This story was updated at 10:01 a.m. and 12:15 p.m. December 8, 2015 to include the latest information on the number of wildlife casualties and the poison used.

First, it was Cecil the lion. Now, there’s news that more famous lions have been killed—this time with poison rather than a gun.

The victims come from the Marsh Pride, a family of lions living in the Masai Mara National Reserve in southwest Kenya. They were the stars of the long-running and hugely popular BBC series called Big Cat Diary. They even have their own Facebook page, where the poisoning was confirmed. On Saturday night, they ate a cow carcass laced with poison.

Five lions in total have been poisoned. Two are confirmed dead: a lioness named Bibi and one unidentified lion, which has been fed on by scavengers. The three others have been treated. Siena, an adult lioness, remains missing. The rest of the pride has been accounted for and are under 24-hour observation. Six vultures, which likely fed on one of the dead lions, have also died.

Bibi was found panting and foaming at the mouth, reported the BBC, which had a wildlife crew at the scene. The two dead lions are underwent necropsies, which turned up traces of the pesticide carbofuran, according to Patrick Reynolds, manager of the nearby Governors' Camp, who mobilized the response.

It is not clear who’s behind the attacks, although authorities have arrested at least two people, who were arraigned in Narok, Kenya, on December 8. In the past, some Maasai villagers have poisoned lions to prevent them from attacking their livestock.

View Images A male lion, part of the Marsh Pride, struggles to breathe and stand on his own after eating a poison-laced cow carcass. Photograph by Patrick N. Reynolds

Part of the reason the Marsh Pride was so popular with the public was that guides always knew where to find them, wrote Jonathan Scott, an English zoologist and coauthor of a book about them, in a blog post. But lately, they’ve been pushed to the fringes of their territory as some Maasai herders allow their cattle into Masai Mara.

Grazing of livestock in the reserve has increased exponentially, even though it’s illegal to do so. A 2009 Journal of Zoology study found that since 1977, it had increased more than 1,100 percent.

There’s a vicious cycle happening, said Anne Kent Taylor, a conservationist at the Masai Mara reserve and a National Geographic Big Cats Initiative grantee. Maasai landowners have seen their grazing lands restricted by land privatization and by agreements with wildlife conservancies, which have a strong record of successful wildlife conservation. In exchange for a considerable stipend, the Maasai agree to sell or set aside some of their land for wildlife conservation and tourism—no grazing allowed. They then use that money to buy more cows, but they have less land for those cows to graze on. The resulting overgrazing means that the herders need somewhere else for their cattle.

During the day, tens of thousands of unfenced cattle graze near the reserve. At nightfall, when the tourists go back to their camps, the animals are herded into the reserve where the grazing is better. That’s the same time that nocturnal predators, including lions, are on the hunt.

“We could have said ‘shocking news’ in regard to the fate of the Marsh Pride—but there is nothing shocking anymore as to what is happening in the Masai Mara,” Scott wrote on his blog. As herds of cattle trampled the grass and shrubs, leaving behind only dirt and dung, the lions have been forced away from the Musiara Marsh, the area where they would rest and breed.

Each year, herders have always killed, either by poison or spear, some lions. “But in the last few years, the situation has escalated beyond all reason,” Scott wrote.

The lions hunt the cattle, and so the Maasai retaliate against the lions.