Back in May, Botswana's government ruled out poaching as a reason - noting the tusks had not been removed, according to Phys.org.
There are other things which point to something other than poaching.
"It is only elephants that are dying and nothing else," Dr McCann said. "If it was cyanide used by poachers, you would expect to see other deaths." Dr McCann has also tentatively ruled out natural anthrax poisoning, which killed at least 100 elephants in Botswana last year.
But they have been unable to rule out either poisoning or disease. The way the animals appear to be dying - many dropping on their faces - and sightings of other elephants walking in circles points to something potentially attacking their neurological systems, Dr McCann said.
- TFA