Around half a dozen lions belonging to the Marsh Pride on the Masai Mara National Reserve in Kenya became sick on Monday after eating cow carcasses that had been laced with poison — that latest incident in an escalating conflict between herdsman and animals living within protected areas, said conservationists.

"They started falling all over the place and frothing at the mouth," said conservationist Anne Kent Taylor, who lives in the Masai Mara several months of the year.

One of them, a well-known lioness Bibi, died from the poison. Another lioness, Sienna, is missing and presumed dead. The rest of the lions were treated quickly and their prospects for recovery were good, Taylor said.

Kenyan authorities arrested three Masai herdsman for the alleged poisoning of Bibi and her pride after the lions killed two of their cows, the Associated Press reported. A fourth suspect remains at large.

Bibi gained notoriety after appearing on the BBC's "Big Cat Diary" between 1996 and 2008.

Bibi, unlike the lion Cecil, which was killed by an American dentist earlier this year, wasn't poached for sport or sale, but was almost definitely killed by local Masai herdsmen.

Taylor said that livestock provide the Masai herdsmen with sustenance along with a system of status and trade.

"It's their wealth," she said, "The way you and I would put money in a bank, they put it into cattle."

Lions and the Masai's cattle graze on the same land, which has been privatized and converted into conservation areas where cattle are often forbidden. Taylor said the government supports the establishment of conservation areas because it promotes tourism

"[The Masai] have been asked to put their land into conservancies in order to make these areas safe for wildlife," Taylor said. "And they receive money from the management of the conservancy. So they are beneficiaries of the tourism industry."

As a result of the booming tourism industry centered on the conservation of wildlife, the Masai herdsman are effectively being pushed off their land.

"The cattle size has increased exponentially and the grazing has shrunk exponentially, that's what causes the conflict," Taylor said.

The use of poison as a means of killing or sickening lions is on the rise in several East African countries, said Phillip Henschel, a lion specialist at the conservation group Panthera.

"Poachers killing wildlife for their body parts also increasingly use poison, as has been widely documented in the case of the cyanide poisonings of elephants in Zimbabwe," he said. "But in the case of the lion, most known cases of poison attacks could be linked to herdsmen."

The conflict between lions and livestock in Africa is particularly intense in Tanzania, Zimbabwe, Kenya, and parts of Namibia.

Veterinarians performed an autopsy on Bibi and determined the lion was killed with the pesticide carbofuran, which is sold under the brand name Furadan and is banded in the United States, Canada, and the European Union.

Up to 100 lions are killed every year with poison in Kenya, according to Henschel.

"Pastoralist tribes across Africa have always killed lions in defense of their livestock," Henschel said. "But while the traditional hunts using spears or bow and arrow demanded bravery and were usually targeting individual problem animals, increasing numbers of herders across Africa use poison as a preventive measure to locally exterminate entire large carnivore populations."

The Kenyan NGO Wildlife Direct has lobbied since 2009 for Kenya to impose a ban on the pesticide, but the Kenyan government has so far refused to do so.

Follow Hannah K. Gold on Twitter: @togglecoat