Nearly 400 elephants have been found dead in Botswana in recent weeks but local authorities and wildlife experts are struggling to find an explanation, with disease and poisoning among the possible causes.
The reports of the deaths in the northern Okavango Delta region first began in early May. Since then, the government has confirmed 275 deaths.
But aerial surveys by wildlife group Elephants Without Borders have counted some 356 elephant carcasses.
Poaching has been ruled out as a cause, as the ivory has not been removed from the elephants.
Infectious disease as well as poisoning by farmers have also been considered and samples from the elephants have been sent to labs in South Africa, Zimbabwe and Canada for testing.