At least two members of Kenya’s most famous lion pride have died as a result of poisoning, with a further five currently being treated by vets and another missing. Two local herders have been arrested and charged in relation to the incident, marking the first ever prosecutions for wildlife poisoning in the country.

The accused are believed to have deliberately infected a cow carcass with pesticides, which they then left lying around in a region inhabited by the Marsh pride, known across the world for appearing in the BBC’s Big Cat Diary between 1996 and 2008. Among the victims is 17-year-old lioness Bibi, who was discovered “foaming at the mouth, fitting and panting” by BBC wildlife cameraman Mark MacEwan last Sunday, 6 December.

The other dead lion is yet to be identified, after having been disfigured beyond recognition by scavenging hyenas and vultures, some of which have also since died. A lioness named Sienna is currently missing, with Wildlife Direct chief executive Dr Paula Kahumbu mentioning on her Facebook page that “it’s possible that others have died but [their] bodies not found.”

@BBCOne @BBCNews Bibi the oldest lion from big cat diary marsh pride has died due to poisoning, words can't describe pic.twitter.com/8E0i2zAUOO

— Mark MacEwen (@MacEwenMark) December 7, 2015

^{BBC Cameraman Mark MacEwan tweeted this picture of Marsh pride lioness Bibi, who died after eating poisoned meat. Twitter/Mark MacEwan}

Quoted in National Geographic, Marsh pride expert Jonathan Scott explained that conflicts between lions and Masai herdsmen have increased in recent years, largely thanks to government-led changes to traditional land use systems. Whereas the Masai had previously led a nomadic lifestyle with no fixed land ownership, the creation of privately owned plots of land around the borders of the Masai Mara reserve has seen many herders settle with their livestock in the region.

However, as cattle herds have outgrown these small plots, illegal grazing within the confines of the reserve has become increasingly widespread, with “tens of thousands” of cattle being herded into the lions’ territory at night, when no tourists are around. Yet since lions are primarily nocturnal hunters, they have begun preying on the Masai’s animals, often prompting herdsmen to retaliate against them

According to Scott’s blog, “poison has become a major threat to our wildlife”, and has caused considerable damage not only to the Marsh pride but a number of other local species, including the 53 types of birds of prey which inhabit the reserve. Until now, the use of toxic substances to slay animals has gone largely unpunished, yet conservationists such as Kahumbu are hopeful that the prosecution of the men responsible for this latest attack will set a powerful new precedent.

However, poison is far from the only threat posed by local ranchers to the Marsh pride, with Scott claiming that the lions’ territory has been “taken over by herdsmen who swarm all over it at night”. As a consequence, the pride has been largely driven from its former hunting and breeding grounds, which include the Marsh and a watercourse called Bila Shaka – which means “without fail” in Swahili, in reference to the fact that the lions could always be found by safari guides at this spot.

Thanks to the increasing encroachment of settled Masai tribesmen and their cattle, though, Scott laments that “the bottom line is that there is no longer a Marsh pride.”