are shrinking by as much as 50 percent a decade. Traditional healers believe vulture brains grant the ability to see the future. Causes for Decline in African Vultures 1% Killing for food 9% Electrical infrastructure Killing for traditional medicine 29% 61% Poisoning INDIA: CRASHED India’s populations plunged in the mid-1990s. Hindu belief prohibits consumption of beef, so cows that die are disposed of outdoors. Vultures died of kidney failure after eating cows that had been treated with the bovine drug diclofenac. The drug was banned in India in 2006. Birds Counted in India Transect Surveys 1992 2007 2000 vultures -96.8% Indian and Slender-billed 0 -99.9% White-rumped MATTHEW TWOMBLY, LAUREN C. TIERNEY, CHIQUI ESTEBAN, NG STAFF SOURCE: DARCY OGADA, PEREGRINE FUND; SIMON THOMSETT, NATIONAL MUSEUMS OF KENYA; STEVE KIRKLAND, U.S. FISH AND WILDLIFE SERVICE; BIRDLIFE INTERNATIONAL; VIBHU PRAKASH, JOURNAL OF THE BOMBAY NATURAL HISTORY SOCIETY, 2007

It's not only vultures in Africa that die from poisoning. In Asian countries such as India, cultural attitudes contributed to a mid-1990s population plunge described as the “Asian vulture crisis.” Hindus revere cattle, Ogada says, so deadly sick cows were given diclofenac, a painkilling drug, to ease suffering. But diclofenac can kill the vultures that feed on dead cows. The drug is also used in Spain, home to 95 percent of Europe’s vulture population, according to The Guardian. And in North America, lead poisoning from spent ammunition in scavenged carcasses still threatens California condors (yes, they’re vultures), whose numbers have been growing since 1987, when the species went extinct in the wild.

Although they’re not winning any popularity contests, vultures are ecologically important. Their highly evolved digestive systems allow them to eat diseased carcasses and not get sick. Without them there’s a greater chance that disease could spread, Ogada says, because other scavengers such as hyenas or, in the case of urban settings, feral dogs, aren’t as well adapted.

That’s what happened in India, where feral dogs replaced vultures as the main scavengers, and rabies cases exploded. David Allan, curator of birds at the Durban Natural Science Museum, told National Geographic in July that because of that, health care costs climbed by an estimated $34 billion in India between 1993 and 2006.

But Ogada thinks there’s reason to love the birds beyond this service: “They’re cool. They’re squabbling, they’re kicking—they’re so charismatic,” she says.

Unfortunately for vultures in Masai Mara Reserve, human-lion conflict has been on the rise as land subdivisions and privatization reduce grazing land for cattle. At night, some Masai are known to allow their cattle into the reserve, where the grazing is better—and illegal, explained Anne Kent Taylor, a conservationist at the reserve and a National Geographic Big Cats Initiative grantee.

In this week’s incident, a pesticide in the highly toxic carbamate family likely killed the vultures and lions, though the poison won’t be revealed until lab testing concludes. Carbamates such as carbosulfan and carbofuran, which is banned in the European Union and effectively banned in the United States, have often been used to poison wildlife.

View Images This vulture died after feeding on a poisoned cow carcass. It’s believed that Maasai herders intended to poison lions in retaliation for their attacks on livestock. Photograph by Charlie Hamilton James

In 2009, though, the Philadelphia-based manufacturer of carbofuran, marketed under the trade name Furadan, held a buyback program to remove the product from Kenya after CBS’s 60 Minutes linked it to lion deaths in Masai Mara.

African countries need to curtail the easy access to highly toxic pesticides and other poisons, Ogada believes. “The abuse of pesticides goes far beyond poisoning wildlife,” she says in a National Geographic blog post.