Mass deaths of hundreds of elephants in just two months have rocked the southern African nation of Botswana - but scientists are still weeks away from working out what's behind it.
More than 350 elephants have mysteriously died since the start of May, with local sources telling media 70 percent of the deaths occurred around waterholes.
The deaths don't appear to be affecting a particular demographic, with elephants of both sexes and all ages having passed away. The Guardian reports many surviving elephants appear "weak and emaciated, suggesting more will die in the coming weeks".
While it's not clear what's caused the deaths, locals have reported seeing elephants walking in circles and falling to the ground face-first - both signs of mental impairment.
This, alongside a history of cyanide use by opportunistic poachers, has led some experts to speculate the elephants are being poisoned.
However in May, Botswana's government ruled out poaching because none of the elephants's tusks had been removed - the main motive for hunting the animals.
Dr Niall McCann, from charity National Park Rescue, has also ruled out natural anthrax poisoning, which was behind the deaths of more than 100 elephants in the country last year.
Scientists have taken samples from the animals, but are not expecting to get test results back for a couple of weeks yet.
He told the BBC local conservationists spotted 169 elephant carcasses in a three-hour flight in May.
"To be able to see and count that many in a three-hour flight was extraordinary," he said. "A month later, further investigations identified many more carcasses, bringing the total to over 350.
"This is totally unprecedented in terms of numbers of elephants dying in a single event unrelated to drought."
Dr McCann says whatever's killing the animals could even be of concern to humans, particularly if it's something in water or soil. He told the BBC it's currently "a conservation disaster", but also has "the potential to be a public health crisis".
